EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, initially ±globular, not motile, branched; showing gravitropism; glycolate oxidase +, glycolate metabolism in leaf peroxisomes [glyoxysomes], acquisition of phenylalanine lysase* [PAL], flavonoid synthesis*, microbial terpene synthase-like genes +, triterpenoids produced by CYP716 enzymes, CYP73 and phenylpropanoid metabolism [development of phenolic network], xyloglucans in primary cell wall, side chains charged; plant poikilohydrous [protoplasm dessication tolerant], ectohydrous [free water outside plant physiologically important]; thalloid, leafy, with single-celled apical meristem, tissues little differentiated, rhizoids +, unicellular; chloroplasts several per cell, pyrenoids 0; centrioles/centrosomes in vegetative cells 0, microtubules with γ-tubulin along their lengths [?here], interphase microtubules form hoop-like system; metaphase spindle anastral, predictive preprophase band + [with microtubules and F-actin; where new cell wall will form], phragmoplast + [cell wall deposition centrifugal, from around the anaphase spindle], plasmodesmata +; antheridia and archegonia +, jacketed*, surficial; blepharoplast +, centrioles develop de novo, bicentriole pair coaxial, separate at midpoint, centrioles rotate, associated with basal bodies of cilia, multilayered structure + [4 layers: L1, L4, tubules; L2, L3, short vertical lamellae] (0), spline + [tubules from L1 encircling spermatid], basal body 200-250 nm long, associated with amorphous electron-dense material, microtubules in basal end lacking symmetry, stellate array of filaments in transition zone extended, axonemal cap 0 [microtubules disorganized at apex of cilium]; male gametes [spermatozoids] with a left-handed coil, cilia 2, lateral, asymmetrical; oogamy; sporophyte +*, multicellular, growth 3-dimensional*, cuticle +*, plane of first cell division transverse [with respect to long axis of archegonium/embryo sac], sporangium and upper part of seta developing from epibasal cell [towards the archegonial neck, exoscopic], with at least transient apical cell [?level], initially surrounded by and dependent on gametophyte, placental transfer cells +, in both sporophyte and gametophyte, wall ingrowths develop early; suspensor/foot +, cells at foot tip somewhat haustorial; sporangium +, single, terminal, dehiscence longitudinal; meiosis sporic, monoplastidic, MTOC [= MicroTubule Organizing Centre] associated with plastid, sporocytes 4-lobed, cytokinesis simultaneous, preceding nuclear division, quadripolar microtubule system +; wall development both centripetal and centrifugal, 1000 spores/sporangium, sporopollenin in the spore wall* laid down in association with trilamellar layers [white-line centred lamellae; tripartite lamellae]; plastid transmission maternal; nuclear genome [1C] <1.4 pg, main telomere sequence motif TTTAGGG, KNOX1 and KNOX2 [duplication] and LEAFY genes present, ethylene involved in cell elongation; chloroplast genome with close association between trnLUAA and trnFGAA genes [precursors for starch synthesis], tufA, minD, minE genes moved to nucleus; mitochondrial trnS(gcu) and trnN(guu) genes +.
Many of the bolded characters in the characterization above are apomorphies of more or less inclusive clades of streptophytes along the lineage leading to the embryophytes, not apomorphies of crown-group embryophytes per se.
All groups below are crown groups, nearly all are extant. Characters mentioned are those of the immediate common ancestor of the group,  contains explanatory material, () features common in clade, exact status unclear.
Sporophyte well developed, branched, branching dichotomous, potentially indeterminate; hydroids +; stomata on stem; sporangia several, terminal; spore walls not multilamellate [?here].
II. TRACHEOPHYTA / VASCULAR PLANTS
Sporophyte long lived, cells polyplastidic, photosynthetic red light response, stomata open in response to blue light; plant homoiohydrous [water content of protoplasm relatively stable]; control of leaf hydration passive; plant endohydrous [physiologically important free water inside plant]; PIN[auxin efflux facilitators]-mediated polar auxin transport; (condensed or nonhydrolyzable tannins/proanthocyanidins +); borate cross-linked rhamnogalactan II, xyloglucans with side chains uncharged [?level], in secondary walls of vascular and mechanical tissue; lignins +; roots +, often ≤1 mm across, root hairs and root cap +; stem apex multicellular [several apical initials, no tunica], with cytohistochemical zonation, plasmodesmata formation based on cell lineage; vascular development acropetal, tracheids +, in both protoxylem and metaxylem, G- and S-types; sieve cells + [nucleus degenerating]; endodermis +; stomata numerous, involved in gas exchange; leaves +, vascularized, spirally arranged, blades with mean venation density ca 1.8 mm/mm2 [to 5 mm/mm2], all epidermal cells with chloroplasts; sporangia in strobili, sporangia adaxial, columella 0; tapetum glandular; sporophyte-gametophyte junction lacking dead gametophytic cells, mucilage, ?position of transfer cells; MTOCs not associated with plastids, basal body 350-550 nm long, stellate array in transition region initially joining microtubule triplets; archegonia embedded/sunken [only neck protruding]; embryo suspensor +, shoot apex developing away from micropyle/archegonial neck [from hypobasal cell, endoscopic], root lateral with respect to the longitudinal axis of the embryo [plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Sporophyte growth ± monopodial, branching spiral; roots endomycorrhizal [with Glomeromycota], lateral roots +, endogenous; G-type tracheids +, with scalariform-bordered pits; leaves with apical/marginal growth, venation development basipetal, growth determinate; sporangium dehiscence by a single longitudinal slit; cells polyplastidic, MTOCs diffuse, perinuclear, migratory; blepharoplasts +, paired, with electron-dense material, centrioles on periphery, male gametes multiciliate; nuclear genome [1C] 7.6-10 pg [mode]; chloroplast long single copy ca 30kb inversion [from psbM to ycf2]; mitochondrion with loss of 4 genes, absence of numerous group II introns; LITTLE ZIPPER proteins.
Sporophyte woody; stem branching axillary, buds exogenous; lateral root origin from the pericycle; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
SEED PLANTS† / SPERMATOPHYTA†
Growth of plant bipolar [plumule/stem and radicle/root independent, roots positively geotropic]; plants heterosporous; megasporangium surrounded by cupule [i.e. = unitegmic ovule, cupule = integument]; pollen lands on ovule; megaspore germination endosporic, female gametophyte initially retained on the plant, free-nuclear/syncytial to start with, walls then coming to surround the individual nuclei, process proceeding centripetally.
EXTANT SEED PLANTS
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); microbial terpene synthase-like genes 0; primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignin chains started by monolignol dimerization [resinols common], particularly with guaiacyl and p-hydroxyphenyl [G + H] units [sinapyl units uncommon, no Maüle reaction]; roots often ≥1 mm across, stele diarch to pentarch, xylem and phloem originating on alternating radii, cork cambium deep seated, gravitropism response fast; stem apical meristem complex [with quiescent centre, etc.], plasmodesma density in SAM 1.6-6.2[mean]/μm2 [interface-specific plasmodesmatal network]; eustele +, protoxylem endarch, endodermis 0; wood homoxylous, tracheids and rays alone, tracheid/tracheid pits circular, bordered; mature sieve tube/cell lacking functioning nucleus, sieve tube plastids with starch grains; phloem fibres +; cork cambium superficial; leaf nodes 1:1, a single trace leaving the vascular sympodium; leaf vascular bundles amphicribral; guard cells the only epidermal cells with chloroplasts, stomatal pore with active opening in response to leaf hydration, control by abscisic acid, metabolic regulation of water use efficiency, etc.; branching by axillary buds, exogenous; prophylls two, lateral; leaves with petiole and lamina, development basipetal, lamina simple; sporangia borne on sporophylls; spores not dormant; microsporophylls aggregated in indeterminate cones/strobili; grains monosulcate, aperture in ana- position [distal], primexine + [involved in exine pattern formation with deposition of sporopollenin from tapetum there], exine and intine homogeneous, exine alveolar/honeycomb; ovules with parietal tissue [= crassinucellate], megaspore tetrad linear, functional megaspore single, chalazal, sporopollenin 0; gametophyte ± wholly dependent on sporophyte, development initially endosporic [apical cell 0, rhizoids 0, etc.]; male gametophyte with tube developing from distal end of grain, male gametes two, developing after pollination, with cell walls; embryo cellular ab initio, suspensor short-minute, embryonic axis straight [shoot and root at opposite ends], primary root/radicle produces taproot [= allorhizic], cotyledons 2; embryo ± dormant; chloroplast ycf2 gene in inverted repeat, trans splicing of five mitochondrial group II introns, rpl6 gene absent; ??whole nuclear genome duplication [ζ/zeta duplication event], 2C genome size (0.71-)1.99(-5.49) pg, two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], 5.8S and 5S rDNA in separate clusters.
IID. ANGIOSPERMAE / MAGNOLIOPHYTA
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, apigenin and/or luteolin scattered, [cyanogenesis in ANA grade?], lignin also with syringyl units common [G + S lignin, positive Maüle reaction - syringyl:guaiacyl ratio more than 2-2.5:1], hemicelluloses as xyloglucans; root cap meristem closed (open); pith relatively inconspicuous, lateral roots initiated immediately to the side of [when diarch] or opposite xylem poles; epidermis probably originating from inner layer of root cap, trichoblasts [differentiated root hair-forming cells] 0, hypodermis suberised and with Casparian strip [= exodermis]; shoot apex with tunica-corpus construction, tunica 2-layered; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, multiseriate rays +, wood parenchyma +; sieve tubes enucleate, sieve plates with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, not occluding pores of plate, companion cell and sieve tube from same mother cell; ?phloem loading/sugar transport; nodes 1:?; dark reversal Pfr → Pr; protoplasm dessication tolerant [plant poikilohydric]; stomata randomly oriented, brachyparacytic [ends of subsidiary cells ± level with ends of guard cells], outer stomatal ledges producing vestibule, reduction in stomatal conductance with increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, overall growth ± diffuse, secondary veins pinnate, fine venation hierarchical-reticulate, (1.7-)4.1(-5.7) mm/mm2, vein endings free; flowers perfect, pedicellate, ± haplomorphic, protogynous; parts free, numbers variable, development centripetal; P = T, petal-like, each with a single trace, outer members not sharply differentiated from the others, not enclosing the floral bud; A many, filament not sharply distinguished from anther, stout, broad, with a single trace, anther introrse, tetrasporangiate, sporangia in two groups of two [dithecal], each theca dehiscing longitudinally by a common slit, ± embedded in the filament, walls with at least outer secondary parietal cells dividing, endothecium +, cells elongated at right angles to long axis of anther; tapetal cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine restricted to the apertural regions, thin, compact, intine in apertural areas thick, orbicules +, pollenkitt +; nectary 0; carpels present, superior, free, several, spiral, ascidiate [postgenital occlusion by secretion], stylulus at most short [shorter than ovary], hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry; suprastylar extragynoecial compitum +; ovules few [?1]/carpel, marginal, anatropous, bitegmic, micropyle endostomal, outer integument 2-3 cells across, often largely subdermal in origin, inner integument 2-3 cells across, often dermal in origin, parietal tissue 1-3 cells across, nucellar cap?; megasporocyte single, hypodermal, functional megaspore lacking cuticle; female gametophyte lacking chlorophyll, four-celled [one module, egg and polar nuclei sisters]; ovule not increasing in size between pollination and fertilization; pollen grains bicellular at dispersal, germinating in less than 3 hours, siphonogamy, pollen tube unbranched, growing towards the ovule, between cells, growth rate (ca 10-)80-20,000 µm h-1, tube apex of pectins, wall with callose, lumen with callose plugs, penetration of ovules via micropyle [porogamous], whole process takes ca 18 hours, distance to first ovule 1.1-2.1 mm; male gametophytes tricellular, gametes 2, lacking cell walls, ciliae 0, double fertilization +, ovules aborting unless fertilized; fruit indehiscent, P deciduous; mature seed much larger than fertilized ovule, small [<5 mm long], dry [no sarcotesta], exotestal; endosperm +, ?diploid [one polar nucleus + male gamete], cellular, development heteropolar [first division oblique, micropylar end initially with a single large cell, divisions uniseriate, chalazal cell smaller, divisions in several planes], copious, oily and/or proteinaceous, embryo short [<¼ length of seed]; plastid and mitochondrial transmission maternal; Arabidopsis-type telomeres [(TTTAGGG)n]; nuclear genome [2C] (0.57-)1.45(-3.71) [1 pg = 109 base pairs], ??whole nuclear genome duplication [ε/epsilon event]; ndhB gene 21 codons enlarged at the 5' end, single copy of LEAFY and RPB2 gene, knox genes extensively duplicated [A1-A4], AP1/FUL gene, palaeo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and three copies of the PHY gene, [PHYB [PHYA + PHYC]]; chloroplast chlB, -L, -N, trnP-GGG genes 0.
[NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]]: wood fibres +; axial parenchyma diffuse or diffuse-in-aggregates; pollen monosulcate [anasulcate], tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.
[AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: phloem loading passive, via symplast, plasmodesmata numerous; vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood + [reaction wood: with gelatinous fibres, G-fibres, on adaxial side of branch/stem junction]; anther wall with outer secondary parietal cell layer dividing; tectum reticulate; nucellar cap + [character lost where in eudicots?]; 12BP [4 amino acids] deletion in P1 gene.
[[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]] / MESANGIOSPERMAE: benzylisoquinoline alkaloids +; sesquiterpene synthase subfamily a [TPS-a] [?level], polyacetate derived anthraquinones + [?level]; outer epidermal walls of root elongation zone with cellulose fibrils oriented transverse to root axis; P more or less whorled, 3-merous [?here]; pollen tube growth intra-gynoecial; extragynoecial compitum 0; carpels plicate [?here]; embryo sac monosporic [spore chalazal], 8-celled, bipolar [Polygonum type], antipodal cells persisting; endosperm triploid.
[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (veins in lamina often 7-17 mm/mm2 or more [mean for eudicots 8.0]); (stamens opposite [two whorls of] P); (pollen tube growth fast).
[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0 [or next node up]; fruit dry [very labile].
EUDICOTS: (Myricetin +), asarone 0 [unknown in some groups, + in some asterids]; root epidermis derived from root cap [?Buxaceae, etc.]; (vessel elements with simple perforation plates in primary xylem); nodes 3:3; stomata anomocytic; flowers (dimerous), cyclic; protandry common; K/outer P members with three traces, ("C" +, with a single trace); A ?, filaments fairly slender, anthers basifixed; microsporogenesis simultaneous, pollen tricolpate, apertures in pairs at six points of the young tetrad [Fischer's rule], cleavage centripetal, wall with endexine; G with complete postgenital fusion, stylulus/style solid [?here], short [<2 x length of ovary]; seed coat?; palaeotetraploidy event.
[PROTEALES [TROCHODENDRALES [BUXALES + CORE EUDICOTS]]]: (axial/receptacular nectary +).
[TROCHODENDRALES [BUXALES + CORE EUDICOTS]]: benzylisoquinoline alkaloids 0; euAP3 + TM6 genes [duplication of paleoAP3 gene: B class], mitochondrial rps2 gene lost.
[BUXALES + CORE EUDICOTS]: mitochondrial rps11 gene lost.
CORE EUDICOTS / GUNNERIDAE: (ellagic and gallic acids +); leaf margins serrate; compitum + [one position]; micropyle?; γ genome duplication [allopolyploidy, 4x x 2x], x = 3 x 7 = 21, 2C genome size (0.79-)1.05(-1.41) pg, PI-dB motif +; small deletion in the 18S ribosomal DNA common.
