EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, thalloid, with single-celled apical meristem, showing gravitropism; rhizoids +, unicellular; acquisition of phenylalanine lysase [PAL], flavonoids [absorbtion of UV radiation], phenylpropanoid metabolism [lignans, also lignins], xyloglucans +; plant poikilohydrous [protoplasm dessication tolerant], ectohydrous; cuticle +; cell wall also with (1->3),(1->4)-ß-D-MLGs [Mixed-Linkage Glucans]; chloroplasts per cell, lacking pyrenoids; glycolate metabolism in leaf peroxisomes [glyoxysomes]; centrioles in vegetative cells 0, metaphase spindle anastral, predictive preprophase band of microtubules, phragmoplast + [cell wall deposition spreading from around the spindle fibres], plasmodesmata +; antheridia and archegonia jacketed, stalked; spermatogenous cells monoplastidic; blepharoplast, bicentriole pair develops de novo in spermatogenous cell, associated with basal bodies of cilia [= flagellum], multilayered structure [4 layers: L1, L4, tubules; L2, L3, short vertical lamellae] + 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; oogamy; sporophyte dependent on gametophyte, embryo initially surrounded by haploid gametophytic tissue, plane of first division horizontal [with respect to long axis of archegonium/embryo sac], suspensor/foot +, cell walls with nacreous thickenings; sporophyte multicellular, with at least transient apical cell [?level], sporangium +, single, dehiscence longitudinal; meiosis sporic, monoplastidic, microtubule organizing centre associated with plastid, cytokinesis simultaneous, preceding nuclear division, sporocytes 4-lobed, with a quadripolar microtubule system; spores in tetrads, sporopollenin in the spore wall, wall with several trilamellar layers [white-line centred layers, i.e. walls multilamellate]; nuclear genome size <1.4 pg, LEAFY gene present, ethylene involved in cell elongation; chloroplast genome with close association between trnLUAA and trnFGAA genes.
Many of the bolded characters in the characterization above are apomorphies of subsets 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.
Abscisic acid, ?D-methionine +; sporangium with seta developing from basal meristem [between epibasal and hypobasal cells], sporangial columella + [developing from endothecial cells]; stomata +, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; underlying similarities in the development of conducting tissue and in rhizoids/root hairs; spores trilete; polar transport of auxins and class 1 KNOX genes expressed in the sporangium alone; shoot meristem patterning gene families expressed; MIKC, MI*K*C* and class 1 and 2 KNOX genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns.
[Anthocerophyta + Polysporangiophyta]: archegonia embedded/sunken in the gametophyte; sporophyte long-lived, chlorophyllous; sporophyte-gametophyte junction interdigitate, sporophyte cells showing rhizoid-like behaviour.
Sporophyte branched, branching apical, dichotomous; sporangia several, each opening independently; spore walls not multilamellate [?here].
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Photosynthetic red light response; plant homoiohydrous [water content of protoplasm relatively stable]; control of leaf hydration passive; (condensed or nonhydrolyzable tannins/proanthocyanidins +); sporophyte soon independent, dominant, with basipetal polar auxin transport; vascular tissue +, sieve cells + [nucleus degenerating], tracheids +, in both protoxylem and metaxylem, plant endohydrous; endodermis +; stem with an apical cell; branching dichotomous; leaves spirally arranged, blades with mean venation density 1.8 mm/mm2 [to 5 mm/mm2]; sporangia adaxial on the sporophyll, derived from periclinal divisions of several epidermal cells, wall multilayered [eusporangium]; columella 0; tapetum glandular; gametophytes exosporic, green, photosynthetic; basal body 350-550 nm long, stellate array in transition region initially joining microtubule triplets; placenta with single layer of transfer cells in both sporophytic and gametophytic generations, root lateral with respect to the longitudinal axis of the embryo [plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Sporophyte branching ± indeterminate; root apex multicellular, root cap +, lateral roots +, endogenous; endomycorrhizal associations + [with Glomeromycota]; tracheids with scalariform-bordered pits; leaves with apical/marginal growth, venation development basipetal, growth determinate; sporangia borne in pairs and grouped in terminal trusses, dehiscence longitudinal, a single slit; cells polyplastidic, microtubule organizing centres not associated with plastids, diffuse, perinuclear; blepharoplasts +, paired, with electron-dense material, centrioles on periphery, male gametes multiciliate; chloroplast long single copy ca 30kb inversion [from psbM to ycf2]; LITTLE ZIPPER proteins.
