EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, initially ±globular, not motile, branched; showing gravitropism; acquisition of phenylalanine lysase* [PAL], flavonoid synthesis*, microbial terpene synthase-like genes +, triterpenoids produced by CYP716 enzymes, 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; glycolate metabolism in leaf peroxisomes [glyoxysomes]; 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; 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 [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]; nuclear genome size [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 gene moved to nucleus; mitochondrial trnS(gcu) and trnN(guu) 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, L- and D-methionine distinguished metabolically; pro- and metaphase spindles acentric; class 1 KNOX genes expressed in sporangium alone; sporangium wall 4≤ cells across [≡ eusporangium], tapetum +, secreting sporopollenin, which obscures outer white-line centred lamellae, columella +, developing from endothecial cells; stomata +, on sporangium, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; underlying similarities in the development of conducting tissue and of rhizoids/root hairs; spores trilete; shoot meristem patterning gene families expressed; MIKC, MI*K*C* genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns, mitochondrial trnS(gcu) and trnN(guu) genes 0.
[Anthocerophyta + Polysporangiophyta]: gametophyte leafless; archegonia embedded/sunken [only neck protruding]; sporophyte long-lived, chlorophyllous; cell walls with xylans.
Sporophyte well developed, branched, branching apical, dichotomous, potentially indeterminate; hydroids +; stomata on stem; sporangia several, terminal; spore walls not multilamellate [?here].
Vascular tissue + [tracheids, walls with bars of secondary thickening]; stomata numerous, involved in gas exchange.
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Sporophyte with 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]; sporophyte with polar auxin transport, PIN [auxin efflux facilitator] involved; (condensed or nonhydrolyzable tannins/proanthocyanidins +); xyloglucans with side chains uncharged [?level], in secondary walls of vascular and mechanical tissue; lignins +; roots +, 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 +; leaves/sporophylls spirally arranged, blades with mean venation density ca 1.8 mm/mm2 [to 5 mm/mm2], all epidermal cells with chloroplasts; sporangia adaxial, columella 0; tapetum glandular; ?position of transfer cells; MTOCs not associated with plastids, basal body 350-550 nm long, stellate array in transition region initially joining microtubule triplets; 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; 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 lateral, meristems axillary; lateral root origin from the pericycle; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
Growth of plant bipolar [roots with positive geotropic response]; 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].
EXTANT SEED PLANTS / SPERMATOPHYTA
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]; root stele diarch to pentarch, xylem and phloem originating on alternating radii, cork cambium deep seated; 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.; 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; female gametophyte initially syncytial, walls then surrounding individual nuclei; embryo cellular ab initio, suspensor short-minute, embryonic axis straight [shoot and root at opposite ends; plant 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], two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], 5.8S and 5S rDNA in separate clusters.
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; 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; 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, 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 brachyparacytic [ends of subsidiary cells level with ends of pore], 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 +, ?insertion, 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], 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 lamellate only in the apertural regions, thin, compact, intine in apertural areas thick, pollenkitt +; nectary 0; carpels present, superior, free, several, 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 [no photosynthesis], four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; 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 towards the ovule, 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, ciliae 0, siphonogamy; double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; mature seed much larger than fertilized ovule, small [<5 mm long], dry [no sarcotesta], exotestal; endosperm +, 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 size [1C] <1.4 pg [mean 1C = 18.1 pg, 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.
Evolution. Possible apomorphies for flowering plants are in bold. The actual level at which many characters, particularly the more cryptic ones, should be assigned is unclear. This is because some taxa basal to the [magnoliid + monocot + eudicot] group have been surprisingly little studied, there is considerable homoplasy as well as variation within and between families of the ANITA grade in particular for several of these characters, and also because details of relationships among gymnosperms will affect the level at which some of these characters are pegged. For example, if reticulate-perforate pollen is optimized to the next node on the tree (see Friis et al. 2009b for a discussion), it effectively makes the pollen morphology of the common ancestor of all angiosperms ambiguous... Ther are other features such as a nucellus only one (Nymphaeales) to three cells thick above the embryo sac and a stylar canal lacking an epidermal layer that appear to be plesiomorphous for basal grade angiosperms (Williams 2009), however, where on the tree a thicker nucellus and a stylar epidermal layer are acquired has not been indicated.
[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. Back to Main Tree
Age. Wikström et al. (2001) estimated that this node was (179-)171, 153(-145) m.y. old, in line with other early estimates (Magallón 2009); Soltis et al. (2008: a variety of estimates) give an age of 180-132 m.y. ago. Magallón and Castillo (2009) offer an age of ca 229 m.y. for relaxed and 127 m.y. for constrained penalized likelihood datings, while Moore et al. (2010: 95% HPD) suggest an age of (162-)155(-145) m.y., Clarke et al. (2011: 95% credibility intervals) ages of (231-)197(-169) m.y., towards the upper end of the suggestions then, N. Zhang et al. (2012; see also Xue et al. 2012) ages of (211-)179(-158) m.y., and Magallón et al. (2013) an age of around 183.4 m.y. ago. Ages around ca 139 m.y.a. (Magallón et al. 2015) and 184.5-173 m.y.a. are suggested in Naumann et al. (2013) and, the other extreme, (266, 233-)227, 195(-173) m.y. by Zeng et al. (2014) and ca 255 m.y.a. by Z. Wu et al. (2014).
A fossil-based estimate for the age of this node is ca 113 m.y. (Crepet et al. 2004).