[ROSIDS ET AL. + ASTERIDS ET AL.] / PENTAPETALAE: root apical meristem closed; (cyanogenesis also via [iso]leucine, valine and phenylalanine pathways); flowers rather stereotyped: 5-merous, parts whorled; P = K + C, K enclosing the flower in bud, with three or more traces, C with single trace; A = 2x K/C, in two whorls, internal/adaxial to C, alternating, (numerous, but then usually fasciculate and/or centrifugal); pollen tricolporate; G [(3, 4) 5], whorled, placentation axile, style +, stigma not decurrent, compitum + [another position]; endosperm nuclear/coenocytic; fruit dry, dehiscent, loculicidal [when a capsule]; floral nectaries with CRABSCLAW expression.
[DILLENIALES [SAXIFRAGALES + ROSIDS]]: stipules + [usually apparently inserted on the stem].
[SAXIFRAGALES + ROSIDS] / ROSANAE Takhtajan / SUPERROSIDAE: ??
ROSIDS / ROSIDAE: anthers ± dorsifixed, transition to filament narrow, connective thin.
[ROSID I + ROSID II]: (mucilage cells with thickened inner periclinal walls and distinct cytoplasm); if nectary +, usu. receptacular; embryo long; chloroplast infA gene defunct, mitochondrial coxII.i3 intron 0.
ROSID I / FABIDAE / [ZYGOPHYLLALES [the COM clade + the N-fixing clade]]: endosperm scanty.
[the COM clade + the N-fixing clade]: ?
[FABALES [ROSALES [CUCURBITALES + FAGALES]]] / the N-fixing clade / fabids: (N-fixing by associated root-dwelling bacteria); tension wood +; seed exotestal.
[ROSALES [CUCURBITALES + FAGALES]]: (actinomycete Frankia infection +); styles separate; ovules 1-2/carpel, apical.
[CUCURBITALES + FAGALES]: P parts similar; ovary inferior; fruit 1-seeded, indehiscent.
FAGALES Engler - Main Tree.
Plant ectomycorrhizal; (flavonols), dihydroflavonols, ellagic acid +; vessel elements also with scalariform perforation plates, aggregate rays +; sieve tubes with non-dispersive P-protein bodies; (cork cambium outer cortical); buds perulate; lamina margins toothed, secondary veins proceeding straight to teeth [venation craspedodromous], teeth not glandular, with higher-order veins convergent on them [= urticoid]; plants monoecious, inflorescence with compact cymose clusters of flowers, flowers very small, (± monosymmetric by reduction), sessile; P +, uniseriate; nectary 0; staminate flowers: inflorescence a catkin; A arrangement?; pollen oblate, thickened sexine arches going from pore to pore, visible as bands [arci], cavity between inner and outer pores [vestibulum], tectum ± spinulate, infratectum granular; carpelate flowers: style undivided, ± 0, stigma ± decurrent, linear, dry; ovule 2/carpel, pendulous, epitropous, unitegmic, suprachalazal tissue massive; megaspore mother cells several; ovules poorly developed at pollination, fertilization delayed; fruit ± a nut; testa vascularized, not mechanical, exotesta often enlarged and persisting; cotyledons large. - 7 families, 33 genera, 1,175 species.
Note: In all node characterizations, boldface denotes a possible apomorphy, (....) denotes a feature the exact status of which in the clade is uncertain, [....] includes explanatory material; other text lists features found pretty much throughout the clade. Note that the precise node to which many characters, particularly the more cryptic ones, should be assigned is unclear. This is partly because homoplasy is very common, in addition, basic information for all too many characters is very incomplete, frequently coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there are the not-so-trivial issues of how character states are delimited and ancestral states are reconstructed (see above).
Age. Ages for crown-group Fagales suggested by Cook and Crisp (2005) are 95-75 Ma and by X.-G. Xiang et al. (2014) rather older, (107.3-)105.2(-101.3) Ma, while Sauquet et al. (2011) give a range of dates from (124.8-)120.2-67.3(-48.9) Ma and Xing et al. (2014) suggest ages of 125-91.8 m. years; at around 92 Ma the dates in Larson-Johnson (2015) fit with most of these. Ages of (106.5-)104.9, 104.1(-99.9) Ma in H.-L. Li et al. (2015) show little spread, while the youngest dates, at around 68.6-62.2 Ma, are those of Xue et al. (2012), and of ca 61 Ma, that of Quirk et al. (2012). Other dates: ca 82.3 Ma (Tank et al. 2015: Table S2). See also dates in Tedersoo and Brundrett (2017).
For fossils in the Nothofagus area, so crown Fagales, that are up to ca 84 Ma, see Dettmann et al. (1990) and Dettmann (1994).
Evolution: Divergence & Distribution. From the rich fossil record of Fagales, Friis et al. (2006a) suggested that all major fagalean lineages were present at the latest by the Cenomanian (early Late Cretaceous), ca 97 Ma, and fagalean leaf fossils of this age are reported from Queensland, Australia - at that time, Australia had barely separated from Antarctica (e.g. McLoughlin et al. 1995). For Normapolles pollen, see below.
X.-G. Xiang et al. (2014) discuss diversification of the order in considerable detail, emphasising the distinction between wind- (most species of Fagus were included here!) and animal-dispersed fruits, and also the closed habitats preferred by species in the former group and the open habitats preferred by species in the latter group; they also detected a number of shifts in diversification rates. Larson-Johnson (2015) integrated fossils with fruits in a study of fruit evolution and diversification patterns in the order, suggesting that clades with biotically dispersed propagules had both larger ranges and often higher diversification rates than did clades with abiotically dispersed propaguless, in the former, scatter-hoarding by jays and small rodents was most commonly involved. Wind dispersal is perhaps the plesiomorphic condition in Fagales (Larson-Johnson 2015: ?outgroups), while within the order there have been around seven transitions to biotic dispersal and four to abiotic dispersal, three of the latter being reversals.
The morphologies of flowers of some Cretaceous fossils placed in or near Fagales are substantially different from those of extant members. Thus there are suggestions of nectary lobes between the stamens in the staminate and perfect flowers of Antiquacupula and the inner walls of the fruit loculi are glabrous; the flowers have a floral formula of T 3 + 3; A 12, dorsifixed; nectaries +, G , inferior (Sims et al. 1998; Herendeen et al. 1999). Unnamed fossils from Massachusetts have a character combination of flowers perfect, P 6, A 12, adnate to P, nectaries, inferior ovary with ovules mature at time of pollination, and single-seeded and very small fruits that are just possibly dehiscent (Taylor et al. 2012). If they belong to stem Fagales, single-seeded fruits may have evolved before wind pollination; the very small size of the seeds/fruits (<2 mm long) is consistent with the age of the fossils, ca 75 Ma in the Campanian, since flowers then tended to be small (Taylor et al. 2012). Taylor et al. (2012) suggested that the members of the uniseriate perianth might be connate via hairs, but note that the perianth bases are very small, in this respect being rather unlike sepals in the rosids. For fossils, see especially Friis et al. (2011), while Larson-Johnson (2015) placed a number of fossils with fruits on a phylogenetic tree of the order (see the supplementary material for a critical evaluation of the fossil material, ages of fossils assigned to extant genera, data matrix, etc.). The recently described 94-90 Ma Soepadmoa from New Jersey has some features reminiscent of Nothofagus, as well as unique (for Fagales) characteristics such as tepals that become enlarged and large, strongly-toothed primary bracts. Archaefagacea has a tricarpelate gynoecium, two ovules per carpel and sometimes three-seeded fruits (Takahashi et al. 2008a); Gandolfo et al. (2018) suggest this is unlikely to be crown-group Fagales.
Where change in infratectum structure is to be placed on the tree seems unclear when treated at the family level; either one gain, an ordinal apomorphy, and one reversal (Fagaceae), or two gains (see also Doyle 2009), and there are similar problems when optimising fruit charaters (cupules, with valves). For the evolution of the foot layer, see Denk and Tekleva (2014); the ancestral state for Fagaceae - foot layer thick, regular - should be pegged to this node, but I do not know variation in the foot layer above Fagaceae. However, Jiang et al. (2019) discuss the evolution of pollen morphology for the whole order.
Schönenberger et al. (2001b) and Friis et al. (2003a) give useful tables comparing the morphology of extant and fossil members of Fagales; see also Crepet et al. (2008), Takahashi et al. (2008a) and Taylor et al. (2012: some outgroups). The roots of ECM Fagales tend to be narrow in diameter, but the same is also true of roots of Rosales, so it could be a plesiomorphic feature for Fagales (Valverde-Barrantes et al. 2017).
Ecology & Physiology. Fagales are the largest clade of extant seed-plants in which ectomycorrhizal (ECM) associations are pervasive. Nevertheless, although they are hardly particularly speciose (e.g. Magallón & Sanderson 2001), members, especially Fagaceae, can dominate the forests in which they grow, and this is discussed further under individual families and also in Clade Asymmetries, while plant-fungal associations in general are discussed elsewhere. The order is now particularly well represented in forests in arctic to temperate and in tropical montane regions and the climatic preferences of the immediate ancestor of the order may have been for more or less warm and aseasonal temperate conditions.
ECM Agaricales are common on Fagales, and the crown group origins of the 10 or so clades involved are split almost equally between Late Cretaceous and Eocene (Ryberg & Matheny 2012). However, the relative timing of diversification of the ECM fungi and of Fagales is unclear. In Boletales, at least, ECM fungi may have evolved from brown rot fungi in the ecological context of soils low in nitrogen (N) (and high in organic material) formed by the activities of these fungi. Dates of origin of ECM associations there - which happened more than once - are also late Cretaceous and younger (Eastwood et al. 2011). See also Brundrett (2017a), Tedersoo (2017b) and Tedersoo and Brundrett (2017) for literature, dates, etc.. For additional information, see papers in Martin (2017).
AM associations are not very common in Fagales, but it is interesting that they occur in groups that are known to fix N (Rose 1980). For N fixation by Frankia, the bacterium involved in N fixation in this clade, see also elsewhere.
Pollination Biology & Seed Dispersal. Wind pollination and monoecy pervade the order, although taxa like Lithocarpus are pollinated by insects, and insect pollination may have occurred in some fossil taxa, too. Delayed fertilization, intermittent pollen tube growth (e.g. Sogo & Tobe 2005, 2006a, b, d [the last for a summary]), and chalazogamy (see e.g. Benson 1894; Nawashin 1899; Swamy 1948b and references) are also common, however, chalazogamy is not an apomorphy for the order (fertilization of Nothofagaceae is unknown and Fagaceae, Myricaceae and some Juglandaceae are porogamous). Delayed fertilization, which also occurs in Fagaceae, is associated with the immaturity of the ovules at pollination and competition between the ovules and sometimes between the several embryo sacs that develop within the one ovule (see Sogo & Tobe 2005d). The immaturity of the ovules can be extreme, thus in Corylus avellana the ovules do not even begin to develop until after pollination (Germain 1994).
Fruits throughout the order are single-seeded, as is very common in wind-pollinated plants, whatever the number of ovules in the young ovary - note, however, this feature may be an apomorphy for [Fagales + Cucurbitales]. See Tiffney (1986a) and especially Larson-Johnson (2015) for the evolution of fruits in Fagales, both animal dispersal (especially scatter-hoarding) and various kinds of wind dispersal being involved.
Plant-Animal Interactions. Interestingly, larvae of both Heterobathmiidae (the adults have jaws) and Eriocraniidae (Glossata: most lepidoptera, with a proboscis), the two basal clades in the lepidopteran Angiospermivora, are found as leaf miners on Fagales, on Nothofagaceae and on Fagaceae and Betulaceae (also Rosaceae) respectively (Shields 1988; Imada et al. 2011; Regier et al. 2015). Phyllonorycter leaf-mining moths, members of the fairly basal glossatan microlepidopteran Gracillariidae-Phyllocnistinae, are also quite common here, with about half the known host records being on members of Fagales (Lopez-Vaamonde et al. 2003; see also Regier et al. 2013; Kawahara et al. 2016). Diversification of the moth clade seems to have occurred about 50.8-27.3 Ma, well after that of Fagales (see above), although the origination of the clade was some 76.3-50.3 Ma (Lopez-Vaamonde et al. 2006). Lycaenidae caterpillars are also quite commonly to be found on members of Fagales (see Fiedler 1991).
Bacterial/Fungal Associations. Associations with N-fixing Frankia bacteria are sporadic; for the strains of Frankia associated with N-fixing Fagales, see elsewhere. For stem-group ages of N-fixing clades, Late Cretaceous, see H.-L. Li et al. (2015). See also above under Ecology & Physiology and links there.
Apart from Agaricales, Sebacinales-Sebacinaceae are other ECM fungi commonly associated with Fagales (Weiß et al. 2016). Some ECM fungi form tuberculate structures on the roots of Quercus (Smith & Pfister 2009). For additional information, see papers in Martin (2017).
Rusts on Fagales are predominantly members of Pucciniastraceae, a group also to be found on ferns (Savile 1979).
Genes & Genomes. Plant haplotypes are widely shared between taxa, sometimes apparently quite distant according to relationshps suggested by the nucleome, not only in Fagaceae but also in Nothofagaceae and Juglandaceae (Simeone et al. 2016).
Chemistry, Morphology, etc.. Although the perianth parts in Fagales are small, they may have three traces, and petals/inner tepals with three traces are also found in some fossil taxa. Carpel orientation and integument number are variable. Ovule structure is unclear in part because of the great development of megaspore mother cell tissue in some taxa and the relation of these mother cells to the cells of the mature embryo sac. Taylor et al. (2012) suggested that an ovule that is straight when young, becoming curved only later, might be a distinctive feature of the order. Germination is often both hypogeal and epigeal in the one family.
For chemistry, see Giannasi (1986); for cork cambium initiation, see Weiss (1890); vegetative morphology, see Hickey and Taylor (1991); flower and inflorescence morphology, see Abbe (1974); pollen, see Zavada and Dilcher (1986), Feuer (1991) and especially Friis et al. (2006a); embryology, Benson (1894) and Xing et al. (1998); and for fruit wall anatomy, see Soepadmo (1967b).
Phylogeny. Relationships within Fagales are fairly well resolved, although the position of Myricaceae remains uncertain. Manos and Steele (1997) placed Myrica as sister to [Casuarinaceae [Ticodendraceae + Betulaceae]] in a matK and combined matK + rbcL analysis, although support was weak (see also Sauquet et al. 2012: 67% bootstrap support), but sister to all Fagales except Nothofagaceae and Fagaceae in a rbcL analysis, the latter set of relationships also being found by R.-Q. Li et al. (2002: only 61% bootstrap support) using trnL-F sequence data. Cook and Crisp (2005) found the relationships [Juglandaceae [Myricaceae [Casuarinaceae + Betulaceae]]]. R.-Q. Li et al. (2004: six genes, all three genomes) found Myricaceae to be sister to Juglandaceae, although still support was not strong, as did Herbert et al. (2006: three genes, little support for the position of Myricaceae); support was, however, good in the Bayesian analysis of Soltis et al. (2007a: sampling poor; see also Larson-Johnson 2015: support not strong; H.-L. Li et al. 2016). A recent comprehensive five-locus chloroplast phylogeny of Fagales has not changed the situation, and although there was some support for a [Juglandaceae [Myricaceae + The Rest]] clade, it was not strong (X.-G. Xiang et al. 2014) and that topology was also recovered by Xing et al. (2014), H.-L. Li et al. (2015) and M. Sun et al. (2016) and Z.-D. Chen et al. (2016), the last two including details of infrafamilial relationships.
