LIGNOPHYTA

Plant a shrub or tree; true roots +, origin endogeneous, root cap +, apex multicellular; endodermis +; shoot apical meristem multicellular; lateral meristems +, cork cambium producing cork abaxially, vascular cambium producing phloem abaxially and xylem adaxially; lamina with mean venation density 1.8 mm/mm² (to 5 mm/mm²).

EXTANT SEED PLANTS/SPERMATOPHYTA

Plant woody, 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, thus containing p-hydroxyphenyl and guaiacyl lignin units, so no Maüle reaction; root xylem exarch, cork cambium deep seated; arbuscular mycorrhizae +; shoot apical meristem interface specific plasmodesmatal network; stem with vascular tissue around central pith [eustele], vascular bundles with interfascicular tissue, ectophloic, endodermis 0, xylem endarch; 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"]; vascular bundles collateral [stem: phloem external; leaf: phloem abaxial]; stomata morphology?, pore opening controlled by abscisic acid; 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 tetrahedral, only one megaspore develops, megasporangium indehiscent; male gametophyte development first endo- then exosporic, tube developing from distal end of grain, to ca 2 mm from receptive surface to egg, gametes two, developing after pollination, with cell walls, flagellae numerous; ovules increasing considerably in size between pollination and fertilization, 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 straight, shoot and root at opposite ends [allorrhizic], white, cotyledons 2; plastid transmission maternal; ycf2 gene in inverted repeat, 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 with sieve and Strasburger/albuminous cell pairs, the two not derived from the same immediate mother cell, 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, phloem fibres +, scattered; stomata subsidiary cells not produced from the same cell that gave rise to the guard cell initials [perigenous], stomatal poles raised above pore, no outer stomatal ledges or vestibule, epidermis lignified; sclereids +, ± tracheidal transfusion tissue +; buds with scale leaves/cataphylls; plants dioecious; microsporangium with exothecium; pollen tectate, infratectum alveolate [esp. saccate pollen], endexine lamellate at maturity; ovule unitegmic, with pollen chamber formed by breakdown of nucellar cells, nucellus massive; pollination droplet +, ovules aborting unless pollination occurs, fertilisation 7 days to 4-6 months or more after pollination, pollen germinates in two or more days, tube with wall of pectose + cellulose microfibrils, branched, growing away from ovule 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 producing a sterile cell, gametes 2, released by breakdown of pollen grain wall, with >1000 cilia; female gametophyte with radially-elongated cells [alveoli] that grow centripetally, the nucleus of the female gamete being on the open face and connected to adjacent nuclei by spindle fibres; seed fleshy, testa mainly of coloured sarcoexotesta and scleromesotesta, ± vascularized, and ± degenerating endotesta, ± vascularized; first zygotic nuclear division with chromosomes of male and female gametes lining up on separate but parallel spindles, embryogenesis initially nuclear; gametophyte persists in seed; 2C genome size 25-32< pg [1 pg = 10⁹ base pairs]; two copies of LEAFY gene and three of the PHY gene, [PHYP [PHYN + PHYO]], second intron in the mitochondrial rps3 gene [group II, rps3i2].

[GINKGOALES + CYCADALES]: 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, flagellae numerous; seeds with coloured sarcoexotesta, scleromesotesta, and ± degenerating endotesta; germination cryptcotylar.

Chemistry, Morphology, etc. For stamen morphology, see Mundry and Stützel 2004b).

GINKGOALES Gorozh.  Main Tree, Synapomorphies.

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 alone [Cycadales?]; all leaves with axillary buds; 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].

Note: Possible apomorphies are now being added throughout the site; they 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 because there is very considerable homoplasy for many characters, with with variation within and between clades. Furthermore, basic information for all too many characters is very incomplete, often 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...

Phylogeny. Given the uncertainty in our knowledge of the relationships between the major seed-plant clades, direct links to them are provided here: Cycadales, flowering plants or Magnoliidae, and Pinales; for general discussion, see seed plant evolution.

Includes: Ginkgoaceae. - 1 family/1 genus/1 species [rather redundant].

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

GINKGOACEAE Engler Back to Ginkgoales

Plant with lignotubers; resin, mucilage +; cork cambium subhypodermal; short shoots + [bearing sporophores/strobili], wood there manoxylic; sclereids +; leaves deciduous; (cotyledons 3); n = 12.

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

• Ginkgoaceae are large deciduous trees with stout and conspicuous short shoots; the leaves have dichotomous venation.

Evolution. Divergence & Distribution. 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 Tertiary fossil history of Ginkgo, see Manchester et al. (2009).

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. 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.

The integument is initiated in two places, but soon becomes 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 Crane (2013: general), Friedman (1987: male gametophyte development), Dute (1994: torus:margo pits), Soma (1997: female gametophyte and embryogeny), the papers in Hori et al. (1997) in general, Mundry and Stützel (2004b: stamen and leaf development), Douglas et al. (2007: ovule), Dogra (1992) and Wang et al. (2011), both embryology, Rudall et al. (2012: stomatal development), and the Gymnosperm Database (general).