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.

PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]: Starch grains simple, amylophobic; stomata anomocytic, (cuticular waxes as parallel platelets); colleters 0; endosperm nuclear.

[[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]: nucellar cap 0.

[DIOSCOREALES + PANDANALES]: ?

Larvae, and sometimes also adults, of the Chrysomelidae-Criocerinae are scattered through this clade, being perhaps especially common on commelinids (e.g. Schmitt 1988).

For discussion on the relationships of Dioscoreales and Pandanales, see the Petrosaviales page.

DIOSCOREALES J. D. Hooker  Main Tree, Synapomorphies.

Steroidal saponins +; vascular bundles in rings; vessels also in stem and leaf; flowers or inflorescence with glandular hairs; style at most short, style branches well developed; T persistent in fruit; endotegmen tanniniferous; embryo at most short. - 5 families, 21 genera, 1037 species.

Stem-group Dioscoreales are dated to ca 124 million years before present, crown group Dioscoreales to ca 123 million years before present (Janssen & Bremer 2004).

The tepals of Narthecium ossifragum have three traces, those of Dioscoreaceae are single trace.

Nartheciaceae are rather consistently placed with Dioscoreales, albeit sometimes with only moderate support (e.g. Chase et al. 2000a; Caddick et al. 2002a; Tamura et al. 2004 [97% bootstrap, good sampling of Nartheciaceae, but otherwise only Dioscorea and Tacca and three members of Pandanales]; Janssen & Bremer 2004 [one gene, but very good sampling]; Chase et al. 2006; Givnish et al. 2006: see also Goldblatt 1995). However, Davis et al. (2004) found them to associate with Pandanales, although support was weak (<70%) and they lack the 6bp atpA deletion of many members of that clade.

Recent studies by Merckx et al. (2006) strongly suggest that the sapromyctotrophic members of Dioscoreales do not form a clade. Their study, using mitochondrial and nuclear genes and with very good sampling of these sapromyctotrophic taxa, but no outgroup to Dioscoreales, shows substantially different relationships within Dioscoreales from the tree in Caddick et al. (2002a: see /APweb/ version 7 [November] and earlier which followed the classification in Caddick et al. 2002b). However, as Merckx et al. (2006) note, the relationships found by Caddick et al. (2002a) were dominated by data from the chloroplast, and since Burmanniaceae s.l. are largely mycoheterotrophic they have much diverged plastid sequences. These mycoheterotrophic taxa have indeed caused problems. Geomitra, Thismiaceae, without any doubt, nevertheless came out with some Burmanniaceae in some analyses (Caddick et al. 2002a), while in mitochondrial genome analyses members of Burmanniaceae s.l. were in two different orders (G. Petersen et al. 2006b). In the study of the relationships of Burmanniales by Neyland (2002), Burmannioideae were well supported, Thismia was sister, but with less support, but Burmanniaceae did not link with other Dioscoreales. Furthermore, analysis of 26S rDNA sequences suggested that Corsiaceae (Liliales) were polyphyletic; Arachnitis might be sister to Thismia (Neyland & Hennigan 2003). Some genes, at least, show accelerated evolution (G. Petersen et al. 2006b; Merckx et al. 2006). The classification here follows that suggested by Merckx et al. (2006), although for realtionships within Dioscoreaceae in the sense recognized here, see Caddick et al. (2002a, b). Note that the positions of Dioscoreaceae and [Taccaceae + Thismiaceae] are reversed in the tree presented by Yokoyama et al. (2008), but with little support, while Merckx and Bidartondo (2008) suggested that Burmanniaceae s. str. might be paraphyletic, Taccaceae being embedded in them. More work is needed to elucidate the basic phylogenetic structure of Dioscoreales.

For morphology and anatomy, see Ayensu (1972), for seed coat, see Bouman (1995) and Oganezova (2000b), for pollen morphology and development see Caddick et al. (1998) and Schols et al. (2005a: Nartheciaceae and Dioscoreaceae). For much information on morphology and relationships in the order, see Caddick et al. (2000a [floral morphology and development], 2000b [general]); prolongations of the anther connective are homoplasious.

Includes Burmanniaceae, Dioscoreaceae, Nartheciaceae, Taccaceae, Thismiaceae.