Evolution: Divergence & Distribution. For discussion as to where characters of pollen morphology and development are to be placed on the tree, see Taylor and Osborn (2006) and also Friis et al. (2009b); it partly depends on how the characters are defined and partly on the recent discovery of fossil Nymphaeales that do not have the pollen characteristics of extant members of the clade. For vessel evolution in angiosperms, including that in Nymphaeales, see the Amorellales page.
Chemistry, Morphology, etc. Cabombaceae and Nymphaeaceae do have vessels of a sort (Carlquist & Schneider 2009; Schneider & Carlquist 2009).
For cell lineages in the embryo sac see Huang and Russel (1992) and Friedman (2006); identification of the pattern described above apparently goes back to Porsch (1907), although it has been observed for relatively few plants. For embryo sac evolution, see Friedman and Ryerson (2009). For the possibility of a genome duplication at about this position, see Cui et al. (2006) and dePamphilis et al. (2009).
Phylogeny. For discussion of the relationships of Nymphaeales, see the Magnoliophyta node.
NYMPHAEALES Dumortier Main Tree.
Aquatic herbs, plant rhizomatous; starch grains compound; primary root soon aborts; root apex with secondary dermatogen, etc., epidermis derived from outer layer of cortex [?Hydatellaceae]; trichoblasts in vertical files, proximal cell smaller; diaphragms in root aerenchyma; mycorrhizae 0; primary stem with ± scattered vascular bundles; protoxylem lacunae +; vascular cambium 0; nodes?; articulated laticifers +; vascular bundles lacking associated sclerenchyma; aerenchyma common; 4-celled uniseriate secretory trichomes with a large terminal cell [hydropoten]; stomata anomocytic; ?lamina margins, leaf base broad; bracts 0; pollen boat-shaped, tectum continuous, infratectal space large, columellae conspicuous; ovule with semi-annular [hood-shaped] outer integument; first division of endosperm transverse, chalazal cell undivided; P persistent; fruit maturation underwater; operculum +, endotegmic [?all], hilum outside operculum; seed coat exotestal, exotestal cells low, thin-walled; endosperm scanty, develops in micropylar half, chalazal haustorium +, single-celled, perisperm +, starchy, precocious, cells ± multinucleate, embryo broad, cotyledons connate; germination hypogeal; intergenic inversion in chloroplast inverted repeat. - 3 families, 6 genera, 74 species.
Age. The age of crown-group Nymphaeales is around 125 m.y. (Magallón et al. (2015), (133.2-)126.7(-120.6) m.y.a. (Iles et al. 2014), as little as (176.6-)97.7(-42.8) m.y.a. (Zhou et al. 2014), or as much as ca 164 (Z. Wu et al. 2014), ca 188 m.y. (Tank et al. 2015) or ca 209 m.y. (Foster et al. 2016a: q.v. for details).
The curious fossil Archaefructus, probably an aquatic plant and about 124 m.y. old, has been linked with Hydatellaceae in morphological analyses (Doyle & Endress 2007, 2010; Doyle 2008b). Although they have very little in common in terms of overall appearance, Archaefructus may be another early aquatic angiosperm with very unconventional floral morphology. Hydatellaceae may be represented in the pollen record from the Isle of Wight in rocks of some 130 m.y. of age (Hoffmann & Zetter 2010).
Numerous other fossils have been identified as members of Nymphaeales; these are discussed below under Cabombaceae and Nymphaeaceae.
Note: Boldface denotes possible apomorphies, (....) denotes a feature common in the clade, exact status uncertain, [....] includes explanatory material. Note that the particular 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).
Evolution: Divergence & Distribution. Cretaceous fossils assignable to Nymphaeaceae are quite common, and it has been suggested that Nymphaeales were "the first globally diverse clade" (Borsch " Soltis 2008: p. 1051; see also Sender et al. 2010). However, looking only at extant taxa, their diversity is slight.
Nymphaeales are a highly derived aquatic clade, so it is unclear to what extent Cabomba or any other member of the order can serve as a model for understanding early angiosperm evolution (c.f. Vialette-Guiraud et al. 2011).
Saarela et al. (2007) suggest a few additional possible synapomorphies for Nymphaeales, and Zeng et al. (2014) thought that having protoxylem lacunae and vascular bundles lacking associated sclerenchyma might be apomorphies. For the development of root hairs, see e.g. Clowes (2000) and Sokoloff et al. (2008a), Borsch et al. (2007) discuss the evolution of a number of floral characters within the order, M. L. Taylor et al. (2015) outline palynological variation in the context of the phylogeny of the order, and Endress and Doyle (2015: floral morphology) also suggest apomorphies. Understanding where some of these should be placed on the tree is complicated by the highly autapomorphic nature of Hydatella and lingering uncertainty over the position of Nymphaeales.
As might be expected, endomycorrhizae are at most uncommon here (e.g. de Marins et al. 2009).
Chemistry, Morphology, etc. Hydrolysable tannins in this group (e.g. in Nuphar) are different to those found elsewhere (Gottlieb et al. 1993; Ishimatsu et al. 1989) - although of course Hydatellaceae are here, as in many other features, very poorly known. Although there are minute perforations in the end walls of the cells that make up the water conducting tissues in some Nymphaeaceae, they hardly have the morphology of what are called vessel elements elsewhere, however, there are vessels of a variety of types in the roots in the stems of Brasenia. Hydatellaceae also have vessel elements with scalariform perforation plates, although these are absent from the leaves. The distinctive uniseriate trichomes found in all groups may secrete nectar or mucilage, or they may be involved in ion exchange (Vogel 1998a); Wilkinson (2006) calls the trichomes on the leaves, hydropotes. It is possible that there are epidermal oil cells in Nymphaeaceae (Wilkinson 2006); do they contain ethereal oils?