Previous Relationships. Fagales are the core of the old "Englerian" Amentiferae which have since been comprehensively demolished; within a somewhat larger group, Juliflorae, were to be found all broad-leaved angiosperms with very reduced flowers, so including Platanaceae, Lacistemaceae, Chloranthaceae, Piperaceae, etc. (e.g. Eichler 1878). Its members have since found resting places among many otherwise entirely unrelated groups within eudicots such as Malpighiales (Salicaceae), Proteales (Platanaceae), and Rosales (Ulmaceae and relatives: e.g. Qiu et al. 1998), and in or near the magnoliids (Piperaceae, Chloranthaceae respectively). They also included Eupteleaceae (Ranunculales), Myrothamnaceae (core eudicot), and Eucommiaceae (Garryales, a lamiid). In the late nineteenth and early twentieth centuries in particular, a number of botanists thought that Amentiferae were primitive, and the chalazogamy common in the order was thought to be intermediate between fertilization in some gymosperms and the porogamy of most angiosperms (e.g. Nawaschin 1895). Hamamelid taxa such as Altingiaceae and Hamamelidaceae seemed to be intermediate between Amentiferae and more conventional broad-leaved angiosperms, but they, too, are not related to Fagales (see Saxifragales here).
Fagales comprise the Faganae and two and a half more superorders in Takhtajan (1997).
Includes Betulaceae, Casuarinaceae, Fagaceae, Juglandaceae, Myricaceae, Nothofagaceae, Ticodendraceae.
Synonymy: Juglandineae Thorne & Reveal, Myricineae Thorne & Reveal - Betulales Martius, Carpinales Döll, Casuarinales Berchtold & J. Presl, Corylales Dumortier, Juglandales Berchtold & J. Presl, Myricales Martius, Nothofagales Doweld, Quercales Burnett, Rhoipteleales Reveal - Casuarinanae Reveal & Doweld, Faganae Takhtajan, Juglandanae Reveal
NOTHOFAGACEAE Kuprianova - Back to Fagales
(Plant deciduous); chemistry?; sclereid nests?; peltate glandular hairs +; perulae decussate; leaves two-ranked (spiral), lamina (punctate), vernation various, (margins entire), stipules usu. peltate, enclosing colleters; staminate flowers: P connate; A 10-15(-many), basifixed, connective usu. produced; pollen 3-10 colpate, colpi short, margins raised, surface short-spiny, tectate-granular; pistillode 0; carpelate flowers: 1-3 together; P -≤4 small scales; (staminodes +); G [2-3], median member abaxial, stigma-style ± strap-shaped; ovule integument 4-7 cells across, parietal tissue 1-2 cells across, nucellar cap 0, supra-chalazal tissue massive, postament +, flat-topped; megaspore mother cells?; fertilization?; cupule +, single, 2-(3-)4-valved, lamellate; nuts (1-)3(-7)/cupule, angled [lenticular (central - 2-carpelate)/triangular (lateral - 3-carpelate)], wall with transversely elongated sclereids in middle; testa?; endosperm 0, suspensor ?0, cotyledons folded; n = 13; ?germination.
1 [list]/35. New Guinea to South America (map: from Good 1974, slightly modified; green, Cretaceous to Mid-Caenozoic fossils [also in Australia, New Zealand and South America where the genus is currently found], from Dettmann et al. 1990). [Photo - Branch.]
Age. Cook and Crisp (2005) estimated the age of crown group Nothofagaceae at only (66-)58-ca. 43(-ca 35[?-21]) Ma, i.e., decidedly after the first fossil records (see below), while Heads (2006), accepting the identity of those fossils, saw a crown-group age of around 72 Ma at least. Sauquet et al. (2012) used a variety of calibrations and obtained ages ranged from (113.6-)100.3-23.5(-13.3) Ma, while (77-)76.7(-75.2) Ma is the estimate in X.-G. Xiang et al. (2014). A crown age of ca 36 Ma was suggested by Quirk et al. (2012), while ca 65 Ma is the crown-group age in Premoli et al. (2011).
Fossils identified as belonging to all four subgenera are known from the Late Campanian 73-71 Ma in Antarctica (Dettmann et al. 1990; Swenson et al. 2001; Cantrill & Poole 2005) and Nothofagus-like pollen (Nothofagites) characterized southern temperate Gondwanan areas during the later Cretaceous (Nichols & Johnson 2008). Given such dates and non-fossil estimates of ages of groups within Nothofagus, the pollen types must have evolved in parallel (Cook & Crisp 2005), or the pollen has been misinterpreted, or some of the age estimates are (very) incorrect.
Evolution: Divergence & Distribution. Bouchenak-Khelladi et al. (2015) suggested that there was a slow-down in diversification rate here.
The biogeography of Nothofagus has been much discussed. The general pattern of diversification in the genus is the "broom and handle" type (Cook & Crisp 2005); either persistence of a not very speciose lineage, or diversification followed by near-extinction and then diversification again. Fossil evidence points strongly towards a southern distribution in the Cretaceous. Is the current distribution of the genus a reflection of continental drift, with the massings of species seen today relecting ancestral massings (Heads 2006)? Here global vicariance is involved, Nothofagaceae being the southern representatives of Fagales that initially were distributed more or less world-wide, especially in extra-tropical areas. Or perhaps dispersal has shaped the distribution of the family (e.g. Swenson et al. 2001; in particular Sauquet et al. 2011)? Thus Knapp et al. (2005) and Cook and Crisp (2005) suggested that Nothofagus reached New Zealand, at least, by long distance dispersal only ca 30 Ma, and Brassospora-type plants have since become extinct there (see also Pole 2003; Waters & Craw 2006; Wallis & Trewick 2009); McCulloch and Waters (2019) discuss how to interpret the ages of fossils found in places like New Zealand with controversial geological histories. Kooyman et al. (2014) noted that the Neogene recolonization of New Zealand resulted in rainforests different from those in Australia, etc., while Y. Sun et al. (2014) argued strongly for the continued presence of an emergent New Zealand landmass, their focus group being the liverwort Schistochilaceae, common in Nothofagus forests, de Queiroz (2014 and references) thought that New Zealand had been submerged perhaps 25-23 Ma, while Wallis and Jorge (2018; see also He et al. 2016) argue strongly for the persistence of an emergent New Zealand (see also Oliveros et al. 2019 and references: birds)... As to Nothofagus on New Caledonia, there are similar arguments (Nattier et al. 2017 and references; Giribet & Baker 2019). Further complicating the issue, there are also questionable reports of Caenozoic Nothofagus pollen from the Gulf Coast of the USA as well as in the Pacific North West (Elsik 1974).
The late Cenomanian/Early Turonian (ca 93.5 Ma) southermost pollen province is characterized by Nothofagites pollen (e.g. Kedves 1989; Friis et al. 2011). Although Podocarpaceae were common in Eocene Patagonia, at the end-Eocene - early Oligocene, Nothofagus came to dominate in these southernmost areas (Pujana & Ruiz 2017). Nothofagoxylon is the predominant angiosperm wood in Antarctica by the mid-Campanian ca 78 Ma, and in the Palaeocene and Eocene it further increased in proportional abundance, although conifers may have been replacing non-Nothofagus angiosperms and Nothofagus may not have been very common in Patagonia then (Cantrill & Poole 2005). As Cantrill and Poole (2005, see also 2012) emphasized, different groups of Nothofagus were involved over time - first section Nothofagus predominated, then sect. Lophozonia, while sect. Fuscospora also became quite common in the Eocene and later (see also Kooyman et al. 2014). The ancestral niche for the genus may be mesothermal - or rather cooler, depending on how niches are reconstructed (Hinojosa et al. 2016). Even as the climate in Antarctica deteriorated, N. fusca-type plants in particular persisted until the Pliocene ca 3 Ma if only in tundra-type vegetation, although exactly when woody vegetation finally became extinct is unclear (Cantrill & Poole 2012 for detailed discussion).
Three of the four pollen types in the genus occur in the same locality in the Oligocene in Tasmania and the fourth was found nearby (Hill 2001 and references). Since the distribution of Nothofagus currently spans latitudes from almost 0-50+o S, and individual groups have latitudinal preferences, either the climatic preferences of the clades have changed, or there was a very distinctive climate in Tasmania in the Oligocene, or... (Hill & Brodribb 2006). Perhaps this is a late example of the general intermingling of taxa with now very different climatic preferences similar to that which occurred earlier in the equable early Caenozoic (Palaeocene-Eocene) climates. Similarly, Nothofagus in Miocene Patagonian South America was represented by three pollen types (Palazzesi & Barreda 2007), and all four subgenera are known from Antarctica in the later Cretaceous (see above).
For characters and clades in Nothofagus s.l., see Heenan and Smissen (2013). Fernández et al. (2016) discuss the ancestral pollen morphology of Nothofagus.
Ecology & Physiology. Nothofagaceae have played a major role in more temperate southern hemisphere forests from the later Cretaceous onwards. Extant Nothofagus forms forests with bamboo, the latter making up the understory, in both South America and Papua (Kappelle 2006b: see also Fagaceae).
In Chile, ignoring the emergent Nothofagus dombeyi, the other trees in forests both with and without the plant had similar carbon sequestration levels, that of N. dombeyi, when present, essentially being an add-on and almost doubling the total (Parada et al. 2018); see also Dipterocarpaceae.
Pollination Biology & Seed Dispersal. Poole (1952) did not observe actual fertilization, but noted thst 9-10 weeks elapsed between pollination and fertilization.
Plant-Animal Interactions. The ten species of the jawed moth Heterobathmia (Heterobathmiidae), a jawed moth, make their homes exclusively on Nothofagus, both as an adult - they eat pollen - and as a caterpillar - they are leaf miners (see also Futuyma & Mitter 1996). Heterobathmiidae are perhaps sister to Agathiphagidae (food plant Agathis), the two diverging perhaps ca 158.5 Ma (Wahlberg et al. 2013; see also Heikkilä et al. 2015), although the latter are more probably one clade down the lepidopteran tree and sister to Micropterigidae (Regier et al. 2015; Kristiansen et al. 2015). Ages of around 125 Ma have also been suggested, and Mitter et al. (2016) suggest that Heterobathmia is sister to all other Angiospermivora, being three branches up the lepidopteran tree.
Bacterial/Fungal Associations. Humphries et al. (1986: c.f. more recent ideas of relationships) discuss the parasites and associates of Nothofagus, and suggest the possibility of some co-evolution of the genus with Eriococcus scale insects that grow on it. The inaperturate discomycete Cyttaria grows on Nothofagus in both the Antipodes and South America, but neither in New Guinea nor in New Caledonia. Only subgenera Fuscospora and Lophozonia are affected, and the pattern of association of host and parasite is not simple; the split between Australian and New Zealand species of Cyttaria is estimated at ca 44.6-28.5 Ma (K. Peterson et al. 2010), overlapping with Crisp and Cook's estimates above.
Tedersoo et al. (2008) examined ECM fungi on Tasmanian Nothofagus), and other than basidiomycetes, Tuberaceae and associated clades (ascomycetes) are also found on the genus (Bonito et al. 2013). ECM fungi found on Nothofagaceae and Myrtaceae, both southern groups, are similar, perhaps because the fungi moved from the former onto the latter as the climate became drier (Tedersoo et al. 2008, 2014a).
The rust parasites of Nothofagaceae are rather different from those of other Fagales (Savile 1979).
Chemistry, Morphology, etc.. Nothofagus obliqua may have unilacunar nodes; does it have stipules?
Unlike Fagaceae, there is no obvious relationship between the number of fruits and the number of valves of the cupule. The central flower of the cupule often has two carpels, lateral flowers have three. Staminate flowers that apparently have many stamens are interpreted as being the result of the fusion of separate flowers of a dichasium (see also Betulaceae). Embryology is poorly known; Poole (1952) suggested that it is the chalazal megaspore that develops, and the cotyledons are at the micropylar end of the seed and the radicle at the antipodal end...
Further information (sometimes under Fagaceae) may be found in Hill and Jordan (1993) and Kubitzki (1993b), both general, Hegnauer (1989: chemistry), Lersten and Horner (2008b: leaf crystals, etc., Fagaceae are similar), Philipson and Philipson (1979: leaf vernation), Langdon (1947) and Poole (1950), inflorescence and cupule, Rozefelds (1998) and Rozefelds and Drinnan (1998), stamens and staminate flowers, and Praglowski (1982) Crepet and Daghlian (1980) and Fernández et al. (2016), pollen. There is also a website, Nothofagus, les hêtres du bout du monde..., nothofagus.free.fr, that will be of interest to francophone visitors.
Phylogeny. Manos (1997), Knapp et al. (2005 and references) and Heenan and Smissen (2013) discuss relationships within the genus, which are [Lophozonia [Fuscospora [Brassospora + Nothofagus]]]; see also X.-G. Xiang et al. (2014). For relationships suggested by plastomes, rather different, see Premoli et al. (2012); there is a strong geographical signal.
Classification. For sections, see Philipson and Philipson (1988), for a checklist and bibliography, see Govaerts and Frodin (1998: in Fagaceae), and for generic limits, see Heenan and Smissen (2013) and Hill et al. (2015).
Previous Pelationships. Nothofagus has often been included in Fagaceae, as by Cronquist (1981) and Kubitzki (1993b).
[Fagaceae [[Myricaceae + Juglandaceae] [Casuarinaceae [Ticodendraceae + Betulaceae]]]: bud scales spiral; leaves spiral; anthers dorsifixed; endocarp parenchymatous.
Age. Estimates of the age of this node are (65-)61(-57) Ma (Wikström et al. (2001), 62.7 Ma (Tank et al. 2015: Table S1, S2), and (93-)90, 88(-84) Ma old (H. Wang et al. 2009: Bayesian relaxed clock estimates up to 100 My). Magallón and Castillo (2009) estimated an age of ca 93.5 Ma, Bell et al. (2010) ages of (68-)55, 55(-40) Ma, and X.-G. Xiang et al. (2014) an age of (101.2-)99.3(-95.5) Ma. Naumann et al. (2013) offered an age of ca 52.8 Ma but the age of around 110.3 Ma in Sauquet et al. (2011) is almost double this, while (99.3-)97.3(-87.3) Ma is the age in X.-Y. Yang et al. (2018).
Evolution: Plant-Animal Interactions. Some larvae of Eriocranidae, a small group of near-basal lepidoptera, are found as leaf miners on this clade (Powell et al. 1998).
Chemistry, Morphology, etc.. For the parenchymatous endocarp, see Manchester (2011), ?Nothofagaceae.
FAGACEAE Dumortier, nom. cons. - Back to Fagales
Hairs often stellate/branched; sclereid nests in bark, cells with large rhomboidal crystals; veins often associated with crystals only; lamina vernation conduplicate-plicate; inflorescence branched or not; flowers often trimerous; P biseriate [thus = T] or not, 4-6(-9), (connate); staminate flowers: bract; A (4-)12(-20) (connective produced); pollen tectate-columellate, not spiny; pistillode +; carpelate flowers: G , alternating with P, or median member abaxial; ovules bitegmic (unitegmic), funicle evident, central strand in supra-chalazal tissue; embryo sac with chalazal caecum; cupule +, with valves [one more than fruit number], ± spiny; nut trigonous, wall with lignified tissue to the outside, endocarp hairy inside; seeds pachychalazal; (endosperm cellular), 0; germination epigeal; n = 12 (13, 21).