Sporophyte woody; lateral root origin from the pericycle; branching lateral, meristems axillary; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
EXTANT SEED PLANTS / SPERMATOPHYTA
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins derived from (some) sinapyl and particularly coniferyl alcohols [hence with p-hydroxyphenyl and guaiacyl lignin units, so no Maüle reaction]; root stele with xylem and phloem originating on alternate radii, cork cambium deep seated; shoot apical meristem interface specific plasmodesmatal network; stem with vascular cylinder around central pith [eustele], phloem abaxial [ectophloic], endodermis 0, xylem endarch [development centrifugal]; 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; leaves with single trace from vascular sympodium [nodes 1:1]; stomatal pore with active opening in response to leaf hydration, control by abscisic acid, metabolic regulation of water use efficiency, etc.; buds axillary (not associated with all leaves), exogenous; prophylls two, lateral; leaves with petiole and lamina, development basipetal, blade simple; plant heterosporous, sporangia borne on sporophylls, sporophylls spiral; microsporophylls aggregated in indeterminate cones/strobili; grains monosulcate, aperture in ana- position [distal], exine and intine homogeneous; ovules unitegmic, parietal tissue 2+ cells across, megaspore tetrad linear, functional megaspore single, chalazal, lacking sporopollenin, megasporangium indehiscent; pollen grains land on ovule; gametophytes dependent on sporophyte; apical cell 0, male gametophyte development initially endosporic, tube developing from distal end of grain, gametes two, developing after pollination, with cell walls; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; embryo cellular ab initio, endoscopic, plane of first cleavage of zygote transverse, suspensor +, short-minute, embryonic axis straight [shoot and root at opposite ends; plant allorhizic], cotyledons 2; plastid transmission maternal; ycf2 gene in inverted repeat, whole nuclear genome duplication [zeta duplication], two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], nrDNA with 5.8S and 5S rDNA in separate clusters; mitochondrial nad1 intron 2 and coxIIi3 intron and trans-spliced introns present.
ANGIOSPERMAE / MAGNOLIOPHYTA
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], S [syringyl] lignin units common [positive Maüle reaction - syringyl:guaiacyl ratio more than 2-2.5:1], and hemicelluloses as xyloglucans; root apical meristem intermediate-open; root vascular tissue oligarch [di- to pentarch], lateral roots arise opposite or immediately to the side of [when diarch] xylem poles; origin of epidermis with no clear pattern [probably 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; reaction wood ?, associated gelatinous fibres [g-fibres] with innermost layer of secondary cell wall rich in cellulose and poor in lignin; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, wood parenchyma +; sieve tubes enucleate, sieve plate with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, cytoplasm not occluding pores of sieve plate, companion cell and sieve tube from same mother cell; sugar transport in phloem passive; nodes 1:?; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule, reduction in stomatal conductance to increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, overall growth ± diffuse, venation hierarchical-reticulate, secondary veins pinnate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic; protogynous; parts spiral [esp. the A], free, numbers unstable, development in general centripetal; P +, members 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], sporangium pairs dehiscing longitudinally by a common slit, ± embedded in the filament, walls with at least outer secondary parietal cells dividing, endothecium +, endothecial cells elongated at right angles to long axis of anther; (tapetum glandular), cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine lamellate only in the apertural regions, thin, compact; nectary 0; carpels present, superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus at most short [shorter than ovary], hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry [not secretory]; 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 [crassinucellate], nucellar cap?; megasporocyte single, hypodermal, functional megaspore, chalazal, lacking cuticle; female gametophyte four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; supra-stylar extra-gynoecial compitum +; ovule not increasing in size between pollination and fertilization; pollen grains land on stigma, bicellular at dispersal, mature male gametophyte tricellular, germinating in less than 3 hours, pollen tube elongated, unbranched, growing between cells, growth rate (20-)80-20,000 µm/hour, 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 gametes lacking cell walls, cilia 0, siphonogamy; double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; mature seed much larger than ovule when fertilized, small , dry [no sarcotesta], exotestal; endosperm diploid, cellular, heteropolar [micropylar and chalazal domains develop differently, 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; dark reversal Pfr → Pr; Arabidopsis-type telomeres [(TTTAGGG)n]; nuclear genome size <1.4 pg [1 pg = 109 base pairs], whole nuclear genome duplication [epsilon duplication]; protoplasm dessication tolerant [plant poikilohydric]; 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, paleo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and three copies of the PHY gene, [PHYB [PHYA + PHYC]].
[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]]]]: vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood +; tectum reticulate; anther wall with outer secondary parietal cell layer dividing; carpels plicate; 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 [possible position]; pollen tube growth intra-gynoecial; embryo sac bipolar, 8 nucleate, antipodal cells persisting; endosperm triploid.