The inner bracts found in some Hydatellaceae and the inner petals of Cabomba are notably slow in developing (Rudall et al. 2007). If the corolla represents sterilised stamens, as some think, having external staminodes will probably be another synapomorphy at least for [Nymphaeaceae + Cabombaceae]. For discussion about the presence of a granular infratectum in Nymphaeales, see M. L. Taylor et al. (2013, 2015, also 2014 for other characters); the infractectum is generally columellate, how obviously so depending on the thickness of the infratectal space. Some genera in all families have exotestal cells that are neither very tall nor much thickened (Hamann et al. 1979; Collinson 1980). For the distinctive single-celled chalazal endosperm haustorium, see Rudall et al. (2009b). In general, the endosperm is slight and it probably functions as transfer tissue betweem embryo and perisperm (Friedman et al. 2012).
Phylogeny. Hydatellaceae are sister to Xyridaceae in Stevenson et al. (2000; see also Stevenson & Loconte 1995); both have latrorse anthers and an operculum "stopper" that is tegmic in origin. Trithuria and Xyris appear as sister taxa (weak support) and in turn sister to Mayaca (still weaker support), although other Xyridaceae are not immediately related (Michelangeli et al. 2003). However, although Bremer (2002) noted that Mayacaceae and Hydatellaceae might be weakly associated with Xyridaceae or Eriocaulaceae, depending on what taxa were included in the analysis, there were a number of long branches in this area and he excluded the first two families from his final analysis, while Janssen and Bremer (2004) suggested that the association of Hydatellaceae with Mayacaceae was probably an artefact (see also Chase et al. 2006).
More recent studies (Saarela et al. 2006, esp. 2007, several genes from two compartments, morphology: Friis & Crane 2007 [commentary]) place Hydatellaceae firmly with Nymphaeales, and sister to [Cabombaceae + Nymphaeaceae]; the sequence that placed Hydatellaceae in Poales was a chimaeric pcr recombinant involving a grass and a moss. Many of the morphological features of Hydatellaceae that made it so different from other monocots are consistent with this new position. Hamann (1998) had even noted that the antipodal cells were absent or degenerated early, and absence of these cells would almost be expected if Hydatellaceae were placed here, indeed, Friedman (2008a) and Rudall et al. (2008) found that Hydatellaceae had the distinctive 4-celled embryo sac of other Nymphaeales and Austrobaileyales.
Includes Cabombaceae, Hydatellaceae, Nymphaeaceae.
Synonymy: Barclayales Doweld, Cabombales Richard, Euryalales H. L. Li, Hydatellales Reveal & Doweld, Hydropeltidales Spenner - Hydatellanae Reveal, Nymphaeanae Reveal - Nymphaeidae Takhtajan - Hydropeltopsida Bartling, Nymphaeopsida Horaninow
HYDATELLACEAE U. Hamann, nom. cons. Back to Nymphaeales
(Plant annual), growth sympodial, rhizome short, erect; chemistry?; mycorrhizae 0; root stele monarch; cuticular waxes 0; leaves linear, with a single vein, margins entire; plant monoecious; inflorescence axillary, scapose (sessile), capitate, with involucral bracts; flowers very small, monosymmetric by reduction [necessarily so!]; P 0; staminate flowers: A 1, filaments long, slender; endothecium 0; tapetal cells?; pollen with spinules; carpellate flowers: pedicel articulated; G 1, three vascular bundles equidistant (2, 1), stigma penicillate, of rows of plump cells; extragynoecial compitum 0; ovule pendulous, anatropous, apotropous, micropyle bistomal, parietal tissue ca 2 cells across (?0), nucellar cap +/0; (two embryo sacs developing); fruit splitting into three valves, or achenial; exotestal cells with sinuous anticlinal walls, other layers ± collapsed, tanniniferous; embryo barely differentiated, suspensor unicellular; n = 7; seedling - see below.
1 [list]/10. India, New Zealand and Australia (map: from Cooke 1987; FloraBase 2004).
Age. It has been estimated that crown-group Hydatellaceae are (23.4-)19.1, 17.6(-14.7) m.y.o. (Iles et al. 2014).
The pollen Monosulcites riparius in ca 75-70 m.y.o. rocks from Eastern Siberia has been identified as Trithuria, but this must be a misidentification if the ages above hold.
Evolution: Divergence & Distribution. For the evolution and biogeography of the family - crown Hydatellaceae are certainly not Gondwanan in age - see Iles et al. (2014); Trithruria konkanensis (India) and T. lanterna (N. Australia) diverged (1.3-)0.76(-0.24) m.y.a. and evolution in the genus seems in general to be pretty active (e.g. Marques et al. 2016 and references).
Pollination Biology & Seed Dispersal. For reproductive ecology - wind-, self-, or hyphohydrous pollination - see M. L. Taylor et al. (2010); the pollen tubes grow down the multicellular hairs under the cuticle (Prychid et al. 2011).
Genes & Genomes. For chromosome numbers, see Marques et al. (2016).
