EMBRYOPSIDA Pirani & Prado

Gametophyte dominant, independent, multicellular, thalloid, with single-celled apical meristem, showing gravitropism; rhizoids +, unicellular; acquisition of phenylalanine lysase [PAL], phenylpropanoid metabolism [lignans +, flavonoids + (absorbtion of UV radiation)], xyloglucans +; plant [protoplasm dessication tolerant], ectohydrous [free water outside plant physiologically important]; 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, initially laid down in association 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.

STOMATOPHYTES

Abscisic acid, ?D-methionine +; sporangium with tapetal layer, columella + [developing from endothecial cells], seta developing from basal meristem [between epibasal and hypobasal 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.

POLYSPORANGIOPHYTA†

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; lignins +; vascular tissue +sieve cells + [nucleus degenerating], tracheids +, in both protoxylem and metaxylem, plant endohydrous [physiologically important free water inside plant]; 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]; G-type 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.

LIGNOPHYTA†

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].

SEED PLANTS†

Plants heterosporous; megasporangium surrounded by cupule [i.e. 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); primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins particularly with guaiacyl and p-hydroxyphenyl [G + H] units [sinapyl units uncommon, 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.; axillary buds exogenous, (none; not associated with all leaves); 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], primexine + [involved in exine pattern formation and deposition of sporopollenin from tapetum], exine and intine homogeneous; megasporangium indehiscent; ovules unitegmic, parietal tissue 2+ cells across, megaspore tetrad linear, functional megaspore single, chalazal, sporopollenin 0; gametophytes dependent on sporophyte, apical cell 0, rhizoids 0; male gametophyte development initially endosporic, tube developing from distal end of grain, gametes two, developing after pollination, with cell walls; female gametophyte 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.

EXTANT GYMNOSPERMS / PINOPHYTA / ACROGYMNOSPERMAE

Biflavonoids +; cuticle wax tubules with nonacosan-10-ol; ferulic acid ester-linked to primary unlignified cell walls; phloem sieve area with small pores generally less than 0.8 µm across that have cytoplasm and E.R., joining to form a median cavity in the region of the middle lamella, Strasburger/albuminous cells associated with sieve tubes [the two not derived from the same immediate mother cell], phloem fibres +; sclereids +, ± tracheidal transfusion tissue +; stomatal poles raised above pore, no outer stomatal ledges or vestibule, epidermis lignified; buds perulate/wiith cataphylls; lamina development marginal; plants dioecious; microsporangium with exothecium; pollen tectate, infratectum alveolate [esp. saccate pollen], endexine lamellate at maturity, esp. intine with callose; ovule unitegmic, with pollen chamber formed by breakdown of nucellar cells, nucellus massive; ovules increasing considerably in size between pollination and fertilization, but aborting unless pollination occurs; ovule with pollination droplet; pollen grain lands on ovule, germinates in two or more days, tube with wall of pectose + cellulose microfibrils, branched, growing at up to 10(-20) µm/hour, haustorial, breaks down sporophytic cells; male gametophyte of two prothallial cells, a tube cell, and an antheridial cell, the latter producing a sterile cell and 2 gametes; male gametes released by breakdown of pollen grain wall, with >1000 cilia, basal body 800-900 nm long; fertilization 7 days to 12 months or more after pollination, to ca 2 mm from receptive surface to egg; female gametophyte initially with central vacuole and peripheral nuclei plus cytoplasm, cellularization/alveolarization by centripetal formation of anticlinal walls, the inner periclinal face open, with a single nucleus connected to adjacent nuclei by spindle fibres; seeds "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; testa mainly of coloured sarcoexotesta, scleromesotesta, and ± degenerating endotesta; first zygotic nuclear division with chromosomes of male and female gametes lining up on separate but parallel spindles, embryogenesis initially nuclear, embryo ± chlorophyllous; gametophyte persists in seed; plastid and mitochondrial transmission paternal; nuclear genome size 8-32(-76) pg [1 pg = 109 base pairs]; two copies of LEAFY gene [LEAFY, NEEDLY] and three of the PHY gene, [PHYP [PHYN + PHYO]], second intron in the mitochondrial rps3 gene [group II, rps3i2].

[Ginkgoales + Cycadales]: mucilage +; phloem with scattered fibres; cataphylls +; double leaf trace; lamina/leaflet midrib 0; plants dioecious; pollen tube branched, growing away from the ovule; spermatogenous cells delimited by circular anticlinal wall, zooidogamy, male gametes with cell wall, released from the swollen proximal part of the tube, cilia numerous; seeds with coloured sarcoexotesta, scleromesotesta, and ± degenerating endotesta; germination hypogeal, cryptocotylar.