[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (extra-floral nectaries +); (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.
EUDICOTS: (Myricetin, delphinidin +), 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 few, (polyandry widespread, initial primordia 5, 10, or ring, ± centrifugal), 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]; seed coat?
[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]: ?
CORE EUDICOTS / GUNNERIDAE: (ellagic and gallic acids +); leaf margins serrate; compitum + [one place]; micropyle?; whole nuclear genome duplication [palaeohexaploidy, gamma triplication], 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 = calyx + corolla, the calyx enclosing the flower in bud, sepals with three or more traces, petals with a single trace; stamens = 2x K/C, in two whorls, internal/adaxial to the corolla whorl, alternating, (numerous, but then usually fasciculate and/or centrifugal); pollen tricolporate; G , G  also common, when [G 2], carpels superposed, compitum +, placentation axile, style +, stigma not decurrent; endosperm nuclear; fruit dry, dehiscent, loculicidal [when a capsule]; RNase-based gametophytic incompatibility system present; floral nectaries with CRABSCLAW expression; (monosymmetric flowers with adaxial/dorsal CYC expression).
[DILLENIALES [SAXIFRAGALES [VITALES + ROSIDS s. str.]]]: stipules + [usually apparently inserted on the stem].
[SAXIFRAGALES [VITALES + ROSIDS]] / ROSANAE Takhtajan / SUPERROSIDAE: ??
[VITALES + ROSIDS] / ROSIDAE: anthers articulated [± dorsifixed, transition to filament narrow, connective thin].
ROSIDS: (mucilage cells with thickened inner periclinal walls and distinct cytoplasm); embryo long; genome duplication; chloroplast infA gene defunct, mitochondrial coxII.i3 intron 0.
ROSID II / MALVIDAE / [[GERANIALES + MYRTALES] [CROSSOSOMATALES [PICRAMNIALES [SAPINDALES [HUERTEALES [MALVALES + BRASSICALES]]]]]]: ?
[CROSSOSOMATALES [PICRAMNIALES [SAPINDALES [HUERTEALES [MALVALES + BRASSICALES]]]]]: ?
[PICRAMNIALES [SAPINDALES [HUERTEALES [MALVALES + BRASSICALES]]]]: ovules 2/carpel, apical.
[SAPINDALES [HUERTEALES [MALVALES + BRASSICALES]]]: flavonols +; vessel elements with simple perforation plates; (cambium storied); petiole bundle(s) annular; style +; inner integument thicker than outer; endosperm scanty.
[HUERTEALES [MALVALES + BRASSICALES]]: ?
Age. The age of this node was estimated to be (104-)96, 86(-75) m.y. (Bell et al. 2010).
Phylogeny. For discussion see the Sapindales page.
HUERTEALES Doweld Main Tree.
Vessel elements with scalariform perforation plates; mucilage cells +; lamina margins toothed, stipules cauline; inflorescence cymose; flowers "small" [<8 mm across], hypanthium +, short, A = C, opposite K; G , ovary unilocular; fruit a berry; exotegmen rather massive, of more or less strongly laterally-compressed fibres; endosperm +, embryo at most medium. - 4 families, 6 genera, 24 species.
Note: Possible apomorphies are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned is unclear. This is partly because many characters show considerable homoplasy, in addition, basic information for all too many 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 is the not-so-trivial issue of how ancestral states are reconstructed (see above).
Evolution. Divergence & Distribution. For some comments on the biogeography of the groups, see Christenhusz and Chase (2013).
Chemistry, Morphology, etc. Overall, the flowers of Huerteales seem to be rather similar, although there is variation in androecial position in particular. The mechanical (lignified) layer of the seed may differ in its origin within the order, but I have tentatively suggested that exotegmic seeds are a synapomorphy for the clade, however, developmental studies of seeds of taxa like Gerrardina and Petenaea are much needed.
Worberg et al. (2009) summarize what is known about this group, and information in their summary is slightly emended below; see also Yang et al. (2009) for chromosome numbers.
The morphology, anatomy, and secondary chemistry of the whole group are badly in need of detailed investigation.
Phylogeny. For the association of the Tapisciaceae and Dipentodontaceae, see Peng et al. (2003), also James Horn (pers. comm.). Perrottetia was previously in Celastraceae, if only rather uneasily so; molecular data suggested that it was to be placed near Tapiscia (M. Simmons, in Matthews & Endress 2005b), a placement with which its morphology is in general agreement. Gerrardina eylesiana shows a possibly superficial but still striking similarity to Perrottetia in particular, and there may be a similarity in seed coat anatomy between the two, yet they do not appear to be sister taxa (Worberg et al. 2009). Petenaea has been found to be rather weakly (bootstrap) associated with Gerrardina, and in general bootstrap values for relationships are low, even if posterior probabilities are higher (Christenhusz et al. 2010). Relationships within the order seem to be [[Gerrardinaceae + Petenaeaceae] [Tapisciaceae + Dipentodontaceae]], although Dipentodon is sister to Tapisciaceae in some analyses (Worberg et al. 2009).