Chemistry, Morphology, etc. The sieve tube plastids were reported as having triangular proteinaceous inclusions, but the inclusions appear to be of the starchy type as are more to be expected in this part of the tree (Tratt et al. 2009). There is some variation in the epidermis of the root and whether or not root hairs are produced (Sokoloff et al. 2008a). Hairs with possible apical secretory cells are known only from the inflorescences.
The inflorescence is described as being cymose and capitate, although bractless and with highly reduced flowers, i.e., it is a sort of pseudanthium, although alternative interpretations are possible (Rudall et al. 2007a, 2009a). The pedicels seem at least sometimes to be articulated. Early work suggested that the carpels might be initiated outside the stamens, and this has been confirmed (Rudall et al. 2007a); staminate flowers are the first to be initiated in the cymose inflorescence (see also Begoniaceae). However, how the reproductive structures are to be interpreted, whether flowers or inflorescences, is unclear, and Sauquet et al. (2017) elected not to include the family in their study of the morphology of the ancestral angiosperm flowers.
The fruit opens along three lines as the three vascular bundles separate from the rest of the pericarp (see also Sokoloff et al. 2013a). Both integuments have two cell layers; the operculum is formed from enlarged cells of the inner integument. Starch deposition in tissues that will become perisperm begins before fertilization (Friedman 2008a).
There is some disagreement over the interpretation of the morphology of the embryo. Tillich et al. (2007) compared it with that of a monocot, describing collar rhizoids, a coleoptile, two cotyledonary sheath lobes, and a haustorium. Sokoloff et al. (2008a) suggested that the sheathing structure with its bilobed apex that is found in some species could be interpreted as two more or less completely connate cotyledons. The rest of the embryo is attached to the sheathing structure, and a layer of endosperm is the intermediary between it and the perisperm (Friedman et al. 2012). In some taxa there is apparently no sheathing structure at all, only a haustorial lateral outgrowth (cotyledonary) that goes into the rest of the seed, the rest of the cotyledon being photosynthetic, so the seedlings are simultaneously both phanero- and cryptocotylar - c.f. some monocots (Sokoloff et al. 2013b)! Sokoloff et al. (2008a, 2014) suggested that Hydatellaceae showed how monocot-like embryos/seedlings might have originated. Both Tillich et al. (2007) and Sokoloff et al. (2008a) examined largely surface morphology, neither looked in any detail at anatomy (c.f. Friedman et al. 2012: superb micrographs; Sokoloff et al. 2014). Tuckett et al. (2010: discussion of "ancestral" embryo type for angiosperms must include Amborellaceae, at least; see also Sokoloff et al. 2014) found that the embryo differentiated and the shoot and root appeared only after germination began.
Meiosis during microsporogenesis has a number of odd features, and it is possible that (some of) the chromosomes are holocentric (Kynast et el. 2014).
Additional information is taken from Hamann (1998: general), Sokoloff et al. (2008b: family monograph), Cutler (1969: vegetative anatomy), Rudall et al. (2007a: flower/inflorescence development), Remizowa et al. (2008b: pollen), Hamann (1975) and Rudall et al. (2008a, both embryology, Cook (1983: germination), Hamann et al. (1979: seed anatomy), and Sokoloff et al. (2009a: growth patterns of the perennial species).
Previous Relationships. Hydatellaceae had long been considered to be monocots, largely because of their superficial similarity to Centrolepidaceae (= Restionaceae). Both groups are very reduced morphologically, and indeed Hydatellaceae have been misidentified as Centrolepidaceae. It was unclear if the gynoecium of Hydatellaceae was 1- or 3-carpellate, and since the fruits of Trithuria (= Hydatella) opened by three valves, they looked rather monocot-like. The combination of characters in Hydatellaceae was recognised as being unique to that group, and it made them very distinctive within monocots as a whole (e.g. Hamann et al. 1979; Dahlgren et al. 1985).
[Cabombaceae + Nymphaeaceae]: plant monopodial, rhizome/stolon elongated; hydroyzable [ellagi]tannins +; vessel elements in roots, with extensive fibrillar network in the end plates; pit membranes of tracheids with two thick layers of large fibrils; minute rhombic crystals on stellate cells [astrosclereids, stellate parenchyma cells]; leaves peltate, lamina vernation involute, secondary veins palmate, actinodromous, festoon brochidodromous, margin toothed, crenate or entire, (hydathodes +); flowers single; receptacle with cortical vascular system; P whorled, (outer [inner] whorls in 3's), outer members enclosing the rest of the bud; A whorled, (stamens in pairs opposite P members); tapetum (amoeboid), cells multinucleate; pollen tube growth moderately fast; carpel margins with postgenital fusion, placentation ± laminar; micropyle endostomal, parietal tissue 1-2 cells across, nucellar epidermal cells ± radially elongated, supra-chalazal tissue massive; mesocarp ± aerenchymatous; exotesta ± palisade, ± massively thickened, with sinuous anticlinal cell walls; endosperm bipolar, chalazal cell ± enlarged and elongated, haustorial, embryo suspensor often ± filamentous.