7 [list]/730 (927)- 2 subfamilies below. More or less worldwide (map: from Soepadmo 1972; Fl. N. Am. III. 1997; M. V. Catro Campos in Nixon 20).
Age. Estimates for the crown age of the family are 37-34 Ma (Wikström et al. 2001), 77-67 Ma (Cook & Crisp 2005), (45-)31, 28(-16) Ma (Bell et al. 2010), or (103.6-)84.7, 82.3(-64.2) Ma (Sauquet et al. 2012); see Grímsson et al. (2016: Table 2) for more suggestions.
The oldest Fagaceae fossils are some 90 Ma old (Crepet et al. 2004 for references), while Grímsson et al. (2016) discuss fossils from Wyoming assignable to stem Quercoideae and Fagoideae, as well as to an extinct clade of Fagaceae, in deposits that are dated to 81-80 Ma.
1. Fagoideae K. Koch
Plant deciduous; ellagic acid 0; stomata also cyclocytic; leaves two-ranked; staminate flowers: male inflorescence capitate; pollen subprolate-spheroidal, tectum with ± flat-lying and fused rod-like elements; pistillode 0; carpelate flowers: staminodes 0; styles long, recurved, stigma capitate; ovule ?straight, micropyle bistomal, elongate, inner integument thinner than outer, parietal tissue 5< layers across, ?nucellar cap ca 13 cells across; pollen tube at ovule at dormancy; nuts 2/cupule; cotyledons folded; genome size [1C] 0.56-0.63 pg; germination epigeal.
1/10. Temperate N. hemisphere. [Photo - Fruiting Branch, © M. Brand.]
Age. Estimates of the crown-group age of Fagoideae are (24-)16.2, 15.7(-8.4) Ma (Xing et al. 2014), (24.2-)17.2(-7.9) Ma (X.-G. Xiang et al. 2014), (62-)53(-43) Ma (Renner et al. 2016) and 51-39 Ma (Grímsson et al. 2016).
2. Quercoideae Örsted
(Plant deciduous); leaves (two ranked/whorled), (margins entire/lobed/biserrate); inflorescence spike or catkin, staminate and carpelate flowers on separate inflorescences or not; staminate flowers: sessile; pollen prolate, exine (micro)verrucate/scabrate, ± striate; pistillode +, (secreting nectar); carpelate flowers: staminodes +; (style relatively long, occupying most of the gynoecium), stigmas capitate/linear-decurrent/punctiform and with a terminal pore; ovule with integuments the same length [micropyle endostomal?], parietal tissue one cell across, nucellar cap ca 2 cells across, (tracheids +); pollen tubes branched, in style at dormancy; cupule also cup-shaped, with scales/lamellae, (largely enclosed by woody receptacle); nuts 1-3(-15< - Trigonobalanus)/cupule, (rounded), (endocarp glabrous inside - some subgenus Quercus); (endosperm with basi-lateral caecum), (cotyledons connate); genome size [1C] 0.5-1.3 pg; rpl22 gene transferred from chloroplast to nucleus; germination often hypogeal.
6/890: Quercus (480), Lithocarpus (250), Castanopsis (150). N. temperate, at higher elevations in the tropics, not S. Africa or New Zealand, barely in Australia. [Photo - Fruit]
Age. Estimates of the crown-group age of Quercoideae are around (58.1-)48.7(-43.8) Ma (Sauquet et al. 2012) or (66.1-)56.4(-50.6) Ma (X.-G. Xiang et al. 2014); see Grímsson et al. (2016) for more suggestions.
Fossils of Castanopsis, ca 52 Ma and to be placed in the crown group of the genus, are known from Argentina (Wilf et al. 2019), and they make the ages above somewhat problematic.
Synonymy: Castaneaceae Brenner, Quercaceae Martinov
Evolution: Divergence & Distribution. For more ages, see Xing et al. (2014), X.-G. Xiang et al. (2014) and Deng et al. (2017: Quercus). The later Cretaceous Protofagacea, with 6 tepals and 12 stamens (Herendeen et al. 1995) and early Eocene Fagus scofieldii (Mindell et al. 2009) have fruits with a hairy endocarp, like most extant Fagaceae. For Cretaceous fossil leaves perhaps to be assigned to Fagaceae, see Gnilovskaja and Golovneva (2016). Grímsson et al. (2016) provide images of pollen and leaves and an evaluation of the fossil record. Indeed, the diversity of the family in the earlier Caenozoic was considerable with numerous records from throughout the northern hemisphere (e.g. Manchester & Crane 1983: fruits very small, ?wind dispersed; Herendeen et al. 1995; Manchester & Dillhoff 2004: Fagus 50 Ma from British Columbia; Mindell et al. 2007; Kvacek 2008; Denk et al. 2012; Bouchal et al. 2014; Grímsson et al. 2015a: Eocene of W. Greenland).
Past distributions may differ from those of today. Thus fossils of Lithocarpus, now basically South East Asian-Malesian, are widespread in the northern hemisphere, and there have also been preliminary reports of fossils of Fagaceae from Early Eocene deposits in Argentinian Patagonia (M.-Q. Liu & Zhou 2006; Hermsen & Gandolfo 2016). These latter have been confirmed: ca 52 Ma fruiting fossils of Castanopsis rothwellii, apparently to be included in the crown group of the genus, have recently been described from Argentina; leaves, probably of this species, were originally described as Tetracera, in Dilleniaceae (Wilf et al. 2019), and this recent description of Castanopsis from Palaeocene deposits in Argentina has occasioned some interest. Furthermore, a number of taxa from these ca 52 Ma deposits in Argentina are now known only from forests in Australasia. Castanopsis may have moved from North to South America, thence to Australia, and finally to (Indo-)Malesia. There it and a number of other genera known fossil from these deposits like Ceratopetalum Papuacedrus, Ripogonum, Agathis, Dacrycarpus, Eucalyptus, Casuarina and Todea, all of which have since become extinct in South America, are now to be found (Wilf et al. 2019: biome conservatism). Genera like Retrophyllum, also found in such deposits (Wilf et al. 2017b), are still to be found in both areas. However, fossils like Castanopsis rothwellii (placed in Castanopsoidea) are known from Palaeocene-Eocene deposits in Tennessee (Crepet & Nixon 1989), and Denk et al. (2019) suggest that the exact phylogenetic position of these fossils is unclear and there is no pollen of "Castaneoideae" in the southern part of the world; to them, this southern route of Castanopsis seemed unlikely. Indeed, fossils of Fagaceae are overwhelmingly from the northern hemisphere, and the likely area of origin of the family is there.
For more information on the evolution and biogeographic relationships of Fagaceae, see e.g. Manos and Stanford (2001) and Manos et al. (2002) and Grímsson et al. (2016) and for those of Fagus in particular see Denk and Grimm (2009a). Larson-Johnson (2015: Fig. 10) discuss increases in diversification rates in the family, while Bouchenak-Khelladi et al. (2015) discuss increases within Quercoideae and possible factors triggering them, including moving into Mediterranean-type climates.
Axelrod (1983; see also Bouchal et al. 2014) discussed the evolution and distributional history of Quercus, and this has been the focus of much recent work; Cavender-Bares (2018) provides an extensive discussion of the ecology and evolution of American oaks which is of considerable general interest. Fossil acorns of Quercus in particular are known from ca 44 Ma deposits in Oregon (Manchester 1994), but there are probably older fossils (fossil pollen to ca 56 Ma) that can be placed here - see in particular Hofmann et al. (2011b), Barrón et al (2017), also Mensing (2014: California oaks). The basic diversification patterns in the genus seem to be first, geographical, and second, ecological (Hipp et al. 2019). Quercus is made up of an Old World/mid-latitude and a New World/high latitude clade, with divergence between the two beginning in the later Eocene (Hubert et al. 2014; Deng et al. 2017: crown-group age (39.2-)35.9(-34.1) My). By the end of the Eocene Fagaceae with sclerophyllous foliage had evolved in western North American, where conditions were more or less seasonal, and Quercus grew then in vegetation that is similar to modern chaparral and nemoral forest; ecologically similar Fagaceae evolved somewhat later and independently in Europe where Mediterranean conditions developed only in the Pleistocene (Bouchal et al. 2014). The greatest diversity of Quercus in the New World is in southern Mexico, Mexico as a whole having around 154 species; within subgenus Quercus, clades of white (section Quercus) and red (section Lobatae) oaks have diversified rapidly there within the last 23 Ma, indeed, their rates of diversification are comparable with the highest estimates in any other plants (Hipp et al. 2017; for white oaks, see also Fitz-Gibbon et al. 2017; McVay et al. 2017b) - and note that species numbers in both Mexican and Central American oaks may be underestimates (Hipp et al. 2019). Rodríguez-Correa et al. (2015) studied niche divergence in species from Mexico and Central America, suggesting that it was affected by various barriers to dispersal. In a comprehensive study of New World taxa, Hipp et al. (2017) linked speciation to parallel sympatric diversification of the two major North American sections responding to moisture gradients, etc. (for parallel evolution of leaf form, see also Tucker 1974). There were 23 or more origins of the deciduous habit, "niche" convergence par excellence, and both red and white oaks have deciduous species with lobed leaves in small basal clades (Hauser et al. 2017; McVay et al. 2017b). In the Old World, species of Quercus subg. Cerris sect. Cyclobalanopsis in particular are common dominants of drier sites in warm temperate to tropical lower montane forests in East Asia (some 60 species in southwest China and northern Indo-China - Deng et al. 2017) and in West Malesia (Ashton 2014). Divergence here began around 26.3 Ma, being shaped by the tectonic/climatic changes in Southeastern Asia (Deng et al. 2017). Simeone et al. (2018) discuss the diversification of oaks of section Cerris in western Eurasis. Section Ponticae (subgenus Quercus) includes only two species, Q. sadleriana, from west North America and Q. pontica, from N.E. Turkey-Georgia. Overall, there are four main increases in diversification rates: The Eurasian white oaks of the Roburoid clade of section Quercus, the sympatric diversification of red and white oaks in North America, and the Eurasian section Cyclobalanopsis (Hipp et al. 2019).
But the back stop of stories such as those just discussed is very complex, with hybridization and introgression common in Quercus in particular. For example, Simeone et al. (2018) note that in species of section Cerris from western Eurasis; here, as elsewhere in the genus (e.g. McVay et al. 2017a), there has been/is currently extensive hybridization, especially in the chloroplast genome, including in this case with species from section Ilex, and the latter group has chloroplasts from five different sources (Simeone et al. 2017). There has been some ancient hybridization between Californian tree and scrub oaks (B. Y. Kim et al. 2018) and between oaks in eastern Europe (Curtu et al. 2007), although without much effect on species identity. Interestingly and importantly, Hipp et al. (2019) note that particular genes or regions of the genome that might help recover the phylogeny of Quercus as a whole were not to be found, "rather, the phylogenetic history of oaks is defined by different genes in different lineages, making [the] evolutionary history of oaks a phylogenetic and genomic mosaic" (see also Hipp 2019) - rather comparable to what one might say about morphological phylogenetic reconstructions...
Oh and Manos (2006, 2008) suggested that the scaly or spiny cup-shaped cupule that encloses a single, rounded fruit, the acorn, has evolved more than once within Quercoideae, while Cannon and Manos (2001) looked at the evolution of the fruits of a few species of Malesian Lithocarpus in which a woody receptacle almost entirely surrounds the fruit (enclosed receptacle(ER)-type fruits - sort of like a cactus fig), rather than being a circular structure at the base, and the smooth, shiny wall of an ordinary acorn (exocarp) is very reduced; the fossil Cascadeicarpa has a similar "doubly inferior ovary" (Mindell et al. 2007: G ). X. Chen et al. (2012) noted that ER fruits tended to have more structural carbohydrates than acorn-type fruits, which had more indigestible (to a small mammal) fibres, although the sample size was small and how such differences actually worked out in the field unclear.
Renner et al. (2016) discuss diversification within Fagus where, as in Quercus, there is a major split correlated with geography, if complicated by fossil distributions; speciation here is slow, F. grandifolia being the only member of a ca 45 Ma lineage.
Ecology & Physiology. Fagaceae are often very common in north temperate areas and they are also common and notably diverse on hills and mountains in Mexico and Central America and Malesia. The family frequently dominates the vegetation in which it grows, taxa like Castanopsis acuminatissima being conspicuous in montane vegetation as far east as the island of Papua. Along with Magnoliaceae, Theaceae and Lauraceae (Tang 2015; Yu et al. 2017), they are a notably prominent component of the temperate and subtropical evergreen broad-leaved forests (EBLFs) of East Asia, and their effect on the community is increased by the sometimes rather sporadic episodes of heavy fruiting that are more or less synchronized over quite wide areas, mast fruiting (see below). Fagaceae are an important element of the diet of many animals, including the now-extinct passenger pigeon (Ectopistes migratorius) in North America (Halliday 1980). The demise of the passenger pigeon, which once made up 25-40% of the total avian biomass in North America, may have been hastened in part by the destruction of its food sources as settlers cleared woodlands for agriculture. Fagaceae - oaks, beech, chestnuts - were a major element in its diet (Curran & Leighton 2000 and references).
White oak (Quercus alba) alone represents (12-)19-26(-49)% of witness trees, i.e. trees that were probably present before Europeans arrived, in the oak-dominated forests of eastern North America (81% in some southern Illinois forests). In such forests, (36-)50-80(-± 100)% of all trees are white oak, along with with up to three more ectomycorrhizal (ECM) species, two of which are usually other Fagaceae (Abrams 2003; see also Faison & Foster 2014). Six of the 30 species of Quercus growing in these forests are notable dominants (Abrams 1996). Many oaks like high light and moderately dry conditions, and fires are quite common; oak can replace pine in such situations (Adams 1992; Mensing 2014). Fagaceae, again mostly Quercus, are abundant in western North America, and in California the black oak, Quercus kelloggii, is particularly widespread and has the greatest timber volume of any oak (Waddell & Barrett 2005). Papers in Gil Pelegrín et al. (2017) discuss the ecophysiology of oaks.
The ECM American chestnut, Castanea dentata, previously a dominant large tree in some forests in eastern North America and an important timber tree and source of food for humans and other animals, now persists largely as suckers after its devastation by chestnut blight in the first half of the last century (Thompson 2012: dominant over 800,000 km2), however, Faison and Foster (2014) qualify literature reports, i.a. noting that some of the dominance of chestnut was quite recent, being accentuated by coppicing after being cut down by early Europeans (see also Russell 1987). In any event, much of the chestnut forest has since been replaced by mixed oak or oak-hickory forests (Abrams 1996; see e.g. van der Gevel et al. 2012 for the future), so the forests remain dominated by ECM trees.
Oaks or beech are major components of oak/bamboo forests, the bamboo making up the understory, in many parts of the world, although such forests are not to be found in Europe and much of temperate North America (Kappelle 2006b). Fagus-dominated forest may have very little in the way of understory vegetation.
In holm oak, Quercus ilex, the adaxial surface of the leaf is wettable and can absorb water, the lower side is densely covered in trichomes and is not wettable, so preserving stomatal functioning in wet conditions (Fernández et al. 2014) - see also Bromeliaceae.
