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.

ROSID I/FABIDAE  Back to Main Tree

Endosperm scanty.

ZYGOPHYLLALES Chalk. [not in A.P.G.]  Main Tree, Synapomorphies.

Harman alkaloids, diversity of linans and neolignans +; cork cambium deep cortical or pericyclic (superficial); vessel elements with simple perforation plates; rays (predominantly) uniseriate; tension wood?; (stomatal orientation transverse); (pollen colpate), style +; seeds ± exotestal; endosperm 0; chloroplast infA gene +. - 2 families, 27 genera, 305 species.

For harman alkaloids, see Kubitzki (2006a); for lignans and neolignans, see Simpson (2006) and Sheahan (2006). Carlquist (2005b) lists several features of wood anatomy that may be synapomorphies for the group.

Wikström et al. (2001) suggest an age for Zygophyllales of some 101-95 my, and separation of the two families some 70-64 million years before present. Mycorrhizae may be absent from the whole clade.

The inclusion of Krameriaceae in Zygophyllaceae is optional, although the two do not have much in common; see A.P.G. II (2003). Zygophyllaceae are sister to Krameriaceae in Soltis et al. (1998) and Savolainen et al. (2000a), however, relationships of Zygophyllales are unclear. Hilu et al. (2003) find Larrea (Zygophyllaceae) to be weakly associated with Fabaceae, the only member of Fabales included in their rbcL analysis; they note that the possession of anthroquinones is a possible synapomorphy between Zygophyllaceae and the N-fixing clade (see also Sheahan & Chase 2000).

Includes Krameriaceae, Zygophyllaceae.

Synonymy: Balanitales C. Y. Wu - Zygophyllanae Doweld

KRAMERIACEAE Dumortier, nom. cons.   Back to Zygophyllales

Hemiparasitic shrubs to herbs; hairs unicellular, thin-walled; wood fluorescence?; nodes 1:1; petiole bundle (deeply) arcuate; stomata usu. paracytic; cuticle waxes ± ribbon-like platelets; leaves spiral (trifoliolate), entire, stipules 0; inflorescence racemose, or flowers solitary, pedicels articulated; flower monosymmetric, K (4) 5, petaloid internally, median member abaxial, larger than the others, (2) 3 adaxial C clawed, ± connate, 2 abaxial smaller, not clawed, glandular [often secreting lipid], A (3) 4, (adnate to adaxial C), anthers porose, endothecial cells with thickening parallel to long axis of cells, G [2], adaxial member much reduced, 2 collateral pendulous ovules/carpel, outer integument ca 6 cells and inner integument 4-5 cells across, micropyle endostomal, style long, stigma small, recessed; fruit nut-like, with retrorsely barbed spines; seed 1, exotestal cells enlarged, tanniniferous, tegmen to 7 cells thick, largely disappearing; endosperm development?, cotyledons large, cordate/auriculate; n = 6, chromosomes 10-24.6 µm long; seedlings without root hairs.

1[list]/18. S.W. U.S.A. to Chile, the West Indies (Map: from Simpson et al. 2004). [Photo - Flower © Jim Manhart, Fruit © Dan Nickrent]

• Krameriaceae may be recognised by their small, spiral, often elliptic, entire leaves and their distinctive, rather pea-like flowers. These are inverted, with the odd petal adaxial, and have four or five large elliptic sepals that are petaloid internally; the three strongly clawed adaxial petals are more or less connate by their bases and the usually four fertile stamens are also adaxial. The one-seeded fruits have retrorsely-barbed spines.

Bees (Centris) collect oil from the flowers on their legs from the paired, modified, abaxial petals; the latter have epithelial elaiophores (Vogel 1974; Simpson et al. 1977).

There are no vessels in the leaves, and the traces to the sepals, petals and stamens in the flower are all separate. The roots have a red phlobaphene pigment. Simpson (1982, 2006) discussed the long controversy over the orientation of the flower, however, the flowers do appear to be inverted (cf. also Milby 1971, see Fig. 73 in Simpson 2006).

For further details, see Leinfellner (1971: ovary), Verkeke (1985: ovule and seed), Simpson (1989) and Carlquist (2005b: wood anatomy); Simpson et al. (2004) provide a phylogeny of the family and Simpson (2006), and The Parasitic Plant Collection and also Heide-Jørgensen (2008) give much general information.