Age. There has been much discussion over the timing of diversification within the Cabombaceae-Nymphaeaceae clade (e.g. Nixon 2008), and dates from molecular and molecular analyses in part conflict strongly. Wikström et al. (2001: c.f. relationships) suggested that divergence of the two families occurred (152-)144, 111(-103) m.y.a., while the age in Magallón and Castillo (2009) is ca 112 m.y. (see also Tank et al. 2015: ca 112.5 m.y., that in Magallón et al. (2013) around 122.7 m.y., and that in Iles et al. (2014: [Amborellaceae + Nymphaeales]) (107.1-)102.1(-98.8) m.y. ago. However, Löhne et al. (2008) thought that divergence was only Palaeocene in age, (75-)56.4(-38) m.y.a., while Bell et al. (2010) offered a still younger date of (56-)42, 38(-25) m.y.; Yoo et al. (2005) pegged the crown group age to 44.6 ± 7.9 m.y. and Naumann et al. (2013), at around 94.75 m.y., suggested an intermediate age.
Early fossil-based estimates for the age of this group were only ca 90 m.y. (Crepet et al. 2004), but substantially earlier dates are likely (Friis et al. 2009b). There are fossils of stem-group Nymphaeaceae, Cabombaceae and/or [Nymphaeaceae + Cabombaceae] from the Lower Cretaceous and from several parts of the world (e.g. D. W. Taylor et al. 2001, 2008; Friis et al. 2011). Although other fossils possibly of this group (to a certain extent characters of the two families are combined) are known from the Barremian-Aptian deposits 125-113 m.y.o. in Portugal (Friis et al. 2001), they may also be from a member of Austrobaileyales (Gandolfo et al. 2004); see also von Balthazar et al. (2008) for another fossil perhaps assignable to this general [Nymphaeales-Austrobaileyales] area. A dozen or more genera based on fossil seeds have been described in this area (Friis et al. 2017b and references). D. W. Taylor et al. (2008, see also Taylor 2008) noted how inclusion of different fossils affected ideas of relationships.
Pluricarpellatia, probably to be placed in or near Cabombaceae (Doyle & Endress 2014), is known since the Early Crtetaceous (Mohr et al. 2008). The Early Cretaceous Monetianthus was embedded within crown Nymphaeaceae in morphological analyses (Friis et al. 2009b, but c.f. 2011; see also Doyle & Upchurch 2014; Doyle 2016), and this may be true for the mid-Albian Carpestella, from Virginia (Doyle & Endress 2014); both these genera have very small flowers. The distinctive reticulate-perforate pollen of Monetianthus would then be independently derived within Nymphaeales, but other analyses also placed the genus at the node above Nymphaeales along the spine of the angiosperm tree (Friis et al. 2009b). Yoo et al. (2005) thought that the fossil Microvictoria was perhaps stem group Nymphaeales (c.f. Gandolfo et al. 2004; Endress 2006; Friis et al. 2011).
Evolution: Divergence & Distribution. D. W. Taylor et al. (2008, see also Taylor 2008) discuss the vegetative evolution of the group (see some of the characters above); the inclusion of different fossils affected relationships, and hence evolutionary interpretations, in analyses of morphological variation. Friis et al. (2011: fig. 20.2) discussed diversification in this clade in some detail, assigning many Palaeogene fossils to the two families; see also D. W. Taylor et al. (2001) for fossils of Cabombaceae.
Ecology & Physiology. Nymphaeales, along with other angiosperms, may have dominated aquatic habitats in Europe by the Albian ca 105 m.y.a. (Sender et al. 2010).
Pollination Biology & Seed Dispersal. Generalist pollination is common in this clade (Gotttsberger 2016).
Genes & Genomes. For the chloroplast inverted repeat, see Graham and Olmstead (2000).
Chemistry, Morphology, etc. For micromorphological details of vessels and tracheids, see Carlquist and Schneider (2009) and Schneider et al. (2009); details of the wall structure of tracheids, at least, are very distinctive. Note that Carpenter (2005) described stomata as being largely variants of the actino/stephanocytic types; only one member of Cabombaceae was studied. D. W. Taylor (2008) outlined the vegetative morphology of this clade.
The flowers are often not strictly axillary. Warner et al. (2008, 2009) discuss perianth evolution, and in Warner et al. (2008) there is a useful summary on the literature on perianth morphology. Zini et al. (2016) described the distinctive nucellar epidermis of the ovules as being an epistase.
For information on anatomy, see Gwynne-Vaughan (1897), for more on vessels and tracheids, see Schneider and Carlquist (2009a, b), for root epidermis, see Voronkina (1974: ordinal characterisation above), for root anatomy, see Seago (2002), for perianth venation, Hiepko (1965b), for pollen morphology, Osborn et al. (1991), for embryo sac development, Orban and Bouharmont (1998), for endosperm evolution, Floyd and Friedman (2001), for ovule development, Yamada et al. (2001b), for pericarp anatomy, Yatzenko et al. (2012), for seed anatomy, see Collinson (1980) and Chen et al. (2004), and for general information, Les et al. (1999) and Schneider et al (2003).
Phylogeny. For a morphological phylogeny of the clade, see Taylor (2008).
CABOMBACEAE A. Richard Back to Nymphaeales
Alkaloids 0; root stele monarch; stem vascular tissue with two pairs of bundles; internodes long; flowers rather small, parts whorled, (2)3(4)-merous, polysymmetric [hexamerous]; P = two whorls of T, petal-like, members with single trace; filaments moderately slender; tapetum more or less amoeboid; pollen endexine lamellate when young, not when mature; pollen tube growth intra-gynoecial; when G 3 or more, inner whorl of three ± opposite petals, three vascular bundles equidistant, stylar neck +, stigma papillate; extragynoecial compitum at least initially 0; ovules 1-3(-5)/carpel, attached variously, outer integument semi-annular [hood-shaped], hypostase +; hilum and micropyle sharing same opening in center of operculum; micropylar endosperm cell alone with free-nuclear divisions [endosperm helobial], chalazal cell protruding into the perisperm; germination?