In an examination of the genome of Quercus robur in the context of trying to understand the longevity of oak trees, the accumulation of somatic mutations, the expansion of R genes involved in immune defeence, and the diversification of defence genes were all noted - and much local and recent gene duplication was also observed (Plomion et al. 2018). Of course, similar connections are to be expected in long-lived trees in general (Tobias & Guest 2014).
Pollination Biology & Seed Dispersal. Quercus and Fagus are wind pollinated, otherwise, insect pollination dominates in other clades in the family (Cannon 2019). Fertilization is porogamous, according to Johri et al. (1992), although it can be much delayed (Sogo & Tobe 2006d and references; Deng et al. 2008). X.-R. Yang et al. (2017) discuss variation patterns in various floral/reproductive features in the family; they suggest that the pollen tube normally is dormant for a while in the style, but in the funicle/integument in Fagus.
Some Fagaceae simultaneously, if somewhat erratically, produce large numbers of fruits over large areas, the phenomenon of masting; for accounts of this synchronized but intermittent fruiting, see Koenig and Knops (2000, 2005) and Koenig et al. (2017). The trigger of a masting event is often an environmental cue, in at least some species studied replenishment of reserves after a masting period being unnecessary (Bogdziewicz et al. 2019). The effect of masting on the animals that eat these fruits is considerable (Koening & Knops 2005). As with the mast-fruiting dipterocarps, q.v., some of the seed predators like passenger pigeons (Ectopistes migratorius: see above) in eastern North America and wild pigs in Europe are (or were) migratory. For fruit dispersal and habitat preferences, see X.-G. Xiang et al. (2014: Fagus with winged fruits; c.f. Mindell et al. 2009; Larson-Johnson 2015).
Somewhat complicating the masting story, it is well known that fruits of red oaks (subgenus Quercus, section Lobatae) take one and a half years to mature ("2-year species"; also some species of Castanopsis and Lithocarpus), overwintering as very small embryos, or fertilization may not occur until the spring after flowering (Stairs 1964; Sork et al. 1993; Borgart & Nixon 2003). Interestingly, a number of species of red oaks in Mexico and Central America can mature acorns in under a year - evolutionary reversal (Nixon 2006), while up to four years between pollination and seed maturity may elapse in species of section Ilex (M. Deng, in Denk et al. 2017) - indeed, it may not be easy to recognize biennial maturation patterns (Denk et al. 2017). Most 2-year species produce new shoots every year, and so have acorns each year (consecutive-bearing species), while others, especially in Quercus subgenus Cyclobalanopsis, are alternate-bearing species that produce shoots, and so acorns, only every other year (Hirayama et al. 2019: see below for possible connections with a weevil seed predator).
The seeds of mature acorns of two-year red oaks are high in tannins and lipidsThe fruits of white oaks (section Quercus) mature in about six months and their seeds are less rich in tannins and lipids, furthermore, their seeds tend to germinate faster. Much has been written about the behaviour of animals that currently eat and disperse the acorns of these species. Thus squirrels tend to eat the embryos of white oaks before caching the fruits; in general they prefer to eat acorns of white oaks in the fall and to cache those of red oaks (Smallwood et al. 2001; Wood 2005 for literature), although in non-masting years there may be no difference in animal behaviour (López-Barrera & Manson (2006). In general, it is the state of germination of the seed that most affects the behaviour of acorn dispersers - what they eat, where they cache - so germinating red oaks are treated in the same way as germinating white oaks (Smallwood et al. 2001). However, seedlings of white and red oaks differ, those of the former being largely subterranean in the first autumn of their existence, most of the seed reserves being transferred into their large taproot, the plumule appearing in the next year, while red oak seedlings germinate in a more conventional way - all these differences potentially translate into differing rates of spread of species of the two groups, perhaps different reactions to soil fungi, etc. (Steele & Smallwood 1994; Smallwood et al. 2001). For the growth of oak seedlings with and without their cotyledons and their response to damage/herbivory, see Gelviz-Gelvez et al. (2017).
Plant-Animal Interactions. Fruits of Fagaceae are a major source of food for a diversity of animals (see also above). These include birds like the acorn woodpecker, Melanerpes formicovorous - Koenig et al. (2017, see also 2014) have a remarkable photo of the 000's of acorns the birds have cached in the bark of an oak tree - squirrels, pigs, etc., although the relationships of the two parties are rarely obligate.
Oaks support the highest diversity of herbivores of all temperate holarctic forest trees. Theclines (Lycaenini) caterpillars are common on Fagaceae (Ehrlich & Raven 1964), while leaf-mining larvae of Eriocraniidae, probably the subbasal clade in the lepidopteran Angiospermivora, eat Fagaceae and Betulaceae (Regier et al. 2015 and references). Pearse and Hipp (2012) found that leaf defences in Quercus were highest at lower latitudes (little temperature fluctuation, mild winters, low minimum precipitation).
Some evergreen species of Quercus subgenus Cyclobalanopsis are alternate-bearing species that produce shoots, and so acorns, only every other year (Hirayama et al. 2019). This odd behaviour is apparently connected with the attentions of the weevil Mechoris ursulus which lays its eggs in mature acorns (it chooses the largest acorns) and then cuts off the twigs on which the acorns are growing, this part of the whole process taking about a week; the mature larvae leave the fallen acorn that same year and then overwinter underground - so, remarkably, the weevil is also a two-year species, unusual for a weevil (Koo et al. 2002; Hirayama et al. 2019). These Cyclobalanopsis oaks lose only one year's growth/one crop of acorns. However, this is not the whole story, for instance, the weevil also lays aggs on other two-year species which are consecutive-bearing, bearing shoots and acorns every year, and here the weevil cuts off two years' growth and the plant loses two seasons of acorns; these species are deciduous... (Hirayama et al. 2019).
By some estimates half of all galls in the north temperate region are found on Fagaceae, especially on oaks, and perhaps especially in North America, where Quercus is particularly diverse (Mani 1964; Abrahamson et al. 1998; Oyama et al. 2006: galls in Mexico). Galls produced by gall wasps (Cynipini) are common on oaks, and they differ in morphology depending on whether they are produced by sexual or agamic individuals; leaves, twigs, fruit, even roots may all be galled, and the resultant overall morphological diversity of galls is remarkable (Redfern 2011). The some 1,000 species of gall wasps are perhaps two thirds of the known species in the whole Cynipidae, while quite a number of species are inquilines, laying eggs in galls made by other species (Csóka et al. 2005; Stone et al. 2009). Host plant conservatism here has persisted over the last ca 20 Ma at least, and major clades of gall wasps are usually associated with major clades of oaks (Cook et al. 2002; Stone et al. 2009; Leckey & Smith 2015).
Ants - the species were largely the same as those visiting extrafloral nectaries - were notably common visitors to sap exuding from wounds on leaves of Fagaceae in subtropical S.E. China (Staab et al. 2017: planted forests). Interestingly, extrafloral nectaries are uncommon in Fagaceae, and one might think that it was not surprising that the frequency of ant visits increased with the severity of leaf damage - but this was not true of other species of plants visited by the ants (Staab et al. 2017). For wound-type extrafloral nectaries, see also Solanaceae-Solanum.
Bacterial/Fungal Associations. Chestnut (Castanea dentata) forests were utterly devastated by the introduced ascomycete fungus Cryphonectria parasitica (Endothia parasitica in older literature) over a period of less than forty years, 1904-1940 (Hepting 1974; H. Thompson 2012). Although chestnut plants can persist in the understory for many years after initial infection because they sucker from collars of the dead old trees or from stumps, the suckers practically never reach reproductive age before being reinfected by the fungus (Schlarbaum et al. 1997).
Sudden oak death, caused by the oomycete Phytophthora ramorum has beome a major pathogen on Fagaceae in coastal California and in Oregon over the last 20 years or so, and the infestation is out of control (Cunnliffe et al. 2016). Indeed, oak decine is widespread, and fungi like Ceratocystis fagacearum and Diplodia (both ascomycetes, unrelated) are involved in oak wilt diseases in particular (Rodríguez-Calcerrada et al. 2017), and these authors make it clear that in such diseases many factors interact - human activities in forests, herbivory by insects and other animals, climate, decreasing rainfall, the activities of microbes - and symbionts can become parasites. There are also other unpleasant oak pathogens like the ascomycete Raffaela quercivora that is associated with ambrosia beetles (weevils) which obligately cultivate fungi (Huler & Stelinski 2016; see also Jordal & Cognato 2012, Pinaceae, and papers in Vega & Hofstetter 2015).
Kühdorf et al. (2015: p. 110) noted that the arbutoid "C[omarostaphylis] arbutoides is a refuge plant for ectomycorrhizal fungi as it shares these fungi with ectomycorrhizal tropical trees such as Quercus costaricensis". Interestingly, in temperate North America Quercus is reported to be both an ECM and an arbuscular mycorrhizal plant (Bennett et al. 2017: Supplementary Material).
Genes & Genomes. For genome sizes in the family, see Chen et al. (2014). Although it was suggested that tropical species generally had larger genomes than temperate species, the smallest genomes were found in temperate species (Fagus, some species of Quercus: S.-C. Chen et al. 2014).
A mitochondrial gene has moved from the parasite Mitrastemon (Ericales) to its host, Quercus (Systma et al. 2009).
For intergeneric and intersubfamilial graft hybrids, see Herrmann (1951).
Chemistry, Morphology, etc.. Syllepsis is very uncommon in the family (Keller 1994). For leaf vernation, see Couturier et al. (2009, 2011).
For general inflorescence morphology in Fagaceae, see Kaul and Abbe (1984). There has been much discussion over the morphological nature of the small protrusions surrounding the ovary, and the whole complex is often interpreted as a modified cymose inflorescence (e.g. Forman 1966a; Sims et al. 1998; Manos et al. 2001a; Pigg et al. 2001; Oh & Manos 2008 for references; c.f. Jenkins 1993: modifications of the perianth). When the cupule has valves, probably the plesiomorphic condition, there is one valve more than the number of fruits; the valves represent modified cymose part inflorescences (Fey & Endress 1983).
Endress (1979a) suggested that the flowers of Fagaceae were hexamerous. For the orientation of the carpels, see Endress (1977a) who shows the median member of outer T whorl in both staminate and carpelate flowers as being abaxial (c.f. Sims et al. 1998). Denk and Grimm (2009b) describe pollen morphology with a focus on Quercus; I use their terms above (see also Praglowski 1982, 1984); Denk and Tekleva (2014) think about foot layer variation (see also Grímsson et al. 2016: thick foot layer plesiomorphic in the family). Variation in ovule and fruit is extensive, and is conveniently tabulated by Deng et al. (2008); the polarity of some of this variation is unclear. X.-R. Yang et al. (2017) suggest that the endocarp of Fagus lacks trichomes, Kubitzki (1993b) that it has them. Hjelmqvist (1953) discussed the basi-lateral embryo sac/endosperm caecum he noted in some Quercoideae.
See also Nixon (1989, 2006) and Kubitzki (1993b), general, Hegnauer (1966, 1989: chemistry), Loreto et al. (2009: monoterpenes, isoprenoids in Quercus), Huang et al. (2011: ellagitannins with triterpene alcohol cores), Clowes (1951: anatomy of mycorrhizae), Whitmore (1963: bark), Lersten and Horner (2008b: leaf crystals, etc.), Liu et al. (2009: stomata, hairs), Crepet and Daghlian (1980: pollen) and Langdon (1939: ovules, etc.) for additional information.
Phylogeny. Fagus is sister to all other Fagaceae (Manos et al. 1993; Sauquet et al. 2012); Quercoideae s. str. are paraphyletic, Trigonobalanus being sister to the rest of the clade. For phylogeny see also Manos and Stanford (2001), Manos et al. (2002) and X.-G. Xiang et al. (2014). Li (1996) did not find Fagaceae to be monophyletic in his morphological analysis.
Renner et al. (2016) discuss relationships in Fagus.
Trigonobalanus had long been known from Fraser's Hill in Peninsula Malaya, but was first described some 55 years ago from Mt Kinabalu in Borneo (Forman 1964), a species from was included, it was then found in South America 35 years ago, and then fossil in North America... (Nixon & Crepet 1989 for information). X.-G. Xiang et al. (2014) found that support for the position of Trigonobalanus was not that strong and Quercus was paraphyletic - or at least its monophyly was unclear, and similar relationships are still sometimes found in plastome analyses (X. li et al. 2018; Xuan et al. 2018; Ye et al. 2019) although as Simeone et al. (2016) and others have pointed out, confused relationships are caused by hybridization and plastid introgression. Oh and Manos (2006, 2008) suggested that Lithocarpus, which has fruits like those of Quercus, is polyphyletic, the South East Asian members grouping with Chrysolepis. Indeed, the single species from the Californian floristic province of West North America, L. densiflorus (now = Notholithocarpus), is in a clade with Quercus, Castanopsis, and Castanea. For relationships in Vietnamese oaks, Quercus and Lithocarpus, see Strijk and Hinsinger (2019: phylogenomics), the sections in the latter in particular are more or less wildly polyphyletic.
Quercus contains both species with fast-maturing (a few months) acorns and a pericarp that is glabrous inside - both derived characters - and species in which the acorns take 1 1/2 years to develop and the endocarp is hairy inside. For phylogenetic relationships within Quercus, see Manos et al. (1999), Oh and Manos (2008) and especially Hubert et al. (2014). However, detailed relationships may be difficult to disentangle if the various positions that different accessions of species like Q. ilex, Q. suber and Q. robur appear on the one tree is any indication (Simeone et al. 2013); relationships were also affected by the outgroup chosen (Hubert et al. 2014). For relationships in North American oaks, see Manos et al. (1999), Pearse and Hipp (2009) and Hipp et al. (2014); McVay et al. (2017a, b) discuss the influence of hybridization/introgression on our understanding of relationships in the speciose section Quercus. Hipp et al. (2017) have produced a well-sampled and well-resolved phylogeny for North American oaks (see also above), sections Protobalanus and Pontica (see above) are basal in subgenus Quercus, and general relationships in the genus are becoming resolved (Hipp et al. 2019: see also above). For relationships in the speciose Southeast Asian Quercus section Cyclobalanopsis (subgenus Cerris) see Deng et al. (2013, especially 2017).
Classification. Govaerts and Frodin (1998) provide a now rather dated checklist and bibliography for the family. The three extant species of Trigonobalanus have been placed in three genera, but they form a single clade; one genus or the three is fine. For an infrageneric - two subgenra, 8 sections - classification of Quercus, see Denk et al. (2017); distinguishing characters are mentioned.
[[Myricaceae + Juglandaceae] [Casuarinaceae [Ticodendraceae + Betulaceae]]] / the Normapolles group: myricetin +; (N-fixing Frankia +), (cluster roots +); pollen tripororate, exine of two layers separated by an alveolar zone and obviously expanded around the apertures, exine infratectum granular, intine thickening at the apertures [= oncus] [?level]; G ; funicle not evident; fertilization chalazogamous.
Age. This node has been dated to 47-46 Ma (Wikström et al. 2001), (50-)41, 37(-28) Ma (Bell et al. 2010), or as early as (96.9-)93.4(-88.2) Ma (X.-G. Xiang et al. 2014, but c.f. topology) and, similarly, ca 93.6 Ma in X.-Y. Yang et al. (2018).
Evolution: Divergence & Distribution. For variation patterns in various floral/reproductive features, see X.-R. Yang et al. (2017).