Synonymy: Burmanniales Heinze, Nartheciales Reveal & Zomlefer, Taccales Dumortier, Tamales Dumortier - Dioscoreanae Reveal & Doweld - Burmanniidae Heintze

NARTHECIACEAE Bjurzon   Back to Dioscoreales

Chelidonic acid +, flavonols 0; air spaces in root cortex; fibers intermixed in phloem; (sieve tube plastids with large polygonal crystal - Narthecium); usu. druses, prismatic crystals in bundle sheath, raphides 0; cuticular wax with parallel platelets; leaves two-ranked, ensiform, isobifacial (spiral, bifacial - Aletris); bracteole 0 (+); T basally connate, A adnate basally, pollen orbicules with a circular perforation, septal nectaries +/0, G to half inferior, partly ascidiate, fusion congenital to postgenital, compitum +/0, many (unitegmic) ana-campylotropous ovules/carpel, integuments lack cuticle [check], integumentary obturator + [Aletris], (style long); seeds obliquely stacked (with appendages), shape various; tegmen flattened, persistent; endosperm helobial, [how much?, walls?]; n = (12) 13 (21, 22), 0.7-1.4 µm long; cotyledon bifacial or not, collar ?rhizoids.

4-5[list]/41: Aletris (30). N. temperate, to Venezuela and Guiana and scattered in W. Malesia (Map: incomplete, from Hultén; Jessop 1979; Fl. N. Am. 26: 2002). [Photo - Inflorescence]

• Most Nartheciaceae can be recognised by their isobifacial, equitant leaves and racemose, bracteate inflorescences with small, rather undistinguished monocot flowers that have partly free tepals that persist under the capsular fruit.

Stem-group Nartheciaceae are dated to ca 123 million years before present, the crown group diverged ca 76 million years before present (Janssen & Bremer 2004).

Metanarthecium may have abaxial prophylls. There are reports that the ovules of Narthecium may be unitegmic (Remizowa et al. 2006 for references); in general, variation in floral development is considerable (Remizowa et al. 2008).

Aletris, with its spiral and bifacial leaves, was sister to the three other genera examined (Tamura et al. 2004). Although these latter all have equitant, isobifacial leaves, that set of features cannot be an an apomorphy for the family.

The relationships of Nartheciaceae, with their rather ordinary-looking monocot flowers, have long been problematic. Thus Dahgren et al. (1985) placed them - along with representatives of Tofieldiaceae and Petrosaviaceae - in Melianthaceae (Liliales here), and Tamura (1998) placed them in Petrosaviaceae (along with genera here placed in Tofieldiaceae).

For inflorescence and flower development, see Remizowa et al. (2006a, b), leaf anatomy, see Luque Arias et al. (2006), for pollen morphology, see Merckx et al. (2008b).

[Taccaceae + Thismiaceae] [Burmanniaceae + Dioscoreaceae]: stem with endodermis; T tube broad, ovary inferior, style short, branched, stigmas ± bilobed; fruit winged; exo- and endotesta tanniniferous.

Cell walls in the endosperm are thick, but are usually not pitted.

Taccaceae + Thismiaceae: A inflexed in flower, septal nectaries 0, placentation parietal.

TACCACEAE Berchtold & J. Presl, nom. cons.   Back to Dioscoreales

Stem tubers or rhizomes, secondary thickening(?); hairs with multicellular stalk row, a head, and then another cell row; petiole bundles in ring; leaves basal, margins entire or ± deeply pinnately or palmately divided, basally somewhat sheathing; inflorescence scapose, umbellate, of groups of cincinni, bracteate, long filiform bracts among the flowers; flowers medium, T tube short, A adnate at base, connective broad, not prolonged, forming a hood with anthers on the inside, anther wall formation "dicot type", stylar canal with secretion, stigma often petaloid; fruit a berry (capsule); seed ribbed, (endotesta crystalliferous), exotegmen ± thick-walled and elongated, esp. radially; embryo short to minute; n = 15; cotyledon ?bifacial, sheath lobed.

1/12. Pantropical, esp. Malesian-Pacific (map: from Drenth 1976). [Photos - Collection.]

• Taccaceae are herbs with long-petiolate leaves and a scapose inflorescence with medium-sized, dark purple flowers that have inferior ovaries; long, filiform bracts are mixed in with the flowers and the ovary placentation is parietal.

It is unclear if the midrib is distinct or multistranded (Inamadar et al. 1983). Tacca seems to lack the distinctive vasculature of Dioscoreaceae, in which it used to be included. The cells around the raphal bundle can be thin-walled; perhaps they are attractive to animals?

For general information, see Limpricht (1928) and Kubitzki (1998b).

