EXTANT SEED PLANTS

Plant woody, evergreen; nicotinic acid metabolised to trigonelline; primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins rich in guaiacyl units; true roots present, xylem exarch, branching endogenous; arbuscular mycorrhizae +; shoot apical meristem complex; stem with ectophloic eustele, endodermis 0, xylem endarch, branching exogenous; vascular tissue in t.s. discontinuous by interfascicular regions; vascular cambium + [xylem ("wood") differentiating internally, phloem externally]; wood homoxylous, tracheids +; tracheid/tracheid pits circular, bordered; sieve tube/cell plastids with starch grains; phloem fibers +; stem cork cambium superficial, root cork cambium deep seated; nodes ?; stomata ?; leaf vascular bundles collateral; leaves spiral, simple, axillary buds?, prophylls [including bracteoles] two, lateral, veins -5(-8) mm/mm²; plant heterosporous, sporangia eusporangiate, on sporophylls, sporophylls aggregated in indeterminate cones/strobili; true pollen [microspores] +, grains mono[ana]sulcate, exine and intine homogeneous, ovules unitegmic, crassinucellate, 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, with cell walls, with many flagellae; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large", first cell wall of zygote transverse, embryo straight, endoscopic [suspensor +], short-minute, with morphological dormancy, white, cotyledons 2; plastid transmission maternal; two copies of LEAFY gene, PHY gene duplication, mitochondrial nad1 intron 2 and coxIIi3 intron present.

MAGNOLIOPHYTA

Plant woody, evergreen; lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, cyanogenesis via tyrosine pathway [ANITA grade?], lignins derived from both coniferyl and sinapyl alcohols, containing syringaldehyde [in positive Maüle reaction, syringyl:guaiacyl ratio less 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; stem with 2-layered tunica-corpus construction; wood fibers and wood parenchyma +; reaction wood ?, with gelatinous fibres; starch grains simple; primary cell wall mostly with pectic polysaccharides; tracheids +; sieve tubes eunucleate, with sieve plate, companion cells from same mother cell that gave rise to the tube, the sieve tube with P-proteins; nodes unilacunar; stomata with ends of guard cells level with aperture, paracytic; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, vein endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, development in general centripetal, numbers unstable, P not differentiated, outer members not enclosing the rest of the bud, smaller than inner members, A many, with a single trace, introrse, filaments stout, anther ± embedded in the filament, tetrasporangiate, dithecal, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally by action of hypodermal endothecium, endothecial cells elongated at right angles to long axis of anther, tapetum glandular, binucleate, microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing, pollen subspherical, binucleate at dispersal, trinucleate eventually, tectum continuous or microperforate, exine columellar, endexine thin, compact, lamellate only in the apertural regions, pollen germinating in less than 3 hours, tube elongated, growing at 80-600 µm/hour, with callose plugs and callose-based walls, penetrating between cells, siphonogamy, penetration of ovules within ca 18 hours, distance to first ovule 1.1.-2.1 mm, nectary 0, G free, several, ascidiate, with postgenital occlusion by secretion, few [?1] ovules/carpel, ovules marginal, anatropous, bitegmic, [outer integument often largely subdermal in origin, inner integument dermal], micropyle endostomal, integuments 2-3 cells thick, megasporocyte single, megaspore lacking sporopollenin and cuticle, chalazal, female gametophyte ?type, stylulus short, hollow, stigma ± decurrent, wet [secretory]; P deciduous in fruit; seed exotestal; double fertilisation +, endosperm ?diploid, cellular [first division oblique, micropylar end initially with a single large cell, chalazal end more actively dividing], copious, oily and/or proteinaceous, embryo cellular ab initio; germination hypogeal, seedlings/young plants sympodial; Arabidopsis-type telomeres [(TTTAGGG)_n]; whole genome duplication, 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 PHYA/PHYC gene pairs.

Possible apomorphies are in bold. Note that the actual level to which many of these features, particularly the more cryptic ones, should be assigned is unclear, because some taxa basal to the [magnoliid + monocot + eudicot] group have been surprisingly little studied. Furthermore, details of relationships among gymnosperms will affect the level at which some of these characters are pegged.

NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessels +, elements with scalariform perforation plates; nucleus of egg cell sister to one of the polar nuclei; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

CORE EUDICOTS   Back to Main Tree

Ellagic and gallic acids common; micropyle?; PI-dB motif +, small deletion in the 18S ribosomal DNA common.

Stem group Gunnerales date from 115 to 112 million years before present, the date of divergence of the core eudicot clade (Anderson et al. 2005); the clade that includes both groups has stem ages of 120-116 million years before present with its divergence beginning 116-115 million years before present.

Whether or not the rps2 and rps11 genes occur in Gunnerales is apparently unknown, but the first is absent in Buxales and Trochodendrales and the second in Buxales alone (Adams et al. 2002b); they are probably lost slightly lower down on the tree (as are benzylisoquinoline alkaloids).

