EMBRYOPSIDA Pirani & Prado (crown group)
Gametophyte dominant, independent, multicellular, thalloid, with single-celled apical meristem, showing gravitropism; cuticle +; cell walls with (1->4)-ß-D-glucans [xyloglucans], lignin +; rhizoids unicellular; several chloroplasts per cell; 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, centrioles develop de novo, associated with basal bodies of flagellae, multilayered structure +, proximal end of basal bodies lacking symmetry, stellate pattern associated with doublet tubules of transition zone; spermatozoids with a left-handed coil; male gametes with 2 lateral flagellae; oogamy; diploid embryo initially surrounded by haploid gametophytic tissue, plane of first division horizontal, suspensor/foot +, cell walls with nacreous thickenings; sporophyte multicellular, sporangium +, single, with polar transport of auxin, 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 multilaminate]; spores trilete [?level]; close association between the trnLUAA and trnFGAA genes on the chloroplast genome.
Note that many of the bolded characters in the characterization above are apomorphies in the streptophyte clade along the lineage leading to the embryophytes rather than being apomorphies of the embryophytes.
Abscisic acid, ?D-methionine +; sporangium with columella; stomata +, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; polar transport of auxins and class 1 KNOX genes expressed in the sporangium alone; MIKC, MI*K*C* and class 1 and 2 KNOX genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns.
[Hornworts + Polysporangiophyta]: archegonia embedded in the gametophyte; sporophyte long-lived, chlorophyllous, nutritionally largely independent of the gametophyte; sporophyte-gametophyte junction interdigitate, sporophyte cells showing rhizoid-like behaviour; spores trilete.
Sporophyte well developed, branched, free living, sporangia several; apical meristem +.
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Photosynthetic red light response, passive control of leaf hydration; (condensed or nonhydrolyzable tannins/proanthocyanidins +); vascular tissue +, sieve cells +, tracheids +, in both protoxylem and metaxylem; endodermis +; root xylem exarch [development centripetal]; stem with an apical cell; leaf blade with mean venation density 1.8 mm/mm2 [to 5 mm/mm2]; sporangia adaxial on the sporophyll, lacking columella, eusporangiate [sporangia derived from periclinal divisions of several epidermal cells, wall multilayered]; stellate pattern split between doublet and triplet regions of transition zone; placenta with single layer of transfer cells in both sporophytic and gametophytic generations, embryo with roots arising lateral to the main axis [plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Branching ± monopodial; lateral roots +, endogenous, root cap +; tracheids with scalariform-bordered pits; leaves spirally arranged, 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; male gametes multiflagellate, basal bodies staggered, blepharoplasts paired; chloroplast long single copy ca 30kb inversion [from psbM to ycf2].
Plant woody; lateral root origin from the pericycle, root apex multicellular; endodermis +; shoot apical meristem multicellular; lateral meristems +, 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 with xylem and phloem originating on alternate radii, vascular tissue not medullated, cork cambium deep seated; arbuscular mycorrhizae +; 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 +; stem cork cambium superficial; branches exogenous; 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.; leaves with petiole and lamina, spiral, development basipetal, blade simple; axillary buds +, not associated with all leaves; prophylls two, lateral; plant heterosporous, sporangia borne on sporophylls; microsporophylls aggregated in indeterminate cones/strobili; true pollen +, grains mono[ana]sulcate, exine and intine homogeneous; ovules unitegmic, parietal tissue 2+ cells across, megaspore tetrad linear, functional megaspore single, chalazal, lacking sporopollenin, megasporangium indehiscent; male gametophyte development first endo- then exosporic, 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; seeds "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; embryo cellular ab initio, endoscopic, plane of first cleavage of zygote transverse, suspensor +, short-minute, embryo axis straight, so shoot and root at opposite ends [plant allorhizic], white, 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.
