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 + [nucleus degenerating], tracheids +, in both protoxylem and metaxylem; endodermis +; root xylem exarch [development centripetal]; stem with an apical cell; leaves spiral, blades 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 apex multicellular, 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; shoot apical meristem multicellular; lateral meristems axillary; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
EXTANT SEED PLANTS/SPERMATOPHYTA
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins derived from (some) sinapyl and particularly coniferyl alcohols [hence with p-hydroxyphenyl and guaiacyl lignin units, so no Maüle reaction]; root 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, 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; pollen grains landing on ovule; 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.
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 +, scattered; stomatal poles raised above pore, no outer stomatal ledges or vestibule, epidermis lignified; sclereids +, ± tracheidal transfusion tissue +; buds perulate/wiith cataphylls; lamina development marginal; 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; ovules increasing considerably in size between pollination and fertilization, but aborting unless pollination occurs; pollination droplet +; 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 and 2 gametes; fertilization 7 days to 4-6 months or more after pollination, gametes released by breakdown of pollen grain wall, with >1000 cilia; to ca 2 mm from receptive surface to egg, 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; seeds fleshy, "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; 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 [LEAFY, NEEDLY] 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.
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].
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 Tertiary fossil history of Ginkgo, see Manchester et al. (2009).
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...
Phylogeny. Given the uncertainty in our knowledge of the relationships between the major seed-plant clades, direct links to them are provided here: Cycadales, Gnetales, flowering plants, 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; 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.
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 - some authors suggest that the cells surrounding the stomata have small papillae ± overarching the guard cells), and the Gymnosperm Database (general).