ZYGOPHYLLACEAE R. Brown, nom. cons.   Back to Zygophyllales

Trees to herbs (thorny); mycorrhizae absent; (C₄ photosynthesis), anthroquinones +, ellagic acid 0, tannins 0 [Zygophyllum]; wood often fluorescing; storying +; pits vestured; nodes often swollen or jointed, (with split laterals); cortical strands of fibers and sclereids +; petiole bundle annular, with flange bundles; stomata anomocytic; leaves opposite (spiral), (odd-) even-pinnate (2, 3-foliolate), ptyxis flat or, (2ndary veins ± palmate), toothed, stipules (spinescent) cauline, or 1, interpetiolar (0); A obdiplostemonous, or equal and opposite to the petals, pollen variable, nectary as basal scales adaxial to A, or annular disc, G [(2-)5], opposite petals, 1-10 ovules/carpel, micropyle variable, endothelium +, style short to long, stigma punctate, or as commissural ridges down style, dry or wet; fruit a loculicidal or septicidal capsule (dry indehiscent; schizocarp; drupe; berry); (seed arillate), exotesta palisade or not, endotesta crystalliferous, lignified or not, endotegmic cells periclinally elongated, lignified; (endosperm +), embryo green.

22[list]/285 - 5 groups below. Dry and warm temperate, also tropical (Map: from Beier et al. 2004, esp. Brummitt 2007.)[Photo - Flower, Fruit.]

1. Morkillioideae (Engler) Rose & J. H. Painter

3/4. Mexico, Baja California.

2. Tribuloideae (Reichenbach) D. H. Porter

6/63: Tribulus (25), Kallstroemia (17). World-wide.

The pollen may be polyporate.

Balanites is very different from other Zygophyllaceae in both floral and vegetative features. It is a thorny shrub or tree with bitter bark, the petiole anatomy is complex, and the stomata on the stem are transverse to the axis. The leaves are spiral and 2-foliolate. There is 1 pendulous ovule per carpel with a zig-zag micropyle. The fruit is a drupe with a single seed and no endosperm (Sheahan & Cutler 1993; see also Parameswaran & Conrad 1982; Sands 2001 for a monograph). Balanites also differs from other Zygophyllaceae in seed anatomy (Boesewinkel 1994). However, it is to be included in Tribuloideae for the time being, at least (Sheahan & Chase 1996, 2000). Howard (1970) found no stipules in Balanites, but they are present, if minute.

Synonymy: Balanitaceae M. Roemer nom. cons., Tribulaceae Trautvetter

3. Seetzenioideae Sheahan & Chase

Prostrate herbs; C 0, A 5, opposite?, 1 ovule/carpel, endothelium 0, styles 5; fruit septicidal, with pyrenes; endosperm +.

1/1: Seetzenia lanata. S. Africa, and N. Africa to Afghanistan.

4. Larreoideae Sheahan & Chase

Stamens often with scales, ovary stipitate or not; fruit capsular, winged or not, 1 seed/loculus; endosperm +.

7/30: Bulnesia (8). S.W. U.S.A. and Mexico to South America.

In at least some species of Larrea chloroplasts are inherited paternally (Yang et al. 2000).

5. Zygophylloideae

4/137: Zygophyllum (100). Mostly drier areas of the Old World, also S.W. U. S. A. and Chile.

For relationships, morphology, and a reclassification, see Beier et al. (2003). The style of Zygophyllum is more or less gynobasic.

• Zygophyllaceae are a variable group growing in more or less arid and saline conditions almost worldwide. They are herbs to trees often with compound usually stipulate and opposite leaves that lack a terminal leaflet; the nodes tend to be swollen. The flowers have all parts free apart from the carpels; there are usually ten stamens that often have scales at the base. Some aspects of floral morphology, e.g. obdiplostemony, the stigma, are reminiscent of Geraniales.

Caterpillars of Lycaeninae are quite commonly found on plants of this family (Fielder 1995). Larrea tridentat, the creosote bush, is an important shrub of the deserts of S.W. North Ammerica. Fourteen species of a clade of the cecidomyiid gall former, Asphondylia, have diversified on different parts of the plant of the one species.

Guaiacum has very hard, self-lubricating wood and was used to make bearings.

There is considerable variation in ovule type. Viscainoa has simple, spiral, trilacunar leaves and two epitropous ovules/carpel.

Phylogenetic relationships within the family are fairly well resolved; Sheahan and Chase (1996, also 2000), and can be summarised as [Morkellioideae + Tribuloideae] [Seetzenioideae [Larreoideae + Zygophylloideae]], however, there do not seem to be good characters for the groups. For relationships between Larrea and relatives, see Lia et al. (2001). Some genera that used to be included in Zygophyllaceae are now in Nitrariaceae (Sapindales, rosid II).

For floral orientation, see Eckert (1966), for nodal anatomy, see Howard (1970), for chemistry, see Hegnauer (1973, 1990), for a general account, see Sheahan (2006), for C₄ photosynthesis, see Muhaidat et al. (2007), and for character evolution, etc., in the southern African representatives, see Bellstedt et al. (2008).