The pollen of Betulaceae and Juglandaceae in particular is rather like that of the fossil Normapolles type, and they all have a granular exine infratectum (e.g. Doyle 2009); see Christopher (1979) and Batten (1980) for the classification of these grains, also papers in Rev. Palaeobot. Palynol. 35(2-3). 1981. Batten (1989; see also Clarke et al. 2011) was cautious about the organismal connections of these grains, not all of which may have come from members of Fagales, and the grains did not always seem to him to be of wind-pollinated plants (Batten 1981). As he observed, "In due course it may be reasonable to refine the Normapolles as a distinct pre-juglandalean/myricalean order for plants which produced pollen grains of the Trudipollis-Oculipollis type and morphologically comparable forms" (Batten 1989: p. 19), and he even thought that Betulaceae, for instance, might not have Normapolles-producing ancestors. Polette and Batten (2017) have begun the task of clearing up the synonymy (13 genera were synonymized) by trying to identify the names, noting "for many [species] this required interpretations of obscure descriptions often full of unnecessarily complicated terminology describing features that are commonly unrecognizable in the accompanying figures" (ibid.: p. 89). Further confusing the issue, Larson-Johnson (2015) placed a number of fossils purportedly of Normapolles-producing plants outside crown-group Fagales. Odd character combinations in pollen of late Campanian/early Maastrichtian age ca 70.6 Ma have even been explained as the result of hybridization (Hofmann et al. 2011b). Normapolles-type grains have also been compared with those of Urticaceae and relatives and Proteaceae (Batten 1981), while Feuer (1991) did not find much similarity between the pollen of many extant members of this clade.
There is much variation in Normapolles-producing fossil flowers (see Friis et al. 2006a, especially 2011: e.g. chap. 14.6.6, Fig. 20.6, etc.), and new genera are still being described. The flowers are usually perfect and with a simple, undifferentiated perianth. Thus Zlivifructus has perfect flowers, an inferior 2-carpelate gynoecium with a hypanthium, four perianth members in pairs and four stamens, while the fruit has a single, erect, straight seed (Hermanová et al. 2017). Caryanthus has a four-parted perianth with six stamens in two groups of three (Sims et al. 1999: Table 2). Normanthus, from the late Cretaceous of Portugal, has five quincuncial perianth members that alternate with the stamens, and there are two collateral carpels with separate and quite long styles; the placentation is described as being parietal, with one ovule/carpel (Schönenberger et al. 2001b). Dahlgrenianthus has five stamens opposite the perianth members and a superior ovary with short, more or less separate styles (Friis et al. 2006a). Endressianthus has imperfect flowers, with four stamens alternating with the perianth members (Friis et al. 2003a), while in Bedellia staminate flowers only are known, and these have two five-parted perianth whorls. As with other fossil Fagales (see above), relating these fossils to extant families is a challenge.
That being said, Normapolles pollen was abundant in the Turonian-Campanian of the Cretaceous, some 94-80 Ma, peaking in the Coniacian-Santonian ca 88 Ma, and occurring in much of the Northern Hemisphere in the area 20-45oN (Cretaceous palaeolatitude) from west Siberia to east North America in particular (Kedves & Diniz 1983; Kedves 1989; Sims et al. 1999; Friis et al. 2003a, esp. 2006a, 2011: Figs 20.6, 7 for summaries); Aquilapollenites, variously linked with Santalales (e.g. Jarzen 1977), Apiaceae, and Caprifoliaceae-Morinoideae, is found in between this area and it is also circumboreal (Vakhrameev 1991; Farabee 1993). Trees that perhaps produced Normapolles pollen may have dominated open late Cretaceous (Campanian) woodland in Texas (Lehman & Wheeler 2001), but this needs confirmation. Normapolles disappeared from the fossil record at the Eocene-Oligocene boundary, although the pollen of Rhoiptelea (Juglandaceae) is very Normapolles-like (Traverse 1988).
Details of wood anatomy, including the presence of chambered crystals in the axial parenchyma, that are common in this group (Carlquist 2002c) may properly be features of Fagales as a whole.
Ecology & Physiology. Taxa that have cluster roots, usually associated with an enhanced ability to take up phosphorus, and that are also associated with N-fixing bacteria, are scattered through this clade (Myricaceae, Casuarinaceae, Betulaceae-Alnus: Dinkelaker et al. 1995; Lambers et al. 2008).
Chemistry, Morphology, etc.. Normapolles pollen is oblate in shape and triaperturate with protruding, elaborate and strongly thickened apertural regions, the apertures themselves often being formed from expansions of the granular infratectal layer (see also Feuer 1991); the result is that the pollen is more or less triangular in transverse section. The apertures have internal pores and externally short colpi or pores. The wall is usually tectate-granular, but there is sometimes an atectate polar zone, the surface being almost smooth to finely spinulate to rugulate. The infratectum is granular (details from Friis et al. 2003a).
[Myricaceae + Juglandaceae]: chains of crystal-containing cells in the wood; sieve tube P-protein bodies 0; peltate glandular hairs +; stipules 0; 1 flower/bract; stigma lamellular/laciniate; ovule single [per flower], straight, erect, integument entirely free from nucellus; x = 8, longest chromosome with (sub)median secondary constriction.
Age. This node has been dated to ca 47.1Ma by Tank et al. (2015: Table S2), 38-36 Ma (Wikström et al. 2001) or (43-)32, 29(-11) Ma (Bell et al. 2010), but see other dates below.
The age of a node [Myricaceae + The Rest] is estimated at (94.6-)90.4(-85.0) Ma (X.-G. Xiang et al. 2014, see topology).
Evolution: Divergence & Distribution. The evolution of features of inflorescence and ovule is particularly difficult to understand; they could be synapomorphies of the clade as a whole (as above), or be independent apomorphies of Myricaceae and Juglandaceae-Juglandoideae. Herbert et al. (2006) discuss possible synapomorphies around here.
Chemistry, Morphology, etc.. The leaf teeth in Myricaceae in particular, see also Cuinoniaceae, etc., are intermediate in "type" and venation characters do not distinguish sharply between Cunoniaceae and Fagales (see Hickey & Taylor 1991).
MYRICACEAE Kunth, nom. cons. - Back to Fagales
Plants dioecious or monoecious; staminate flowers: A (opposite P); carpelate flowers: G [(3)], ?superior to inferior; ovule basal; fruit a drupe; seed ?pachychalazal, testa ± thickened; endosperm slight or 0; n = 8, 12.
4 [list]/57: two groups below. ± Cosmopolitan, scattered (map: Hultén 1958; van Balgooy 1974; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010).
Age. An age of (81.7-)69.7(-60.4) Ma for crown-group Myricaceae is suggested by X.-G. Xiang et al. (2014).
Fossil pollen attributed to the family is Cretaceous-Cenomanian (97.5-91 Ma) in age (H.-L. Li et al. 2015).
1. Canacomyrica Guillaumin
?Nodes; P connate, 6-lobed; staminate flowers: A 6; pistillode +; carpelate flowers: staminodes +; ovule ?bitegmic, micropyle much elongated; ?fertilization; in fruit micropyle becoming still more elongated, recurved.
1/1: Canacomyrica monticola. New Caledonia (map: green).
Synonymy: Canacomyricaceae Doweld
2. The Rest.
(Plant deciduous); cluster roots +, N-fixing Frankia +; nodes also 1:1; lamina (pinnatifid), vernation conduplicate to curved or revolute, (?stipules foliaceous, lobed - Comptonia); P 0; staminate flowers: A 2-8(-20); carpelate flowers: staminodes 0; ovule quite well developed at pollination, unitegmic, integument vascularized, 3-7 cells across, parietal tissue 4-9 cells across, nucellus apex exposed/not, central strand in supra-chalazal tissue; megaspore mother cell single; fertilization porogamous.
3/55: Morella (46). ± Cosmopolitan but scattered, not in the southern half of South America nor south and east of New Guinea (map: above, red). [Photos - Collection.]
Age. The crown-group age of this clade is estimated at around 24.9 Ma (Sauquet et al. 2012), (58.6-)54.3(-49.6) Ma (X.-G. Xiang et al. 2014), or (95.7-)71, 69.8(-55.1) Ma (H.-L. Li et al. 2015).
Evolution: Divergence & Distribution. Comptonia, now restricted to eastern North America, was widespread in the Northern Hemisphere (including Greenland) in the Caenozoic, with some records dating from the Late Cretaceous; most of the records are of the distinctive foliage (Liang et al. 2010). Canacomyrica, now endemic to New Caledonia, has been reported from New Zealand as recently as 17-11 Ma (D. E. Lee et al. 2001) while fossil myricaceous pollen is known from S.W. South Africa in deposits ca 15 Ma (Coetzee & Praglowski 1984).
Ecology & Physiology. Myricaceae - but not Canacomyrica - are associated with N-fixing Frankia and cluster roots are also developed; mycorrhizae appear to be absent (Hurd & Schwintzer 1997). Carboxylate exudation may help in phosphorus acquisition (Lambers et al. 2012b).
Pollination Biology & Seed Dispersal. Although fertilization is porogamous, it is somewhat delayed, rather as in other Fagales. The pollen tubes pause in their growth on the nucellar surface, which is at least initially exposed (according to some accounts), and this pause has been compared with the pause at the chalaza that occurs in other members of this clade; this method of fertilization has been called pseudoporogamy and may be derived (Sogo & Tobe 2006a, b: ?two characters - micropyle +/0, pollen tube enters the ovule through the micropyle). The flowers of plants of some species differ in sex from year to year (Jurzyk 2005 and references).
Bacterial/Fungal Associations. Both AM and/or ECM associations have been reported from Myricaceae (e.g. Rose 1980).
Chemistry, Morphology, etc.. Hickey and Taylor (1991) showed a leaf of Canacomyrica in which two adjacent teeth were cunonioid and rosid respectively.
Bracteoles may be present or not. Although the ovary appears to be superior, as in Comptonia, it is often so highly reduced that any traces of its inferior construction would be lost, however, in Canacomyrica, from New Caledonia, staminodes are borne on top of the ovary and there is a six-lobed perianth. In some species of Myrica the ovary is invested by tissue from a meristem developing below the flower, even below the bracteoles, which are then borne on the flower (Kershaw 1909). The flowers of Canacomyrica have three "bracts" (Herbert et al. 2006) - do these represent a floral bract plus two bracteoles/prophylls? Kubitzki (1993b) draws the ovule of Canacomyrica as being basal, straight, and with a much elongated integument forming an apical tube (see also Macdonald 1989); Herbert et al. (2006) simply describe the ovules as being bitegmic.
For general information, see Kubitzki (1993b), for chemistry, see Hegnauer (1969, 1990), for wood anatomy, see Carlquist (2002c), for floral morphology, very tricky to interpret, see Macdonald (1978, 1979 and references) and Leroy (1957: Canacomyrica), for pollen, see Coetzee and Praglowski (1984), for ovules and fertilization, see Kershaw (1909).
Phylogeny. Relationships within Myricaceae are likely to be [Canacomyrica [Comptonia + The Rest]] (Herbert et al. 2006; X.-G. Xiang et al. 2014: support strong; M. Sun et al. 2016), which, depending on the phylogeny of the order, could have interesting implications for character evolution. Huguet et al. (2004) found the relationships [[Myrica + Comptonia] other Myrica], the two clades being colonized by different strains of Frankia.
Classification. If the topology of Huguet et al. (2004) holds, then the limits of Myrica will have to be either expanded or contracted.
JUGLANDACEAE Perleb, nom. cons. - Back to Fagales
Xylem with gelatinous fibres; buds lacking scales; leaves compound, odd-pinnate; P 4; pollen scabrate; carpels median, apically 1-locular, stigmas decurrent, ± recurved; endosperm 0.
9 [list]/51, three groups below. North temperate, also Malesia and the Andes.
Age. Crown-group Juglandaceae are estimated to be around 85.8 Ma (Sauquet et al. 2012) or (96.4-)79.9-(71.2) Ma (X.-G. Xiang et al. 2014; see also J.-B. Zhang et al. 2013).
1. Rhoipteleoideae Reveal
Plant deciduous; chemistry?; cork?; sieve tube protein bodies?; leaves two-ranked, leaflets alternate, stipules +, asymmetrically caudate; inflorescence branched-catkinate; flowers in triads, central flower perfect; A 6; pollen 3-colporate, ectoapertures elliptic, exine folded [plicate], vestibulum 0, endexine lamellate, thick at the apertures; G, adaxial fertile, stigmas commissural, flattened; ovule campylotropous, bitegmic, micropyle endostomal, outer integument ca 4 cells across, inner integument 4-5 cells across, parietal tissue 2-5 cells across, ?suprachalazal tissue; ?fertilization; fruit a samaroid nut; P persistent; testa?; n = 8; ?seedling.
1/1: Rhoiptelea chiliantha. Southwest China, northern Vietnam (map: from Fu 1992).
Synonymy: Rhoipteleaceae Handel-Mazzetti, nom. cons.
[Engelhardtioideae + Juglandoideae]: flavones, naphthoquinones [inc. plumbagin], raffinose and stachyose [phloem exudate] +; xylem with banded parenchyma; nodes also 5:5; leaves spiral, leaflets subopposite, (margins entire); (inflorescence branched); (P 0-3); staminate flowers: A 4-many; pollen 2-20 porate, apertures usu. elongate, endexine homogeneous, not at the apertures; pistillode +; carpelate flowers: ?staminodes; [(G 3, 4)], when 3, median member adaxial, loculi ± divided [false septum], (stigmas not decurrent), (commissural); ovule borne at the top of the septum, erect, integument 6-10 cells across, (lobed), parietal tissue 3-11 cells across; megaspore mother cells numerous; (fertilization porogamous); fruit drupaceous, nut, samaroid, or winged by persistent bracts, pericarp intrusive; seeds (large [>1.5 cm long]), pachychalazal; endosperm very slight or 0, cotyledons much folded; genome duplication, x = 16, second longest chromosome with (sub)median secondary constriction.
Ca 8/50. North temperate, S. to Argentina and Malesia. [Photo - Collection.]
Age. The crown group is around 77.1 Ma (J.-B. Zhang et al. 2013), 72.6 Ma (Sauquet et al. 2012) or (75.9-)70.6(-64.1) Ma (X.-G. Xiang et al. 2014).
The oldest fossils that have been placed in Juglandoideae are some 98-83 (Budvaricarpus: see Hermanová et al. 2011) or 88-73 (Crepet et al. 2004 for references) or 78 (Manos et al. 2007: the age of Caryanthus) Ma. However, both genera mentioned are placed outside crown-group Fagales(!) in the combined molecular-morphological study of Larson-Johnson (2015).
2. Engelhardtioideae Iljinskaya
Plant (deciduous); vessel elements with simple and scalariform perforation plates; leaf parenchyma with druses [basal condition - none]; leaves (opposite), even-pinnate, leaflets usu. entire, (vernation involute or ± conduplicate - Alfaroa); carpelate flowers: inflorescence catkinate; bracts 3-lobed, bracteoles 0-2, ± abaxial, adnate to lower half of ovary; nuts with a layer of fibrous cells in wall.
3-4/14. Himalayas to Malesia, Mexico to Colombia (map: see Meusel et al. 1965; Manchester 1987).