This clade is strongly supported, e.g. Chase et al. (1993), D. Soltis et al. (1997, 1999, 2003a), Hoot et al. (1998), and Nandi et al. (1998), and Zhu et al. (2007), although indistinguishable from other core eudicots in (e.g.) P. Soltis et al. (1999). In early studies, Gunneraceae were an early branching clade within the core eudicots, although their exact position was unclear (e.g. Chase et al. 1993; Morgan & Soltis 1993), but quite strong support for a position sister to the rest was provided by Senters et al. (2000: Gunneraceae alone sampled), rather weaker support by Hilu et al. (2001). A four-gene analysis provides strong support for this position (D. Soltis et al. 2003a).

The apparently plesiomorphic floral morphology of Gunnerales is more like that of Buxales, etc., i.e., of taxa on more basal branches in the eudicots, and is not very like that of other core eudicots (e.g. D. Soltis et al. 2003a; Doust & Stevens 2005; Kubitzki 2006a). However, note that chemically they seem similar to core eudicots, e.g. they have ellagic acid (e.g. Soltis et al. 2005b), also, they have the euAP3 gene (see above), and general molecular data link them closely with core eudicots - although some perhaps important gene duplications may have occured somewhat earlier (see Trochodendrales page). Wanntorp and Ronse De Craene (2005) and Ronse De Craene and Wanntorp (2006) note that the morphology of Gunnerales flowers cannot be directly related to that of the pentamerous core eudicots, the floral morphology of the former being shaped by the exigencies of wind pollination. Wanntorp and Ronse De Craene (2005) also note that three successive floral whorls may be opposite each other, a feature e.g. of some Ranunculales like Berberidaceae, Sabiales, etc., but not of core eudicots. Indeed, the flowers cannot be considered as being derived from those of other core eudicots given our current knowledge of floral morphology and development.

Gunnerales were excluded from the core eudicots in earlier versions of this site (pre Version 8; cf. A.P.G. I and II 1999, 2003) because of their apparently largely plesiomorphic floral morphology. However, in the interests of consistency their limits have been adjusted to conform with those generally used.

GUNNERALES Reveal   Main Tree, Synapomorphies.

Ellagic acid +; vessel elements?; sieve tube plastids with protein crystalloids and starch; pith with sclerenchymatous diagrams; leaves with toothed margins, 2ndary veins palmate; plants dioecious, flowers small; P 0, stigma at most weakly secretory; seed coat?

Stem group Gunnerales date from 115 to 112 million years before present, the dates for the crown group members being 90-55 million years before present (Anderson et al. 2005).

The plesiomorphic condition for the order may be to have some kind of perianth.

This is a rather surprising group. Gunneraceae and Myrothamnaceae look rather different; one is an often gigantic mesophytic herb, the other a resurrection shrub of arid habitats. In the former, hydathodes are well developed and mucilage or possibly resinous lacquer is secreted, in the latter, hydathodes are poorly developed and the plant secretes resin. They do both have flowers without much of a perianth, but details of pollen (e.g. cf. Zavada & Dilcher 1986; Wanntorp et al. 2004), etc., differ. So although there is an option of including Myrothamnaceae in Gunneraceae in A.P.G. II (2003), both being small and monogeneric families, it seems best to keep them separate (see Wilkinson 2000 for a table of differences).

Includes Gunneraceae, Myrothamnaceae. 2 families, 2 genera, ca 45 species.

Synonymy: Myrothamnales Reveal - Myrothamnanae Takhtajan

GUNNERACEAE Meisner, nom. cons.   Back to Gunnerales

Perennial (annual) rhizomatous or stoloniferous herbs; Nostoc colonies in stem and root; cork ?; vessel elements with simple or few-barred scalariform perforation plates [stems] or scalariform, bars to ca 150 [stolons]; axis polystelic [stem] or vascular cylinder [stolons]; nodes multilacunar; stem with endodermis, also low glandular areas; ; petiole anatomy complex; cataphylls common; leaves spiral [opposite scales on stolons], colleters +; inflorescence usu. branched-racemose, (plant polygamous), bracteoles 0; P 2 (3), valvate, staminate flowers: (P 4, 0), A 1-2, pollen semitectate-reticulate, pistillodes +; carpellate flowers: staminodes +, G [2], inferior, transverse and alternate with P, uni(bi)locular, 1 (2) apical ovules, inner integument ca 4 cells across, micropyle endostomal, embryo sac tetrasporic 16-celled [Peperomia-type], stigmas dry; fruit drupaceous (nut); seed coat?; endosperm with some starch; n = 17.

1[list]/40-50. Circum S. Pacific, Africa and Madagascar (Map: see van Balgooy 1975; Wanntorp & Wanntorp 2003). [Photo - Leaf, Inflorescence]

• Gunneraceae are sometimes huge herbs that can be recognised by their spiral leaves the blades of which are toothed and have palmate venation that is very prominent on the lower surface, their often rather stipule-like "scale leaves", and their relatively large and branched inflorescences bearing many small, inconspicuous flowers; the ovary is inferior and bicarpellate.