Classification. Like Crossosomatales, Huerteales have accumulated several small families; when the clade is better known, rationalization (= reduction in number) may be in order - we hardly know enough so say whether or not the families are similar other than in gross phenetic terms, and none is of any size.
Includes Dipentodontaceae, Gerrardinaceae, Petenaeaceae, Tapisciaceae.
Synonymy: Dipentodontales C. Y. Wu et al. - Huerteanae Thorne & Reveal
[Gerrardinaceae + Petenaeaceae]: leaves spiral, lamina margins serrate; nectary inside A; placentation apical.
GERRARDINACEAE M. H. Alford Back to Main Tree
Vessel elements with scalariform perforation plates; petiole bundle arcuate, or three in an arc; mucilage cells in epidermis; lamina with vein proceeding to glandular tooth and with a branch to the vein above; C clawed, thin, small; A opposite C; nectary cupular; stigma?; ovules?; seed with a fleshy outer layer, lignified laterally-compressed cells inside; endosperm ?type, embryo minute; n = ?
1[list]/2. Eastern and southern Africa (map: data from Trop. Afr. Fl. Pl. Ecol. Distr. 1. 2003; GBIF, vii.2009).
Chemistry, Morphology, etc. Gerrardina foliosa appears to have clawed petals and three sepals larger than the others (ToL, vii.2009).
See Alford (2006) for what little is known about the family; the description of the venation is modified from that source. Christenhusz et al. (2010) describe the wood anatomy of young stems. In addition, see G. eylesiana: stem anatomy, J. D. & E. G. Chapman 9242; leaf anatomy, Brass 16641; seed anatomy, Iversen et al. 85748; G. foliosa: stem and seed anatomy, Strey 11052; leaf anatomy, Hilliard & Burtt 6751.
Previous Relationships. Gerrardina has previously been included in Flacourtiaceae.
PETENAEACEAE Christenhusz, M. F. Fay & M. W. Chase Back to Main Tree
Vessels in radial multiples; lamina venation palmate, stipules +; P +, uniseriate, valvate, with adaxial moniliform hairs and basal glands; A 8-12; G , placentae pendent, style long; ovules many; berry lobed, with a persistent style; n = ?
1/1: Petenaea cordata. Central America (map: from Christenhusz et al. 2010).
Chemistry, Morphology, etc. For the wood anatomy of Petenaea, see also Kukachka (1962). The genus is described as having minute stipules (Bayer 2002). For some general information, see Christenhusz et al. (2010).
Previous Relationships. Petenaea has previously been linked with Tiliaceae and Elaeaocarpaceae (Mabberley 2009), Bayer et al. (1999, but sampling) had suggested on molecular data that it might be associated with Malvales, being tentatively associated with Muntingiaceae (see also A.P.G. 2003).
[Tapisciaceae + Dipentodontaceae]: wood parenchyma 0.
TAPISCIACEAE Takhtajan Back to Main Tree
Wood fluorescing; fibres with simple pits; nodes also 5:5; petiole bundle annular, fibrous sheath 0; stomata paracytic; leaves spiral, odd-pinnately compound or trifoliolate, glands or stipels at articulations; K connate or not; (anthers extrorse, inflexed - Huertea); pollen colpate; nectary not vascularized (0); G septate or not, style hollow, apically branched or styles ± separate, stigma?; ovule 1/carpel, basal, apotropous, outer integument 2-3 cells across, inner integument 2-3 cells across, parietal tissue 4-6 cells across, hypostase +; (fruit a drupe); testa thin-walled, (mesotesta sclerotic), chalaza/hypostase ballooning into endosperm; endosperm ?type, embryo medium to small, coyledons flat; n = 13, 15.
2[list]/5. China (Tapiscia sinensis), West Indies and N.W. South America (map: from Ying et al. 1993; GBIF and TROPICOS vii.2009; fossils [blue] from Manchester 1988). [Photo - Fruit]
Evolution. Divergence & Distribution. The distinctive fruits of Tapiscia are known from the Eocene onwards in Europe, and somewhat later in North America (Manchester 1988; Manchester et al. 2009 and references).