2 [list]/6 - two genera below. World-wide, rather scattered, Brasenia schreberi subfossil remains show it to be far more widespread in Europe than at present (map: from Raymond & Dansereau 1949; Fassett 1953; Ørgaard et al. 1992; Hultén 1961; Fl. N. Am. III 1997; Trop. Afr. Fl. Pl. Ecol. Distr. 1. 2003, 6. 2011; Löhne et al. 2008). [Photo - Brasenia Habit] [Photo - Flower.]
Age. Bell et al. (2010) suggested that the two genera diverged (31-)21, 20(-10) m.y.a.; other estimates are (109-)101(-93) and (75-)67, 60(-52) m.y. (Wikström et al. 2001).
Pluricarpellatia, probably Cabombaceae, is known from rocks 115 m.y.o. in northeast Brazil (Mohr et al. 2008).
1. Cabomba Aublet
Plant with horizontal branching floating stems; submerged leaves usually oposite or whorled, lamina deeply palmately (subdichotomously) dissected, lobes linear; inner P whorl somewhat delayed in development, with nectaries; A 3, 6, extrorse; pollen trichotomocolpate, tectum continuous, striate; G 1-4(-7), (basally connate), stigma capitate; fruit follicular; seeds 2-3, spiny; exotestal cells low, walls not much thickened; x = 13.
1/5. New World; warmer areas.
2. Brasenia Schreber
Plant rhizomatous, with ± vertical stems; stems encased in thick layer of mucilage, paired, glandular patches at nodes; leaves spiral; A many; pollen scabrate; G 4-18, stigma elongate; seed achenial, 1-2-seeded; n = 40.
1/1: Brasenia schreberi. Scattered, tropical and (warm) temperate, but also S.E. Australia and S.E. Siberia.
Evolution: Pollination Biology & Seed Dispersal. Brasenia is wind pollinated, while Cabomba has paired nectaries on its inner tepals and is pollinated by flies. M. L. Taylor and Williams (2009) describe details of reproduction of Cabomba from pollination to fertilization, while Schneider and Jeter (1982) discuss its pollination. For more details, see Erbar (2014) and Gottsberger (2016)
Chemistry, Morphology, etc. The root endodermis has a Casparian strip and suberin lamellae. It is unclear how to interpret nodal anatomy. In Cambomba a trace leaves from each member of a vascular budle pair which shortly thereafter fuse commissurally, creating a nodal plexus; the foliar traces fuse and then divide, providing two petiolar bundles (Moseley et al. 1984). The peltate leaves are spirally arranged, although in some taxa they are uncommon; the more or less dichotomously-divided submerged leaves are opposite.
There are five vascular bundles in the sepals and three vascular bundles in the petals of Cambomba, in both cases there is a single trace leaving the floral axis (Moseley et al. 1984). Stamens are sometimes physically close to each nectary and then they appear paired (Ørgaard et al. 1992). Pollen of Cabomba has striate exine. Although the endexine of mature pollen of Brasenia schreberi is not lamellate, it is laid down in plates (M. L. Taylor & Osborn 2006).
The granular infratectum of Podostemaceae has been compared with that of Cabombaceae; both are aquatics (Passarelli et al. 2002).
Some information is taken from Williamson and Schneider (1993: general), Richardson (1969: development of Brasenia flowers), Erbar (2014: nectary), Khanna (1965) and Batygina et al. (1982), both embryology, Floyd and Friedman (2000: endosperm development), and M. L. Taylor et al. (2008: esp. pollen).
Synonymy: Hydropeltidaceae Dumortier
NYMPHAEACEAE Salisbury Back to Nymphaeales
Perennials (annuals); myricetin, sesquiterpene [pseud]alkaloids; a root arises below each leaf; root stele polyarch; stem vascular tissue complex, (in concentric rings), axial bundles concentric; astrosclereids +; nodes 3:3; flowers neither terminal nor axillary [often replace leaf in spiral], large, haplomorphic; P members usu. with sepaloid and petal-like areas; A many, often whorled, laminar, the staminal bundle branched from near base in thecal region, staminodes +, next to G, (also next to P), (filaments stout), connective produced or not; tapetum both glandular and amoeboid; microsporogenesis simultaneous; (pollen tricellular), (no exine), membranous granular layer + [innermost endexine]; G laterally connate, whorled, postgenital margin fusion complete, stigma dry; ovules many/carpel (-3), not filling the locule, outer integument also cap-shaped [annular]; embryo sac ± 8-shaped [?level]; fruit baccate; testa between micropyle and hilum; micropylar endosperm chamber with cellular divisions, endosperm scanty, embryo chlorophyllous or white, broad and plug-like, (large).
3 [list]/58 - two groups below. World-wide (map: from Vester 1940; Wickens 1976; Hultén 1961; Trop. Afr. Fl. Pl. Ecol. Distr. 1. 2003; Heywood 2007; Löhne et al. 2008). [Photo - Leaf, Flower.]