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, 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, secondary veins pinnate, overall growth ± diffuse, venation hierarchical-reticulate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic, 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], ± embedded in the filament, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally, 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 thin, compact, lamellate only in the apertural regions; nectary 0; carpels present, superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus short, 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 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 binucleate at dispersal, mature male gametophyte trinucleate, germinating in less than 3 hours, pollination siphonogamous, tube elongated, growing between cells, growth rate 20-20,000 µm/hour, outer wall pectic, inner wall callose, 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, flagellae 0, double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; seed exotestal, becoming much larger than ovule at time of fertilization; endosperm diploid, cellular [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; embryogenesis cellular; dark reversal Pfr -> Pr; Arabidopsis-type telomeres [(TTTAGGG)n]; 2C genome size 1-8.2 pg [1 pg = 109 base pairs], whole nuclear genome duplication [epsilon duplication], 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; PHYE +. Back to Main Tree
Age. Wikström et al. (2001) suggested an age of (172-)165, 147(-140) m.y. for this node (see Magallón 2009 for other early dates), while ages in Bell et al. (2010: BEAST exponential and lognormal respectively) are (187-)173(-160) or (150-)144(-138) m.y.; Soltis et al. (2008) give dates of some 174-127 m.y. and Moore et al. (2010: 95% highest posterior density) ages of (151-)144(-138) m.y.. Magallón and Castillo (2009) offer very divergent estimates - ca 235.5 and 129.7 m.y. for relaxed and constrained penalized likelihood datings respectively. Clarke et al. (2011: 95% credibility intervals) suggest ages of (208-)177(-152) m.y., N. Zhang et al. (2012; see also Xue et al. 2012) ages of (185-)161(-146) m.y., and Magallón et al. (2013) an age of around 170.4 m.y..
A fossil-based estimate for the age of this clade is ca 113 m.y. (Crepet et al. 2004).
Chemistry, Morphology, etc. See Hegnauer (1990) for a discussion of the chemistry of the Polycarpicae, which also includes the magnoliids and Ranunculales. The sampling for the presence/absence of tension wood is poor, for instance, only one member of Austrobaileyales is mentioned in Höster and Liese (1966). Cuticular striations occur only above this node (Upchurch 2013).
Columellar infratectal structure of pollen grains may be best optimised here; the plesiomorphic condition is granular, also found in the pollen of several Magnoliales, Monimiaceae, etc., as reversals (Doyle et al. 1990b). For the 12BP deletion, see S. Kim et al. (2003, 2004b) and Aoki et al. (2004).
AUSTROBAILEYALES Reveal Main Tree.
Tiglic acid +; vessels solitary; nodes 1:2; petiole bundle(s) arcuate; lamina margin?; outer integument 5-7 cells thick; fruit a berrylet; P deciduous; mesotestal cells ± sclerotic; endosperm starchy, also proteins and lipids. - 3 families, 5 genera, 100 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...
Age. Wikström et al. (2001) suggested an age of (155-)148, 133(-126) m.y. for crown Austrobaileyales, Schneider et al. (2004) suggest ages of 168 and 85 m.y., Magallón and Castillo (2009) ages of ca 203 and 125 m.y., Bell et al. (2010) suggest ages of (145-)122(-99) or (130-)114(-110) m.y., and Magallón et al. (2013) thought that this node might be 103.4 m.y. old.
Evolution. Pollination Biology & Seed Dispersal. For a survey of what is known about pollination in the clade, see Thien et al. (2009).
Chemistry, Morphology, etc. The wood has paratracheal parenchyma (Carlquist & Schneider 2001). Laterocytic stomata are common in the order, and the cuticle surface is radiate-striate around the secretory cells on the lower surface of the leaf blade in Austrobaileyaceae and Schisandraceae, at least (Baranova 2004b for discussion; Carpenter 2006).
For vegetative anatomy, see Metcalfe (1987), for some developmental morphology of ovules and seeds, inc. details of lobing, etc., at micropyle, see Yamada et al. (2003a). For embryo sac and endosperm development, see Floyd and Friedman (2001), Friedman et al. (2003), Williams and Friedman (2004) and Tobe et al. (2007).
Phylogeny. For the circumscription of the order, see Soltis et al. (1997) and Källersjö et al. (1999); Trimeniaceae are also to be included (e.g. Qiu et al. 1999). Austrobaileyaceae are sister to the other members of the order.
Includes Austrobaileyaceae, Schisandraceae, Trimeniaceae.
Synonymy: Illicineae J. Presl - Illiciales Cronquist, Schisandrales Martius, Trimeniales Doweld - Schisandrineae Shipunov - Austrobaileyanae Chase & Reveal, Illicianae Doweld, Trimenianae Doweld - Illiciidae C. Y. Wu
AUSTROBAILEYACEAE Croizat, nom. cons. Back to Austrobaileyales
Liane, climbing by twining; alkaloids 0, flavonols?; primary stem with separate bundles; wood with broad rays; sieve elements with non-dispersive protein bodies; (stomata anomocytic); leaves ± opposite, lamina vernation conduplicate, margins entire, petiole short; flowers axillary, large [ca 5 cm across], cortical vascular system?; P 12-24; A 6-11, laminar, anthers embedded in connective, staminodes internal, 6 or more; G (4-)6-9(-14), stigma bilobed at apex; ovules (4-)6-8(-14)/carpel, apotropous; seeds ruminate, perichalazal; testa multiplicative, vascularized, sarcotesta +, outer mesotesta lignified; endosperm ?development; n = 22, ?23; germination epigeal.