Age. The crown-group age of this clade is around 36.2 Ma (Sauquet et al. 2012); estimates in J.-B. Zhang et al. (2013) are ca 49.5 Ma, those in Manos et al. (2007) are around 44 Ma and in X.-G. Xiang et al. (2014) are (49.4-)37.7(-28) Ma (see also below).
Synonymy: Engelhardtiaceae Reveal & Doweld
3. Juglandoideae Eaton
Plant deciduous; vessel elements with simple perforation plates alone; (pith chambered); (leaflet vernation involute - Pterocarya); (inflorescence erect and almost cone-like); plant heterodichogamous; staminate flowers: bracts 1-lobed; pollen usu. at least 26 µm across [17-26 µm is the plesiomorphic condition], (4< porate); carpelate flowers: bracts unlobed, bracteoles usually lateral, adnate at least to half the ovary; (G collateral); integument vascularized [?level], (nucellar cap ca 2 cells across); nuts with sclereids in wall, (endocarp with lacunae), (outer part of fruit splitting - Carya); n = (11, 12, 14, 15), polyploidy common.
5/35. Temperate N. hemisphere, only 1 sp. in Europe, Central America and down the Andes, but not native in Brazil (Souza & Lorenzi 2012), c.f. versions prior to vii.2014 (map: see Meusel et al. 1965; Manchester 1987).
Age. Crown-group Juglandoideae have been dated to around 65 Ma (Sauquet et al. 2012), while Manos et al. (2007) gave a range of estimates between about 52 to ca 67 My; there is an estimate of ca 66.6 Ma in J.-B. Zhang et al. (2013) and of (69.7-)66.6(-62.6) Ma in X.-G. Xiang et al. (2014). On the other hand, Bell et al. (2010) suggested that Carya and Juglans (on the two main branches of this clade) diverged only (8-)4(-1) Ma and Wikström et al. (2001) suggested an age of 7-6 Ma.
Polyptera manningii, a well-understood fossil common in what is now S.W. Wyoming as much as 65 Ma, is assignable to Juglandoideae; its pollen is 24-30 µm (Manchester & Dilcher 1997; Donovan et al. 2016). For the placement of other fossils, see Manos et al. (2007); they all ended up in the crown groups of the two subfamilies (J.-B. Zhang et al. 2013).
Synonymy: Platycaryaceae Doweld
Evolution: Divergence & Distribution. A number of extinct genera, some showing very interesting combinations of characters, are known from early Caenozoic deposits in North America, and the family was very diverse there (Manchester 1991; Elliott et al. 2006). Polyptera manningii, a well-understood fossil common in what is now S.W. Wyoming as much as 65 Ma, is assignable to Juglandoideae; its pollen is 24-30 µm (Manchester & Dilcher 1997; Donovan et al. 2016). For the integration of the rich fossil record with the phylogeny of the family, see Manchester (1987), Manos et al. (2007) and particularly Larson-Johnson (2015); all the fossil genera ended up in the crown groups of the two subfamilies (J.-B. Zhang et al. 2013). There are recent reports of Engelhardtioideae (as Alatonucula, also pollen records) from the early Eocene of Patagonian Argentina, far to the south of the current distribution of the subfamily, in deposits at least 47.8 Ma (Hermsen & Gandolfo 2016).
Several extant genera found fossil in North America and especially Europe do not grow there now (Manchester 1987); for the early Caenozoic fossil history of what are now East Asian endemics, see Manchester et al. (1987, 2009). Thus fossil pollen of the monotypic Rhoiptelea, now known from southwestern China and adjacent Vietnam, is found in eastern North America (Fu 1992), while Cyclocarya, now endemic to China, is known pretty much throughout the Northern Hemisphere, the oldest fossils being from Palaeocene deposits in western North America (J.-Y. Wu et al. 2017). Friis et al. (2011) note that some fossils are very similar to Rhoiptelea chiliantha, but they have a half-inferior ovary; the ovary of Rhoiptelea is presumably secondarily superior.
Details of diversification in the family are unclear, and there is great variation in the age estimates for Juglandoideae in particular (Manos et al. 2007). Taxa with biotic dispersal of their seeds may have evolved in the Caenozoic from wind-dispersed taxa (Tiffney 1986a: early Caenozoic; Larson-Johnson 2015: somewhat later). Diversification in the Rhoiptelea clade has decreased (!: Larson-Johnson 2015). Manos and Stone (2001) put morphology in the context of phylogeny.
Ecology & Physiology. Oreomunnea may dominate forests in Panama (references in Peay 2016). Interestingly, it seems that despite strong negative plant-soil feedback at the seedling stage, monodominant stands of Oreomunnea mexicana formed because the ectomyccorhizal fungal associated with the plant could obtain N directly from organic matter (Corrales et al. 2016).
Pollination Biology & Seed Dispersal. There is a form of heterodichogamy in several [Engelhardtioideae + Juglandoideae] (Renner 2001 for references; Fukuhara & Tokumaru 2014). Platycarya (Engelhardtioideae) is distinctive in having sticky pollen and strongly scented flowers, which suggests insect, perhaps thrip, pollination (Li et al. 2005 and references; Fukuhara & Tokumaru 2014).
For fertilization, see e.g. Schanderl (1964), Sartorius et al. (1984), Luza and Polito (1991) and Sogo and Tobe (2008) and references; chalazogamy is not constant in Juglandoideae, and fertilization in Rhoipteleoideae is unknown.
Bacterial/Fungal Associations. Juglans, at least, is not ectomycorrhizal (Tedersoo & Brundrett 2017).
Genes & Genomes. A duplication of the whole genome can be placed at the [Engelhardtioideae + Juglandoideae] node (Luo et al. 2014). For karyomorphology, see Oginuma (1999).
Chemistry, Morphology, etc.. The seedlings of genera with opposite leaves (Alfaroa, Oreomunnea) have spiral leaves.
Triads of flowers are found as abnormalities in the [Engelhardtioideae + Juglandoideae] clade (Manning 1940) and of course they are the normal condition in Rhoiptelea (see above). The fossil Budvaricarpus has similar triade that are surrounded by a common bract (Hermanová et al. 2011). Perfect flowers are known from Platycarya, although normally the cone-like inflorescences have staminate and carpelate flowers mixed; here the bracts are not part of the fruit (Li et al. 2005). For discussion on the nature of the bract/perianth-type structures associated with the flowers, especially the carpelate flowers, see Lin et al. (2016); in Juglans regia, for example, there is a more or less annular rim encircling the carpelate flower, and a bract develops from this in the abaxial position and a single bracteole in a (sub)adaxial position - rather odd.
The staminate flowers of Juglans regia and Engelhardtia spicata are monosymmetric (Lin et al. 2016). The pollen surface is almost microspinulose (Stone & Broome 1975). The stigma may be commissural or not and the orientation of the carpels varies (Manchester 1987; Manos & Stone 2001 - summaries). All three gynoecia of a Budvaricarpus triad are shown as having carpels with the same orientation, although this is supposed to be a cymose unit (Hermanová et al. 2011). Although the ovule of J. regia normally has a single integument, a second integument, probably the outer integument, may also develop (Schanderl 1964).
For general information, see Manchester (1987), Wu and Kubitzki (1993) and Stone (1993), for chemistry, see Hegnauer (1966, 1989), for pollen, see Stone and Broom (1975), for embryology, see Nicoloff (1904) and Boesewinkel and Bouman (1967). For Rhoiptelea in particular: chemistry, see Hegnauer (1990), pollen, see Stone and Broome (1971) and Friis et al. (2006a), embryology, see Z.-Y. Zhang et al. (1994: micropyle described as bistomal, but c.f. micrograph), breeding system, Sun et al. (2006).
Phylogeny. For relationships in the family, see Gunter et al. (1994) and especially Manos and Stone (2001); Engelhardtia is paraphyletic, and monophyly of Engelhardtioideae and Juglandoideae is well supported. Platycarya is often sister to other Juglandoideae, but its position there is not clear (Manos et al. 2007; see also Sauquet et al. 2012; Larson-Johnson 2015). Engelhardtia s. str. is sister to the rest of Engelhardtioideae (Manos & Stone 2001; Manos et al. 2007).
Classification. Including Rhoipteleaceae in Juglandaceae s.l. was optional in A.P.G. II (2003); the two were merged in A.P.G. III (2009).
Manos and Stone (2001) provide a revised classification of [Engelhardtioideae + Juglandoideae], and there have since been adjustments of generic limits.
[Casuarinaceae [Ticodendraceae + Betulaceae]]: dihydroflavonols +[?]; pollen tubes branched; stigmas elongate.
Age. Distributions of ages of this node are bimodal and non-overlapping - some 40.7 Ma in Tank et al. (2015: Table S2), 36-35 Ma (Wikström et al. 2001) and (36-)29, 27(-18) Ma (Bell et al. 2010), or up to 81-71 Ma (Cook & Crisp 2005), ca 87.2 Ma (Sauquet et al. 2012), (88.6-)82.8(-74.7) Ma (X.-G. Xiang et al. 2014) and (97-)92.5, 90(-84.3) Ma (H.-L. Li et al. 2015).
The age in Cook and Crisp (2005) was driven in part by the assignment of the fossil Endressianthus, ca 71 Ma, to the stem of this clade.
Evolution: Pollination Biology & Seed Dispersal. Sogo and Tobe (2008) suggest that the chalazogamous fertilization that occurs in all families of this clade is similar down to the details of where the pollen tube growth is temporarily delayed. Pollen tubes may branch when they have "lost their way" (Sogo & Tobe 2008: p. 624).
CASUARINACEAE R. Brown, nom. cons. - Back to Fagales
Cluster roots +, N-fixing Frankia; flavonols, biflavonoids +, flavones, myricetin 0; banded apotracheal parenchyma +, rays broad, compound (0); cauline endodermis +; cork cambium both superficial (sulci) and deep-seated on the one stem; nodes 1:1, traces originating two internodes below leaf; stem thin, green, photosynthetic, stomata usu. tetracytic [hidden], transversely oriented; leaves 4-16-whorled, scale-like, margins entire, stipules 0; plant monoecious or dioecious, inflorescences capitate-spicate, one flower/bract, bracts and bracteoles ± well-developed; staminate flowers: P 2 ["inner bracteoles"], median; A 1, filament incurved in bud, anthers ± longer than connective, thecae separate or not; tapetal cells uni(bi-)nucleate; pollen infratectum not granular; pistillode 0; carpelate flowers: bracteoles large; P 0; staminodes 0; abaxial G alone fertile, stigma wet; ovules bitegmic, micropyle endostomal or nucellus apex exposed, outer integument 3-4 cells across, inner integument 2-3 cells across, parietal tissue 5-8 cells across, central tracheids in supra-chalazal tissue, vascular bundle branched in chalaza; megaspore mother cells numerous, embryo sacs several, chalazal caecum +, (reaching the funicle); fruit a samara, freed as the much accrescent bracteoles separate; seed coat adnate to pericarp; endosperm 0; n = 8[Gymnostoma]-14; germination epigeal, phanerocotylar.
4 [list]/95. South East Asia and Malesia to the S.W. Pacific, esp. Australia (map: from Coetzee & Muller 1984; Fl. Austral. 3. 1989; fossils blue, see references below). [Photo - Collection.]
Age. The beginning of divergence within Casuarinaceae has been dated to (65.7-)56.2(-45.3) Ma (X.-G. Xiang et al. 2014); material from the Eocene ca 52.2 Ma from Patagonia has been placed in Gymnostoma (Zamaloa et al. 2006).
Evolution: Divergence & Distribution. Casuarinaceae fossils are known from Caenozoic deposits in South Africa, the Ninety East Ridge in the Indian Ocean, Ross Bay, Antarctica, and Argentina (Coetzee & Muller 1984; Coetzee & Praglowski 1984; Hill & Brodribb 2001). Casuarinaceae were especially prominent in the lower Middle Miocene of New Zealand (Lee et al. 2001; Pole 2003; Vanner 2019).
The diversification rate increased in Allocasuarina (Bouchenak-Khelladi et al. 2015), and this may be associated with the aridification of the Nullarbor Plain some 14-13 Ma that separated eastern and western clades (Crisp & Cook 2007).
Ecology & Physiology. A number of Casuarinaceae are halophytes (Moray et al. 2015). There was a switch from scleromorphy (Gymnostoma) to xeromorphy, perhaps some time in the Miocene (Hill & Brodribb 2001).
Nitrogen-fixing is known from the family, and Casuarina oligodon plays an important role in agriculture in parts of montane New Guinea, both in providing firewood and in fixing N for the sweet potato crop (Golson & Garner 1990). Cluster roots, probably enhancing phosphorus uptake, are also common; cluster roots, gram-positive N-fixing actinomycetes, and ECM make a very unusual combination (Shane et al. 2006; Lambers et al. 2008).
Pollination Biology. For the evolution of breeding systems in Allocasuarina, see Goldberg et al. (2017).
Bacterial/Fungal Associations. The receptor-like kinase gene SymRK involved in the common signaling symbiotic pathway is an integral part both of arbuscular mycorrhizal associations and Frankia nodulation in Casuarina glauca (Gherbi et al. 2008). The N-fixing Frankia strains of Casuarinaceae live in a close to obligate association with their hosts and have not been found in the soil outside the native range of the family (Norman et al. 2006). See Subbarao and Rodríguez-Barranco (1995) for microbes associated with Casuarina.
In New Caledonian Gymnostoma, at least, there are root nodules, modified roots, that are formed in association with ECM fungi (Duhoux et al. 2001), however, species like C. glauca may be AM (Duponnois et al. 2003; see also Rose 1980); Tedersoo and Brundrett (2017) suggest that the ECM habit is commonest in Allocasuarina.
Chemistry, Morphology, etc.. Do flavananols occur in this family? The starch grains are distinctive (Czaja 1978). Crystals have been observed in the cuticle (Flores & Moseley 1982). For cork cambium initiation, see de Cordemoy (1923 and references), and for nodal anatomy, with the leaf traces traversing the cortex for the internode before exiting to a leaf, see Balfour and Philipson (1962). There are no intermediates between the cotyledons and scale leaves, and there is a whorl of buds at the cotyledonary node (Hwang & Conran 2000).
The texture of what some have called the outer and inner bracteoles of the staminate flowers is very different; the latter are called the perianth here, however, inflorescence development is clearly very complex (Flores & Moseley 1982). In a floral diagram, Swamy (1948b) illustrated collateral carpels, but he talked about the carpels as if they were superposed (as also in Swamy 1955). The ovules are described as being orthotropous by Johnson and Wilson (1993), but they are drawn as anatropous by Treub (1891), Swamy (1948b) and Flores and Moseley (1982). Although Swamy (1944, 1948b) mentioned quite well developed parietal tissue in the ovule, in the first article a well-developed nucellar cap is illustrated. The nucellus of Casuarina montana (= C. junghuhniana) protrudes broadly between the integuments, so the apex of the nucellus is exposed and there is a sort of nucellar beak; this is because of the great development of the megaspore mother cells in the lower part of the nucellus (Swamy 1948).
See also de Cordemoy (1923), Rogers (1982a), Dilcher et al. (1990) and Johnson and Wilson (1993) for general information; also Hegnauer (1964, 1989: chemistry), Poisson (1874: stem anatomy), Moseley (1948: wood anatomy), Coetzee and Praglowski (1984: pollen) and Sogo et al. (2001: fertilization).