All taxa have an association with the cyanobacterium, Nostoc. Glands on the stem found immediately below the leaves secrete mucilage, and Nostoc enters the plant here; Johansson and Bergman (1994, and references) describe details of the establishment of this association and Söderbäck and Bergman (1993) details of the physiology of the two partners. The pollen is distinctive and is known from the Early Cretaceous onwards (Wanntorp et al. 2004b) in all four continents of the Southern Hemisphere, as well as North America and possibly also Asia.

There are stipule-like structures on the stem of many species (but this is not an apomorphy for the family) that are interpreted as being cataphylls by Wanntorp et al. (2003); these are at least sometimes opposite and may be prophylls. They range in shape from being suboblong and entire to deeply laciniate with linear lobes. The lamina varies from 7 mm to 3 m across, and the teeth have a glandular apex that broadens distally; two higher order veins are also involved. The difference in anatomy between stems and stolons is striking; the roots are triarch to polyarch (Wilkinson 2000). Although G. herteri, sister to the rest of the genus, has normal stem anatomy, it is an annual and its anatomy is conceivably derived. The difference in size, etc., between the inner and outer tepals is such that they are sometimes described as sepals and petals (e.g. Wanntorp & Ronse De Craene 2005; Ronse de Craene & Wanntorp 2006). The rather uncommon perfect flowers then have two median sepals, two lateral petals, two stamens opposite the petals, and two carpels opposite the petals (Ronse de Craene & Wanntorp 2006).

In the past Gunneraceae have often been associated with Haloragaceae, also with an inferior ovary and reduced flowers, but in the latter the stamens are as many as the sepals, and opposite them, the gynoecium is multilocular, with one ovule/loculus, etc. - see Saxifragales. Gunneraceae were included in Saxifraganae - Rosidae by Takhtajan (1997). Recently Fuller and Hickey (2005), examining details of leaf architecture, etc., suggested that Gunneraceae were best associated with the herbaceous Saxifragaceae, but this is probably because of habit/habitat-associated parallelisms.

Much information is taken from Wilkinson (1998: anatomy); for ovules, etc., see Schnegg (1902), for a phylogeny of the genus, see Wanntorp et al. (2001) and Wanntorp (2006: summary), for pollen, Wanntorp et al. (2004a), and for floral morphology and development see Rutishauser et al. (2004) and Wanntorp and Ronse De Craene (2005) and Ronse De Craene and Wanntorp (2006); Wilkinson and Wanntorp (2006) summarize what is known about the family.

MYROTHAMNACEAE Niedenzu, nom. cons.   Back to Gunnerales

Aromatic-resinous shrubs; essential oils, gallotannins, myricetin, dihydro/chalcones +; cork?; vessel elements with reticulate perforations; nodes split-lateral; petiole bundle arcuate; individual epidermal cells resiniferous; plant glabrous; leaves opposite, basally forming a sheath, plicate, 2ndary veins palmate-flabellate, stipules 2, small, persisting on the petiolar sheath; spikes bracteate, with terminal flowers; staminate flowers: A 3-4, or (3-)4(-8) and connate, anthers valvate basally, connective produced, pollen in tetrads, intectate, with clavate projections themselves papillate, pistillode 0; carpellate flowers: staminodes 0, G 3-4, only basally connate, with 5 vascular bundles and surface oil cells, the odd member abaxial, many ovules/carpel, embryo sac bisporic 8-celled [Allium-type], micropyle bistomal, styles short, recurved, stigma decurrent, in two crests; fruit follicular (and septicidal); exotestal cells with somewhat thickened outer walls; endosperm development?; n = 10.

1[list]/2. Africa and Madagascar (Map: from Puff 1978b). [Photos - Collection]

• Myrothamnaceae are resurrection plants; the leaves may appear to dry out, but they regain turgor, etc., when conditions improve. They are vegetatively very distinctive aromatic shrubs; the leaves are opposite and have a long, common sheath on which there are four persistent stipular points, and the blades have palmate secondary veins and toothed margins.

The stems are narrowly winged and there is no axial parenchyma. There are four veins in the leaf sheaths - two bundles going directly to the midrib, and two commissural veins (Grundell 1933). Since carpellate flowers lack perianth or staminodes, it is not clear if the ovary is inferior. When flowers are terminal - on the main or lateral axes - there are four "Hochblätter" as well as bracts and bracteoles, and the four carpels are opposite the former (Jäger-Zürn 1966) which might even be interpreted as tepals (Wanntorp and Ronse De Craene 2005); see also Puff (1978a, 1978b). The carpellate flowers have been described as being zygomorphic (Moore et al. 2007).

Myrothamnaceae were included in Hamamelididae by Takhtajan (1997).

For information, see Kubitzki (1993b: general) and Moore et al. (2007: physiology, which shows surprising infraspecific variation).