1[list]/2. Australia (map: from Heywood 1978). [Photo - Flower.]
Chemistry, Morphology, etc. There is some discussion as to whether the highly inclined end walls of the sieve tube have sieve plates, or not (Evert 2006: 393 for literature); in any event, other details of the sieve connections are typically angiosperm. The stylar canal is filled with secretion.
See Bailey and Swamy (1949) for general morphology and anatomy, Behnke (1986: phloem anatomy, pores very narrow), Endress (1980a, 1984) for floral morphology, Carlquist (2001) for wood anatomy; some other information is taken from Endress (1993).
[Schisandraceae + Trimeniaceae]: flowers <3 cm across; pollen other than mono[ana]sulcate; infra-stylar extra-gynoecial compitum/pollen tube growth; stigma dry; megaspore mother cells 2-many; exotesta ± palisade.
Age. Anacostia, a fossil with graded-reticulate monosulcate to trichotomosulcate pollen and exotestal seeds from Cretaceous (Barremian-Aptian) deposits some 130-115 m.y. old of E. North America and Portugal (Friis et al. 1997b), may be sister to Schisandraceae (Doyle & Endress 2010).
SCHISANDRACEAE Blume, nom. cons. Back to Austrobaileyales
Tetracyclic triterpenes [cycloartanes], flavonols +, flavones 0, tanniniferous; primary stem ± with vascular cylinder; true tracheids +; astrosclereids +; mucilage cells +; (leaf epidermis silicified); lamina vernation supervolute; A 4-many, latrorse to introrse, pollen tricolpate, syncolpate pole distal, semitectate-reticulate, muri tall; stigma dry; exotesta with sinuous anticlinal cell walls, ?lignified mesotesta; n = 13, 14.
3/92. Sri Lanka and South East Asia to W. Malesia, S.E. U.S.A., E. Mexico, Greater Antilles.
Age. Magallón et al. (2013) suggested an age for crown-group Schisandraceae of around 42.2 m.y., and estimates are slightly under 50 m.y. in N. Zhang et al. (2012). Ages in Morris et al. (2007) are very different, the age being around 131.7 m.y., while those in Wikström et al. (2001) at (119-)108, 93(-82) m.y. are somewhat intermediate, as are those in Bell et al. (2010), at 91-89 m.y.. The latter two ages are likely to be underestimates if the identity of the trimeniaceous fossil seed (see below) is correct.
Shrubs or trees; plants Al accumulators; (pits vestured); nodes 1:1; branching on previous innovation; leaves pseudoverticillate, lamina margins entire; P (7-)12-many; G (5-)7-15(-21), pseudo-whorled around axis, occlusion also by postgenital fusion; ovule 1/carpel, near basal, parietal tissue ca 6 cells across; fruit an explosive follicle; seed with a circular cap; testa multiplicative; endosperm lacking starch.
1/42. South East Asia to W. Malesia, S.E. U.S.A., E. Mexico, Greater Antilles (map: from Wood 1972). [Photo - Flower, Fruit.]
Age. Morris et al. (2007) suggested that crown group Illicium was (91.5-)89.4, 76.3(-72.2) m.y. old.
Synonymy: Illiciaceae Berchtold & Presl nom. cons.
Schisandra Blume + Kadsura Jussieu
Lianes, climbing by twining; (silicon concentration high); distinctive neolignans, myricetin +; vessel elements with simple perforation plates; nodes 1:3; sclereids fibre-like, with crystals in the walls; stomata also laterocytic; leaves (two-ranked), lamina (vernation involute), teeth with clear persistent swollen cap into which proceed higher order veins as well as secondaries or tertiaries (margins entire); plant monoecious or dioecious; P 5-15, A 4-7, ± connate, endothecium biseriate; pollen heteropolar, (6 colpate); G 12-many, stigma papillate; ovules 2-5(-11)/carpel, parietal tissue 2-3 cells across, nucellar cap ca 2 cells across; (more than one embryo sac developing); berrylets usu. 2-seeded, receptacle enlarging greatly; endotesta also lignified; cotyledons convolute; n also = 7.
1-2[list]/50. Sri Lanka, East Asia to W. Malesia, S.E. U.S.A., Mexico (map: from Saunders 1998, 2000).[Photo - Infructescence.]