Age. E. L. Schneider et al. (2004) suggested an age for the family of ca 121 m.y.a., Magallón et al. (2013) an age of around 100.1 m.y., while Iles et al. (2014) suggested an age of (99.6-)95.5(-92.9) m.y. ago. However, estimates in Bell et al. (2010) are only (49-)32, 29(-15) m.y. and those in Zhou et al. (2014) (60.6-)28.2(-3.8) m.y., while those in Naumann et al. (2013) are around 51.8 or 40.8 m.y., somewhat intermediate.
The Late Aptian/Early Albian Cretaceous Monetianthus, from Portugal, is embedded in Nymphaeaceae in morphological analyses (Friis et al. 2009b). Microvictoria, a somewhat later fossil from the Turonian ca 90 m.y. old and found in New Jersey, U.S.A., is very like Victoria (= Nymphaea). Victoria has "paracarpels" immediately surrounding the gynoecium, and these are also found in Microvictoria; indeed, flowers of this latter are like those of Victoria in almost all respects, although they are less than 1/10th their size (Gandolfo et al. 2004). Jaguariba is assignable to crown group Nymphaeaceae; it is from the Aptian Crato flora of northeast Brazil and is some 115 m.y.o. (Coiffard et al. 2013a). For Cecilanthus, from early Cenomanian Maryland ca 100 m.y.a., see Herendeen et al. (2016) and above).
1. Nupharoideae Ito
Rhizomes stout, horizontal, creeping; indolizidine alkaloids +; roots with 10-18 xylem poles, pith large; bracts +; P dimorphic, 1-veined, outer members 5-14, spiral, the outer greenish, the inner coloured, inner tepals many, small, petal-like, somewhat delayed in development; nectary on abaxial surface of inner tepals; anthers valvate [H-dehiscence], connective strongly produced; pollen grains tricellular, spiny, tectum continuous, aperture operculate; G 5-23(-36); outer integument 4-6 cells across, parietal tissue ca 2 cells across, nucellar cap ca 4 cells across, hypostase, postament +; fruit emergent; micropyle and hilum very close; seeds hairy, exotestal cells with straight anticlinal walls; n = 17.
1/11. North Temperate.
Age. Friis et al. (2017b) were inclined to group Notonuphar, fossil seeds from Eocene Seymour Island, Antarctica, with Nuphar, although it has tall, thick-walled testal cells like those of Brasenia (Cabombaceae).
Synonymy: Nupharaceae A. Kerner
2. Nymphaeoideae Arnott
(Mycorrhizae +); (rhizome short, erect); phloem loading active, cells walls smooth, no plasmodesmata; roots with 5-9 xylem poles, pith at most small; vegetative buds not axillary; (spines on pedicel, lower surface of lamina, etc.); stipules +, adaxial or lateral; inner satellite peduncle bundle +; bracts 0; hypanthium ± developed; P members 3-veined, K 4-5, spiral, (C 0 - some Nymphaea ondinea); intermediates between A and C; (outer staminodes +, showy, inner staminodes + - Victoria); (staminal bundle unbranched, esp. in smaller inner A); pollen (in tetrads), (bicellular), with encircling sulcus ["ring like aperture", "zonasulcate"], (inaperturate), surface various, inc. tectum continuous, infratectal space usu. small, columellae inconspicuous; G 3-many, ± inferior [A alone on top of G, K and "C" also often on top; A also adnate to "C"], with inter-carpel septal slits, central pool of stigmatic fluid, floral axis projecting in the middle [not Barclaya], stigmatic surface continuous; ovules (straight - Barclaya), (micropyle bistomal), (outer integument 4-5, ca 20 cells across [Euryale]), (parietal tissue 3-4 cells across - Victoria ); seeds arillate (not, but spiny - Barclaya), (exotestal cells cuboid, anticlinal walls straight - Euryale); (embryo suspensor 0); n = 10, 12, 14-18.
2/48: Nymphaea (46). World-wide.
Synonymy: Barclayaceae H.-L. Li, Euryalaceae J. Agardh
Evolution: Divergence & Distribution. The family is thought to have been much more diverse in earlier epochs, and distinctive seeds with a micropylar and palisade exotesta with sinuous anticlinal walls that can be assigned here being common in the Cretaceous (Friis et al. 2009b, 2011, 2017b; see also above). Recently, fossils assigned to crown group Nymphaeaceae (as Jaguariba) have been found in the Aptian Crato flora, some 115 m.y.o. in northeast Brazil (Coiffard et al. 2013a) and the first seeds from the Southern Hemisphere have been described in Eocene deposits from Seymour Island, Antarctica (Friis et al. 2017b).
Indeed, although the family is widespread and probably very old, individual clades within it are relatively localized, and it has even been suggested that crown group diversification may have occurred in the northern hemisphere in the early Caenozoic (Löhne et al. 2008; see also Friis et al. 2011).
Pollination Biology & Seed Dispersal. Thermogenesis has been detected in the flowers of some Nymphaeaceae (Seymour 2001; Seymour & Matthews 2006). Beetles and a variety of other insects, including flies, are pollinators (e.g. Gandolfo et al. 2004; Padgett 2007; Thien et al. 2009). Scarab beetles (Cyclocephalini) may have pollinated night-flowering water lilies for some 100 m.y.; they pollinate species both in America, where the beetles are common, and in Africa, where the beetles are otherwise very uncommon (Ervik & Knudsen 2003; Moore & Jameson 2013). Beetle pollination may have occurred even in the early small-flowered members of the fammily (M. L. Taylor et al. 2013 and references). The distinctive flowers of Ondinea (= Nymphaea ondinea), wind pollinated, are derived from Nymphaea-type flowers (Löhne et al. 2009). Schneider (1979) summarized information about the pollination biology of the family; see also Erbar (2014), and for much detail, Gottsberger (2016: Table 2).