THISMIACEAE Agardh nom. cons.   Back to Dioscoreales

Plants mycoheterotrophic; saponins?; root hairs 0; stomata 0; leaves reduced to scales; flowers often single or in (branched) inflorescences, (monosymmetrical); T whorls often differentiated, both well developed, (apex of inner T lobes connate into a "mitre", contorted - Thismia, etc., outer T lobes then small or even 0), tube well developed, annulus +/ring of short projections/0 [Haplothismia], A inserted at apex of tube, pendulous or not, with intrastaminal lobes, (3, opposite inner T, Oxygyne), filaments variously ornamented, connective well developed, prolonged, adnate to stigma, tapetal cells uninuclear, pollen porate, many tenuinucellate ovules/carpel, placental columns often ± free, ± apical, (embryo sac bisporic), style connate early in ontogeny, stigma capitate [Thismia]/(ob)pyramidal; fruit not winged, irregularly dehiscent, P circumscissile; seeds minute, testal cells ± spiral, tegmic cells compressed; endosperm helobial (cellular - Thismia), thick-walled, with starch when young, not persisting; embryo minute, undifferentiated; seedling not easily describable [Imhof & Sainge 2008]; n = 6-9, chromosomes 1-4 µm long.

5/45: Thismia (35). Widely scattered, (sub)tropical (Map: from Jonker 1938; van Steenis & van Balgooy 1966; Maas et al. 1986; Larsen & Averyanov 2007; Dauby et al. 2008). The immediate relatives of Thismia americana, once collected near Chicago but apparently now extinct, are Antipodean (Thorne 1992). [Photo - Thismia.]

• Thismiaceae are small, echlorophyllous herbs that may be recognised by their distinctive flowers. These are usually single and terminal, the outer tepals are often rather different from the inner, there is usually an annulus surrounding the broad throat, the stamens are inflexed, or at least form a cone in the centre of the flower, and the ovary is inferior. The flowers can look like a little jelly fish, or a group of small fungi, or... Some are very small, and several new species and even genera are being described.

Merckx and Bidartondo (2008) describe what they called delayed cospeciation (the delay is 65-170 million years) of a group of Afrothismia on/with their Glomus fungal symbiont.

The stems may be endogeneous in origin (Pfeiffer 1914). The inflorescence of Afrothismia hydra seems to be cymose (Imhof & Sainge 2008), although inflorescences of species of Thismia described by Larsen and Averyanov (2007) are not so easy to interpret. Self-pollination or apomixis may be common (e.g. Maas et al. 1986), although (sapro)myophily is also a likely means of cross pollination (Woodward et al. 2007).

Information is taken from Dahlgren et al. (1985), Rübsamen (1986), Maas-van der Kamer (1999) and Tsukaya et al. (2007: chromosome number and size).

Burmanniaceae + Dioscoreaceae: ?

BURMANNIACEAE Blume, nom. cons.   Back to Dioscoreales

Plants mycoheterotrophic, (chlorophyllous - some Burmannia), roots ± fleshy, or root tubers +; saponins?; raphides 0; cuticular waxes with parallel platelets; leaves (two-ranked), usu. reduced to scales; (bracteoles lateral - Burmannia); T (moderately large), valvate, outer larger, enclosing the inner, (inner 0), tube [hypanthium] well developed, A 3, opposite inner T, thecae separated by connective, transversely dehiscent, pollen monoporate, sulcate or inaperturate, psilate, placentation ± parietal, (axile - Burmannia), many tenuinucellate ovules/carpel, (paired glands [modified septal nectaries] at apex of each placenta), style long, (branches with appendages), stigma infundibular; fruit transversely (Burmannia) or longitudinally dehiscing down the sides, or indehiscent, T persistent; seeds minute, testal cells ± spiral, tegmic cells compressed; endosperm usu helobial, thick-walled, with starch when young, not persisting, [cell formation in chalazal endosperm chamber first]; embryo minute, undifferentiated; ?seedling; n = 6 (7) 8, much and high polyploidy, chromosomes 1-2 µm long.

9 [list, inc. Thismiaceae]/95: Burmannia (63), Gymnosiphon (30). Largely tropical, esp. American (Map: from Jonker 1938; Maas et al. 1986). [Photo - Flower, Campylosiphon, Hexapterella.]

• Burmanniaceae are rather small, often echlorophyllous herbs that may be recognised by their radially symmetrical, often more or less blue flowers with an inferior ovary that is often winged. The outer tepals are rather larger than the inner and there are only three stamens, borne opposite the inner tepals.

Stem group Burmanniaceae are dated to ca 116 million years before present, crown group Burmanniaceae to ca 93 million years before present (Janssen & Bremer 2004: three genera sampled; similar dates in Merckx et al. 2008). The rather wide range of the family has largely been achieved by migration, with diversification rates being notably high in the Eocene (Merckx et al. 2008a). There has been more than one loss of chlorophyll in this clade (Merckx et al. 2006).