Phylogeny. Steane et al. (2003) provide a phylogeny of the family. Gymnostoma is sister to the rest (see also X.-G. Xiang et al. 2014; M. Sun et al. 2016) and it also has many plesiomorphous features. Both its carpels are fertile (although this feature is likely to be an apomorphy, given the situation in the rest of the order), with 2 ovules/carpel, its stem stomata are not hidden, and perhaps n = 8.
Classification. Although the monophyly of Causarina s.l. has never been in doubt, it has been split into four genera, themselves monophyletic.
[Ticodendraceae + Betulaceae]: sclereid nests in bark, cells with large rhomboidal crystals; mucilage cells +; leaves two-ranked; anther thecae ± separate.
Age. The age of this node is about 302-211 Ma (Forest et al. 2005: huge confidence intervals), around 76.7 Ma (Sauquet et al. 2012), about 143 or 88 Ma (Grimm & Renner 2013), or (80.3-)74.0(-66.9) Ma (X.-G. Xiang et al. 2014).
TICODENDRACEAE Gómez-Laurito & L. D. Gómez P. - Back to Fagales
Buds not perulate?; foliar hypodermal idioblasts +; hairs T-shaped, unicellular, not glandular; lamina margin serrate, stipules encircling the stem; plant (polygamo-)dioecious; staminate flowers: inflorescence erect; P 0; A 8-10+, filaments = or longer than anthers; carpelate flowers: flower single; ?P minute, connate; (staminodes +); G ?tangentially arranged, with deeply lobed loculi; ovules hemitropous, integument 20-30 cells across, parietal tissue ca 6 cells across, nucellar cap 0, ?supra-chalazal tissue; fruit large, drupaceous, stone longitudinally ridged; integument well vascularized, exotestal cells initially radially elongated, all cells ± thick-walled and tanniniferous; endosperm development?; n = 13.
1 [list]/1: Ticodendron incognitum. Central America (map: from Hammel & Burger 1991, fossil locations from Manchester 2011: blue). [Photo - Fruit.]
Evolution: Divergence & Distribution. Ferrignocarpus fruits assignable to Ticodendraceae have been found in Middle Eocene deposits from Oregon and Early Eocene deposits in the London Clay; they are up to ca 50 Ma (Manchester & Renner 2005; Manchester 2011). Chambers and Poinar (2014) report female flowers from Tertiary Dominican amber.
Chemistry, Morphology, etc.. The nodes are trilacunar, judging from the condition in the outer cortex. Lersten and Horner (2008c) describe hypodermal idioblasts (they also occur below the midrib); these sometimes contain druses, and the authors suggest that they may be an apomorphy for the family. Almost all the leaf teeth are vascularized directly by secondary veins, unlike Betulaceae.
The bracteoles of the carpelate flowers have groups of vascularized scales in their axils, suggesting that the carpelate inflorescence has a fundamentally cymose construction. Interestingly, Feuer (1991) did not find much similarity between the pollen of Ticodendron and that of Juglandaceae, Fagaceae, Nothofagaceae, or even Betulaceae. The embryology is poorly known.
For information, see Kubitzki (1993b: general), Carlquist (1991a: wood), Tobe (1991: floral morphology), and Sogo and Tobe (2008: fertilization).
BETULACEAE Gray, nom. cons. - Back to Fagales
Flavones +; stratified phloem +; sieve tube P-protein usu. 0; lamina vernation usu. laterally or vertically conduplicate, margin doubly serrate, colleters +; plant monoecious or dioecious, catkinate, (bracts peltate); staminate flowers: cymule with <3 flowers, bracts 2/cymule; filaments ± divided), anthers longer than connective; pollen starchy; pistillode 0; carpelate flower: inflorescence catkinate; staminodes 0; G [(3)], collateral, septae incomplete, (short style +); ovules (1-4/carpel), collateral (superposed), lower part of integument vascularized; (megaspore mother cell 1); endosperm slight; n = 8, 11, 14; horizontal transfer of rps11 gene; sporophytic incompatibility system present; germination epigeal.
6[list]/145 - 2 groups below. North Temperate, to Andes and Sumatra (map: from Meusel et al. 1965; Hultén 1971). [Photo - Flower.]
Age. Crown-group Betulaceae may be around 131-115 Ma (Forest et al. 2005: large confidence intervals), about 64 Ma (Sauquet et al. 2012), about 63-43 Ma (Grimm & Renner 2013: preferred age, one estimate twice this), (72.5-)64.4(-59.4) Ma (X.-G. Xiang et al. 2014), (88.6-)85.9(-83) Ma (H.-L. Li et al. 2015: Alnus sister to the rest of the family) or (74.3-)70.5(-66.6) Ma (Z. Yang et al. 2019). A crown age of 25 Ma was suggested by Quirk et al. (2012: stem - ?what - 36 My) and (74.9-)69.5(-63.7) Ma by X.-Y. Yang et al. (2018).
The oldest fossils possibly assignable to the family are from 94-83 Ma (see Crepet et al. 2004 and Forest et al. 2005 for references); Bedellia pusilla, the plant involved, was described from east North America (Sims et al. 1999; not included in Larson-Johnson 2015). Normanthus and Endressianthus (see above), from the late Cretaceous of Portugal, may also be close to the root of the Betulaceae clade (Friis et al. 2005, see esp. 2011), but the former is described as having perfect flowers with five perianth members alternating with the stamens and an ovary with parietal placentation (Schönenberger et al. 2001b; Friis et al. 2003a). Both are placed outside crown-group Fagales by Larson-Johnson (2015).
1. Betuloideae Arnott
Plant deciduous; (cluster roots + - Alnus), (N-fixing Frankia +), (ectomycorrhizal); spirally-thickened vessel elements 0, tracheids +; peltate glandular hairs +; (prophyll adaxial - Alnus), (buds naked - some Alnus); (leaves spiral - Alnus); bracts (4/cymule [inc. 2 tertiary bracts] - Alnus); staminate flowers: P 4; pollen grains (4< porate), endexine lamellate; carpelate flowers: (inflorescence cone-like - Alnus), flowers 2-3/cymule; P 0 (2); parietal tissue 1-2 cells across, nucellar cap ca 2 cells across, suprachalazal tissue?; infructescence with woody or scaly bracts separate from fruit, nut small [<3 mm long], ± flattened, samaroid; genome size [1C] 0.2-0.75 pg.
2/95: Betula (60). N. hemisphere, to about 28o S. along the Andes in South America.
Age. The two genera diverged 25-19 Ma (Wikström et al. 2001) or (28-)20, 18(-10) Ma (Bell et al. 2010). Other estimates are older: 109-92 Ma (Forest et al. 2005: large confidence intervals), about 60-38 Ma (Grimm & Renner 2013: preferred age, some estimates almost double), (66.0-)59.6(-46.8) Ma (X.-G. Xiang et al. 2014) or (64.3-)61.1(-58.7) My (X.-Y. Yang et al. 2018) with the crown group ages of the two genera either about half or less than a third to a fifth of this respectively, or (71-)61.8(-49.8) Ma (Z. Yang et al. 2019).
The earliest records of the distinctive infructescences of Alnus are Palaeocene in age (X. Liu et al. 2014). Particularly complete material of Betula leopoldae was collected from deposits ca 52.1 Ma in British Columbia (Crane & Stockey 1987).
2. Coryloideae J. D. Hooker
Plant usu. deciduous; spirally-thickened vessel elements +, tracheids 0; lamina vernation conduplicate-plicate [Corylus]; staminate flowers: individuality ± obscure; bracts usu. 0 (+ - Corylus); P 0; A hairy; carpelate flowers: (inflorescence 1-5-flowered, ± erect - Corylus), usu. 2 flowers/cymule, bracts ± encircling flower; P primordium ± annular; integument 6-11 cells across, parietal tissue 4-8 cells across, nucellar cap 0-2 cells across, (suprachalazal tracheids +); embryo sac with chalazal caecum; pollen tube penetrates the chalazal/lateral pole of the embryo sac; fruit with accrescent leafy bracteoles [from one or two orders of branching]; nuts large to medium, not or little flattened; germination (hypogeal - Corylus).
4/50: Corylus (20). N. Temperate, South East Asia, Central America.
Age. The crown-group age of Coryloideae is estimated to be 87.5-70 Ma (Forest et al. 2005), about 39-22 Ma (Grimm & Renner 2013), (56.4-)54(-50.6) Ma (X.-G. Xiang et al. 2014), (53.9-)36.8(-18.6) Ma (X.-Y. Yang et al. 2018), (48.9-)47.9(-46.9) Ma (Z. Yang et al. 2019) or (78.7-)53.9(-36.2 Ma) (T. Zhao et al. 2019: Ostryopsis and Corylus divergence, sister genera).
Synonymy: Carpinaceae Vest, Corylaceae Mirbel
Evolution: Divergence & Distribution. For numerous Betulaceae around 50 Ma collected from British Columbia, see references in Greenwood et al. (2016). For other clade ages in the family, see X.-Y. Yang et al. (2018), and within Corylus, see T. Zhao et al. (2019).
T. Zhao et al. (2019) discussed diversification and biogeorgraphic relationships within Corylus, a genus that may have originated in southwestern China.
There has been an increase in diversification rate in Betulaceae, perhaps triggered by the acquisition of the deciduous habit, see Bouchenak-Khelladi et al. (2015).
Zhu et al. (2018: Nothofagus outgroup) provide a convenient summary of variation in the family, especially that of floral development, and place it in a phylogenetic context.
Ecology & Physiology. Betula grows with other ECM trees in the boreal forest, and it can be a major component of the biomass in tundra vegetation (Chapin & Körner 1995).
Alnus is common in some neotropical montane forests, A. acuminata dominating in montane cloud forests of the Yungas at 1500-3000 m altitude to about 28o S. (Peay 2016; Wicaksono et al. 2016). Alnus is well known to be a N-fixing plant, hence its use in land remediation. The co-occurrence of N fixation and the ECM habit is rather unusual (but see Fabaceae, Casuarinaceae), and the ECM fungi may also help enhance phosphorus acquisition by the plant (Walker et al. 2013). Cluster roots have been reported from the genus (Skene 1998; Shane & Lambers 2005), although they are rather sporadic in their occurrence and do not seem to be very abundant (Hurd & Schwintzer 1996). Roots of Alnus rubra caused a substantial increase in bedrock weathering, and hence in the access of the plant to the nutrients like phosphorus this would provide (Perakis & Pett-Ridge 2019a); this increase was perhaps caused by nitric acid, itself converted from excess N fixed by Frankia by soil microbes. Lambers et al. (2019, but c.f. Perakis & Pett-Ridge 2019b) think carboxylate exudation by cluster roots may help in phosphorus acquisition here (see also Lambers et al. 2012b).
Pollination Biology & Seed Dispersal. Heterodichogamy is reported from Corylus (Renner 2001 for references). In Corylus avellana in particular there may be three to five months between pollination and fertilization. Ovules start to develop about half way through this period and the developing nuts are already 7-10 mm across at the time of fertilization. If pollination does not occur, the stigma may remain receptive for up to three months (Germain 1994). See also Benson et al. (1906), for pollination, etc., of Carpinus, Nawaschin (1899) for that of Corylus, and Dahl and Fredrikson (1996), fertilization of Betula, for more information.
Fruits of Carpinus develop a vortex at the leading edge of the rotating wing that generates lift, so facilitating wind dispersal (Lentink et al. 2009).
Plant-Animal Interactions. Leaf-mining larvae of Eriocraniidae, probably the subbasal clade in the lepidopteran Angiospermivora, eat Betulaceae (and Fagaceae: Regier et al. 2015 and references).
Bacterial/Fungal Associations. Põlme et al. (2013) reported quite an assemblage of ECM fungi, even if compared with other ECM plants there are not that many species, however, they are unrelated and are rather species-specific (Bruns et al. 2002; Walker et al. 2013; Wicaksono et al. 2017). This may be connected with the tendency of Alnus to be a pioneer, plant-fungus specificity tending to be higher in such situations (Bruns et al. 2002). Both AM and ECM associations have been recorded here (e.g. Rose 1980), and there have been reports that Alnus may lack ECM (Michelsen et al. 1998). 5-15% of fixed 15N2 moved from Alnus glutinosa to Pinus contorta via a common ECM associate (Ekblad & Huss-Danell 1995), although the ecological significance of this is unclear.
Chemistry, Morphology, etc.. Staminate flowers in Coryloideae are sometimes reported as being single (e.g. Mabberley 1997), however, as Abbe (1935) noted, there are usually three together. The staminate "flower" of Ostrya, with some 15 pairs of half stamens, is apparently pseudanthial in nature, being derived from three flowers (Abbe 1935, 1974; Macdonald in Sattler 1973: see also Nothofagaceae). Betula has three carpelate flowers per bract. In staminate flowers of Corylus the perianth is reduced to a ridge, and pollen of C. avellana has spongy endexine at the pore (Weber & Ulrich 2010). The orientation of stamens or carpels in the flower may change during development in Betula and other taxa (Lin et al. 2010; Zhe et al. 2018), while Endress (2008c) discussed the structural lability of carpelate flowers of Carpinus betulus. The ovary of Corylus is not always obviously inferior.
See Crane (1989) and Kubitzki (1993b), both general, Ashburner and McAllister (2013: Betula), Endress (1967: general, comparison with Hamamelidaceae, Corylopsis is the link), Hegnauer (1964, 1989: chemistry), Horne (1914), Heller (1935) and Abbe (1935), all flowers, inflorescences, Z.-Y. Zhang et al. (1994: embryology of Carpinus), and Manchester and Chen (1998: fossils).
Phylogeny. R.-Q. Li et al. (2004) suggested that Betuloideae were paraphyletic, with Alnus and Betula being successively sister to the rest of the family (see also H.-L. Li et al. 2015, 2016; M. Sun et al. 2016; Z.-D. Chen et al. 2016: support very weak). However, Forest et al. (2005), analysing variation in ITS and the 5S spacer, recovered the two subfamilies above as monophyletic (see also Grimm & Renner 2013; X.-G. Xiang et al. 2014; Ma et al. 2015: phylotranscriptomic analyses; X.-Y. Yang et al. 2018; Z. Yang et al. 2019). See also Z.-D. Chen et al. (1999) for the phylogeny and evolution of the family.
The ITS phylogeny of Betula provided by N. Wang et al. (2016) suggests that there has been hybridization, even between species now placed in separate subgenera. Corylus is sister to other Coryloideae in both molecular (e.g. Grimm & Renner 2013) and morphological (Zhe et al. 2018) analyses. The monophyly of Ostrya and Carpinus is unclear, the latter genus perhaps being paraphyletic (see Yoo & Wen 2002, 2007, 2008; Xiang et al. 2014). In a plastome analysis of X.-Y. Yang et al. (2018) the two were monophyletic, but in their ITS tree Carpinus was paraphyletic. Ostryopsis was sister to [Ostrya + Carpinus] in another complete plastome analyses, but sister to Corylus in intergenic spacer region analyses (Z. Yang et al. 2019), although it was in the former position in all analyses in X.-Y. Yang et al. (2018). There has been extensive chloroplast capture in Corylus, analyses of chloroplast and nuclear genomes giving quite different topologies (T. Zhao et al. 2019).
Classification. The two subfamilies have sometimes been recognised as families, as by Brummitt (1992).
For a checklist and bibliography, see Govaerts and Frodin (1998: as Corylaceae and Betulaceae). For an infrageneric classification of Betula, see Ashburner and McAllister (2013), but c.f. N. Wang et al. (2016) and for that of Corylus, see T. Zhao et al. (2019: four sections).