Synonymy: Kadsuraceae Radogizky
Evolution. Pollination Biology & Seed Dispersal. Illicium, Schisandra glabra (Schisandra s. str.) and Kadsura longipedunculata all have thermogenic flowers (Seymour 2001; Liu et al. 2006; Yuan et al. 2008); pollen may be a floral reward for the pollinator, and/or deceit may be involved. For the growth of the pollen tube through mucilage on the surface of the epidermis rather than between cells, i.e. the presence of an extragynoecial compitum, and the nature of the stigma surface, see E. G. Williams et al. (1993), Lyew et al. (2007) and Du and Wang (2012).
Romanov et al. (2013) discuss the the explosive dehiscence of the follicle of Illicium and its distinctive anatomy.
Chemistry, Morphology, etc. The vessel member endings of Illicium may also be reticulate. The prophylls of Schizandra are reported to be adaxial (Keller 1996); those I have seen are lateral.
The anther connective is especially well developed. The pollen is modified monosulcate (via trichotomonosulcate). The endotegmen may persist (Corner 1977).
Some general information is taken from Bailey and Nast (1948), Keng (1993), and Saunders (1997, 2000), Sy et al. (1997) discuss phytochemical relationships, Floyd and Friedman (2001) outline endosperm development, while Swamy (1964a: embryo sac unlike any others he knew), Friedman et al. (2003a, esp. b) and Friedman and Williams (2004) provide information on the female gametophyte. For floral development, see Robertson and Tucker (1979), Tucker and Bourland (1994) and Dong et al. (2012), for wood anatomy, see Yang and Lin (2007) and for pollen morphology, see Wang et al. (2010).
Phylogeny. Kadsura may be paraphyletic, based on the analysis of both trnL-F and ITS sequences, although paraphyly is not found in morphological analyses (Hao et al. 2001; Denk & Oh 2006; Liu et al. 2006). Liu et al. (2006) discuss character evolution in this group. Molecular and morphological studies also suggest rather different relationships within Illicium (Hao et al. 2000; Oh et al. 2003).
Classification. There is the option in A.P.G. II (2003) of placing the two parts of this quite well characterised clade in separate families, but combination seems in order (A.P.G. III 2009).
TRIMENIACEAE Gibbs, nom. cons. Back to Austrobaileyales
Trees or lianes; 5-O-methyl flavonols, flavones +, alkaloids?; primary stem with separate bundles; (vessels in radial multiples); rays 6-9-seriate; (secondary phloem with broad rays); mucilage cells +; leaves opposite, lamina margins entire or toothed; inflorescence axillary (terminal), branched; plants monoecious or flowers perfect; receptacle small; P 2-many, outer in pairs, otherwise spiral; A 6-25, anthers latrorse to extrorse (± introrse), connective somewhat prolonged; pollen disulcate, polyporate or inaperturate, monads or tetrads, endexine lamellate; G 1 (2), style 0, stigma ± penicillate; ovule 1/carpel, pendulous, micropyle bistomal, parietal tissue 9-30+ cells across, nucellar cap ca 6 cells across, hypostase +; megaspore mother cells at base of nucellus, embryo sac much elongated (few), reaching micropyle; seed with a circular cap; testa vascularized, almost all cell walls thick, outer layers lignified, palisade, (mesotesta not lignified); thin layer of nucellus persistent; n = 9.
1-2[list]/6. New Guinea and S.E. Australia to Fiji (map: from van Balgooy 1975; Philipson 1986b).
Age. Distinctive trimeniaceous seeds, albeit without the vascularized testa of extant taxa, have been found in Late Albian deposits some 118 m.y. old in Hokkaido, Japan (Yamada et al. 2008).
Evolution. Pollination Biology & Seed Dispersal. For pollination, see Bernhardt et al. (2003); stigmatic self-incompatibility occurs here, and both wind and insects may be involved in pollination.
Chemistry, Morphology, etc. Some plants of Trimenia papuana have inaperturate pollen, while some have polyporate pollen (Sampson 2007); the endexine is lamellate. The nucellus sometimes elongates greatly after meiosis of the megaspore mother cells, but the origin of the cells making up the massive nucellus and through the central, starch-rich cells of which the embryo sac grows (Bachelier & Friedman 2011; Friedman & Bachelier 2013) and of the megaspore mother cells themselves is unclear; are the latter initially hypodermal? Friedman and Bachelier (2013: much useful information) observed a thin, persistent layer of nucellar tissue surrounding the endosperm, but it did not contain food reserves.
See also Endress and Sampson (1983: floral development) and Philipson (1986b, 1993) for more information.