Age. Estimates for the age of this node are (257.7-)163.3(-75.9) m.y. in Zhang et al. (2014) but only ca 107 m.y.a. in Z. Wu et al. (2014).

GINKGOALES Gorozh.  Main Tree.

VAM present; biflavones, non-hydrolysable tannins +; tree branched; compression wood +; nodes 1:2, venation dichotomising, open; wood pycnoxylic; tracheid side wall pits with torus:margo construction, bordered; phloem with scattered fibres; double leaf trace +; all leaves with axillary buds; lamina lacking a midrib, venation dichotomous; microsporangiophore/filament simple with terminal microsporangia; microsporangia 2/microsporophyll, abaxial, pendulous, dehiscing by the action of the hypodermis [endothecium]; exine thin [2³ µm thick]; megasporophyll single, ovules 2(-4) together, terminal, erect, nucellar beak +, with basal collar; generative cell delimited by circular anticlinal wall, pollen tube penetrating between sporophytic cells, growth non-destructive, wall with ß-(1,3)(1,4)-glucan; seed fleshy, inner fleshy layer alone vascularized; germination cryptocotylar; one duplication in the PHYO clade. - 1 family, 1 genus, 1 species [all rather redundant].

Age. Ginkgoales were almost world-wide in distribution and included several genera in the Mesozoic. They have a possible origin from Palaezoic pteridosperms, perhaps in the Upper Carboniferous (Thomas & Spicer 1987; Zhou 1997). The morphology of these early Ginkgo-like plants is uncertain, but the ovules may have been more numerous, very differently arranged and some at least were inverted (and/or platyspermic). Ginkgo-like leaves are known from the Permian onwards (see Zhou & Zhang 2003). For the early Caenozoic fossil history of Ginkgo, see Manchester et al. (2009).

The clade [Ginkgoales + Pinales] was estimated to be around 84.35 m.y.o. (!: Naumann et al. 2013) or over three times as old, (327-)304(-283) m.y.o. (Clarke et al. 2011).

Note: (....) denotes a feature common in the clade, exact status uncertain, [....] includes explanatory material. 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).

Phylogeny. For discussion on the relationships of Ginkgoales, see above. Given the uncertainty in our knowledge of the relationships between the major seed-plant clades, direct links to Cycadales, Gnetales, flowering plants, and Pinales are provided here.

Includes: Ginkgoaceae.

Synonymy: Ginkgoidae Engler - Ginkgoopsida Engler - Ginkgoophytina Reveal - Ginkgoophyta Bessey

GINKGOACEAE Engler Back to Ginkgoales

Ginkgoaceae

Plant with lignotubers; resin, mucilage +; cork cambium subhypodermal; sclereids +; long and short shoots alternating along the axis, the latter also axillary, bearing sporophores/strobili, wood there manoxylic; stomata ± stephanocytic s. str.; leaves deciduous; (cotyledons 3); n = 12.

1/1: Ginkgo biloba. E. China, but perhaps now only in cultivation. [Photo - Microsporangia, Ovules, and Seeds.]

Evolution. Divergence & Distribution. For the phylogeography of Ginkgo biloba, see Gong et al. (2008). Ecological evidence suggested to C. Q. Tang et al. (2012) that wild populations still persist.

Genes & Genomes. For the chloroplast genome, with its somewhat contracted inverted repeat, see Lin et al. (2012). Dioecy may be associated with chromosomal differentiation (female xx, male xy), but c.f. Hizume (1997).

Chemistry, Morphology, etc. For stem growth and anatomy, see Little et al. (2013 and references). The leaf is innervated by two leaf traces that originate from independent sympodia; there are a very few anastomoses between the veins in the blade. Rudall et al. (2012) discussed stomatal development; some authors have suggested that the cells surrounding the stomata have small papillae ± overarching the guard cells.

The integument is initiated in two places, but the two parts soon become confluent. The chalazal cell of the linear tetrad develops to form the female gametophyte. The nuclei of the female gametophyte have the same DNA content as diploid cells (Friedman & Gifford 1997).

For additional information, see the papers in Hori et al. (1997) and Crane (2013) both general, Dute (1994: torus:margo pits), Bonacorsi and Seago (2014: root anatomy), Dörken (2014: vegetative anatomy and morphology), Friedman (1987: male gametophyte development), Soma (1997: female gametophyte and embryogeny), Mundry and Stützel (2004b: stamen and leaf development), Douglas et al. (2007: ovule), Dogra (1992) and Wang et al. (2011), both embryology), and the Gymnosperm Database (general).