Chemistry, Morphology, etc. Dickison (1987b) noted that small accessory traces from the central bundle also proceeded into the leaves.
The pollen of Tapisciaceae is smaller than that of Staphyleaceae, being only some 13-18 µm long (Jin & Wei 2002). There is quite a prominent nectariferous disc in Huertea, but it is not vascularized (Dickison 1986a; Danilova 1996). In Tapiscia sinensis, at least, the fruit takes about eighteen months to develop, the receptacle also becoming inflated and suberised (Liu et al. 2008; Teng & Liu 2009). In the ripe fruit the seed is born in the middle of the loculus, perhaps partly due to the strong post-fertilization development of the hypostase (Liu & Ni 2013).
See also Corner (1976: seed anatomy), Carlquist and Hoekman (1985: wood anatomy), Dickison (1987a: pollen morphology) and Wei et al. (2002: pollen of Tapiscia), and for general information, see Kubitzki (2002d).
Previous Relationships. The two genera that make up the family were long included in Staphyleaceae (but see Corner 1976 for differences in seed coat and Dickison 1987b for a table of differences separating them from the rest of Staphyleaceae) and placed in Sapindales by Cronquist (1981), while a segregated Tapisciaceae were still included in Sapindales by Takhtajan (1997).
Synonymy: Huerteaceae Doweld
DIPENTODONTACEAE Merrill, nom. cons. Back to Main Tree
Trees; leaves two-ranked, secondary veins pinnate, stipules +; K and C similar, K ± valvate; ovules 2/carpel, basal, erect, micropyle endostomal [Perrottetia]; K + C persistent in fruit; endosperm ?type.
2/[list]16. Southeast Asia to Malesia, Mexico to Peru.
1. Dipentodon Dunn
Petiole bundle arcuate; ?stomata; hairs uniseriate; stipules lobed; inflorescence umbellate; flowers 5(-7)-merous, hypanthium spreading; K valvate, basally connate, C valvate; nectaries opposite petals [?staminodia]; G , placentation axile basally, ovules borne on top of placenta, with a free-central prolongation, stigma punctate; ovule ?morphology; fruit laterally compressed, ?septicidally dehiscent from the base upwards, funicle ?much enlarged; seed single; coat with obliquely-lying lignified ribbon cells, collapsed polygonal cells underneath; embryo ?very short; n = 17.
1/1: Dipentodon sinicus. S. China and adjacent Burma, India and Vietnam (map: from Yuan et al. 2008).
2. Perrottetia Kunth
(Vessel elements simple); paratracheal parenchyma +; sclereids +; petiole bundle depressed annular with an adaxial inverted bundle and wing bundles; stomata anomocytic (anisocytic); (leaves spiral); inflorescence thyrsoid, ultimate units ± cymose; (flowers 4-8-merous); ovary septate, style short; ovules epi-apotropous; testa thin-walled, ± fleshy, inner tangential walls of endotesta with rod-like structures, exotegmen ridged; embryo medium; n = 10.
1/ca 15. China to Malesia and N.E. Australia, Hawaii, Mexico to Bolivia (map: from Ding Hou 1962; Thorne 1972; FoC vol. 11. 2008: New World rather approximate).
Chemistry, Morphology, etc. The flowers of Perrottetia may be imperfect; Ding Hou (1962) described and illustrated the nectary as being disc-like and entire (c.f. Bachelier & Merran 2014). It has idioblasts in the sepals with thickened inner tangential walls, and the seeds lack an aril (Corner 1976; c.f. Ding Hou 1962; Yang et al. 2009).
Mabberley (1997) described the leaves of Dipentodon as being spiral. In the two flowers that I examined I could find only a single well-developed ovule in each.
For general information on Perrottetia, see Ding Hou (1962), for floral morphology, etc., see Matthews and Endress (2005b: also mucilage cells!), for mostly stomatal morphology, see den Hartog and Baas (1978), for vegetative anatomy, see P. sessiliflora - Cogollo et al. 7294. For general information on Dipentodon, see Merrill (1941), for pollen, see Lobreau-Callen (1982), and for floral morphology see Liu and Cheng (1991: comparison with putatively related taxa) and Bachelier and Matthews (2014).
Previous relationships. Dipentodontaceae were included in Santalales by Cronquist (1981) because of apparent similarities in gynoecial structure, but the toothed lamina margin and large, lobed stipules suggested that this was incorrect. They were placed by Takhtajan (1997) in his Violales (= Malpighiales), while Wu et al. (2002, 2003) recognised a Dipentodontales C. Y. Wu et al. in Dilleniidae, where it was placed between Passiflorales (which included Caricaceae) and Violales (Cucurbitales were next).