The progamic phase, the time between pollination and fertilization, is notably short, up to a mere 8 hours, as in at least some other aquatic angiosperms (including Nelumbo: see Williams et al. 2010).
Dehiscence of the fruit of Nymphaeoideae is by swelling of the mucilage inside it, whereupon the wall splits irregularly.
Plant-Animal Interactions. Nymphaeaceae are host plants of reed beetles, Chrysomelidae-Donaciinae (see also Poales: Kölsch & Pedersen 2008: much discussion on the age and evolution of the group). Interestingly, Enterobacteriaceae near Buchnera are believed to produce the material that makes up the cocoon that characterises Donaciinae, a group that is also noted for the ability of the larvae to grow under water (Kölsch & Pedersen 2010).
Genes & Genomes. A genome duplication in Nuphar is estimated to have occurred (76.8-)72.8(-67.9) m.y.a. (Vanneste et al. 2014b).
Chemistry, Morphology, etc. The root endodermis has a Casparian strip. There are sometimes sclerenchymatous diaphragms in the pith. The vasculature of the stem is exceedingly complex, especially at the node, with peduncular complexes forming internally, however, basic stem structure is unlike that of monocotyledons; the primary xylem is mesarch (Weidlich 1980 and references). Schneider et al. (2008, 2009) and Schneider and Carlquist (2009) discuss stem tracheids and root vessels, emphasizing the rather arbitrary distinction between vessels and tracheids; Carlquist (2012c) suggested that there were no vessels. The astrosclereids of Nuphar and Nymphaea, at least, have calcium oxalate crystals in the walls (Fink 1991). Stipules may be adaxial and bicarinate or paired and lateral.
In both Nuphar and Nymphaea flowers and even branches may replace leaves in the genetic spiral (e.g. Cutter 1957a, b; Groß et al. 2006). Cutter (1957b) noted that the leaf apparently subtending the flower of Nuphar was in fact born on the flower stalk; if a prophyll, it should be noted that it is abaxial in position! For discussion as to whether or not Nuphar has bracts, see Schneider et al. (2003).
Flower parts are generally whorled (see Endress & Doyle 2015 and references). Yoo et al. (2010) discuss the evolutionary/developmental relationship between sepals and petals; see also Doyle and Endress (2011), who suggest that Nuphar has both tepals and petals. Schneider (1976) and Moseley and Uhl (1985) note that the vascular supply to perianth and androecial members consists of two radially associated bundles. In Euryale the filaments are quite slender and are basally adnate to the staminodes; it is unclear if it has free nuclear endosperm (Floyd & Friedman 2001 - see also Kanna 1964, 1967 for endosperm development in the family). Weberling (1989) suggested that in at least some Nymphaeaceae the individual carpels were free laterally, if adnate to the central axis inside and to "hypanthial" tissue outside (see also von Balthazar et al. 2008). The ovules of Victoria and Euryale are massive affairs (Zini et al. 2016). Zhou and Fu (2008) found that at anthesis, but not before or after, the micropyle of Nuphar was bistomal, not endostomal. Weberling (1989) also described how in Nuphar axial tissue separates from the gynoecium when the fruits are ripe, so exposing the basically free carpels; if this is correct (but it seems rather unlikely), its gynoecium would be very similar to that of other Nymphaeaceae; Padgett (2007) described dehiscence as being along lines in the septal and ovarian walls where aerenchymatous tissue had developed. For embryo development and germination in Nymphaea, see Baskin and Baskin (2007b), the embryo may be fully developed before germination begins. The seedling axis of some species of Nymphaea have a lateral projection.
Some information is taken from Schneider and Williamson (1993: general); see Moseley (1958) for stamen morphology, Yao et al. (2004), M. L. Taylor et al. (2012, 2013) and Coiro and Lumaga (2013), all pollen morphology, for ovules, Zini et al. (2014b) and Shamrov (1998: Nuphar), Floyd and Friedman (2001) endosperm development, Povilus et al. (2015: embryology and endosperm), Takhtajan (1988) and Losada et al. (2014) ovules and seeds, Khanna (1964, 1967) embryology (8-nucleate embryo sacs...), Cook (1909) embryology, and Tillich (1990) seedling morphology. For Nuphar, see Padgett (2007).
Phylogeny. Nymphaea s. str. was monophyletic in a phylogenetic analysis of vegetative characters, but without much support (D. W. Taylor 2008). Y.-L. Liu et al. (2005) provide an ITS phylogeny of the family, but with some rather surprising relationships - [Nuphar [Cabomba + Brasenia] [Nymphaea [Euryale + Victoria]]]. Nelumbo, which was included in the analysis, did at least stay outside this clade... For a phylogeny of Nymphaea, see Borsch et al. (2007, 2012); the genus definitely includes the wind-pollinated and usually apetalous Ondinea, but some relationships lacked much support, e.g. the position of [Euryale + Victoria] as sister to Nymphaea s.l.. However, in some studies the spiny Victoria and Euryale are embedded in Nymphaea s.l. (Löhne et al. 2007, 2009; Borsch et al. 2008; c.f. Friis et al. 2011).
Classification. A broad circumscription for Nymphaea seems the best solution.