The root stele is di- to pentarch and may lack a pith, and although roots of Burmanniaceae are often described as lacking root hairs, as befits their close association with fungi, these are shown as occuring in Burmannia (von Guttenberg 1968). In echlorophyllous taxa vessels may be restricted to the roots, in others there are vessels in the leaves.

Information is taken from Dahlgren et al. (1985), Rübsamen (1986) and Maas-van der Kamer (1999).

DIOSCOREACEAE R. Brown, nom. cons.   Back to Dioscoreales

Climbers; flavonols +; small common and larger cauline bundles alternating, vascular bundles in two circles [not Trichopus], phloem internal to metaxylem; vessels in cauline bundles interrupted at nodes by tracheids, sieve tubes similarly interrupted; vessel elements scalariform, in petiole but not lamina; stomatal ontogeny irregular; (prophylls lateral); leaves not sheathing, conduplicate, petiolate, with midrib and reticulate fine venation, (vein endings free), petiole pulvinate at both ends; inflorescences axillary; microsporogenesis simultaneous [tetrads tetrahedral], carpels plicate, filled with secretion [Stenomeris, Trichopus?], compitum +, (outer integument ³3 cells across), micropyle bistomal, stigma wet; T persistent; seeds often winged; endotestal cells elongated, thick-walled, with crystals (0), exotegmen thickened; endosperm nuclear, embryo broad.

4[list]/870. Largely tropical. Three groups below.

1. Stenomeris

Underground stem thickened; tannin cells 0; petiole bundles in arc; gland heads two celled; T tube [hypanthium] well developed, A inserted in mouth, reflexed, microsporocytes markedly elongated; tegmen collapsed; n = ?; seedling?

1/2. W. Malesia.

Synonymy: Stenomeridaceae J. Agardh

Trichopus + Dioscorea: 2 ovules/carpel; endosperm walls thickened.

2. Trichopus

Rhizomatous, stem ± climbing; flavones +; endodermoid layer fibrous; gland heads with many transversely elongated cells in series [Trichopus s. str.]; petiole bundles in arc; petiole with basal pulvinus only (Avetra s. str. - 0); connective broad, microsporocytes markedly elongated, pollen spinulose, ovules tenuinucellate, ?micropyle; fruit dry, ± indehiscent (samara); endotesta not thickened, exotegmic cells elongated, with reticulate thickenings; endosperm ruminate, embryo minute; n = 14; germination?

1/2. Madagascar, Peninsula India, Ceylon, Peninsula Malaysia.

The pollen of Avetra s. str. is pantoporate. Trichopus s. str. lacks the distinctive vascular bundles of Avetra (the two are a single genus here) and other Dioscoreaceae, and the position of its inflorescence is not clear.

For microsporogenesis, see Caddick et al. (1998, 2000b), and for general information, see Huber (1998).

Synonymy: Avetraceae Takhtajan, Trichopodaceae Hutchinson, nom. cons.

3. Dioscorea

Tubers +; chelidonic acid +; (secondary thickening +); sieve tube plastids also with starch grains; petiole bundles in ring (not D. hemicrypta!); gland heads many celled; leaves two-ranked, also opposite, flat to curved or conduplicate, (palmately compound; midrib +; paired basal evascular processes); plant dioecious, inflorescences two or more together, (bracteoles lateral); flowers small, T free or connate, A (1) 3 (6), adnate to T or free (connate), (extrorse; prolonged connective), pollen often disulcate, compitum +, (1-4 ovules/carpel), stylar canal with secretion, stigma usually not bilobed; fruit capsular, baccate, or samaroid; ?phlobaphene, testa multi-layered, endotesta crystalliferous, exotegmen sclerotic; embryo small; n = (8), 9, 10, 12; cotyledon flattened and photosynthetic or not.

1/350-?800 (for the circumscription of Dioscorea and relationships within the genus, see Bharathan et al. 2001; Caddick et al. 2002a; Wilkin et al. 2005). Largely tropical, also warm temperate, esp. seasonal (Map: see Meusel et al. 1965; Fl. N. Am. 26: 2002; FloraBase 2004). [Photo - Inflorescence, Flower, Fruits.]

The cork is subepidermal and there may be secondary thickening in the tubers. The bundles in the stem may be arranged in a ring. The exact morphological nature of the latter is in some dispute. Lateral prophylls occur at least sometimes.

For midrib anatomy, see Edeoga and Ikem (2001).

Synonymy: Tamaceae Martynov, Tamnaceae J. Kickx f.

• Dioscoreaceae are more or less herbaceous plants with often rather small and not very brightly coloured flowers; the ovary is inferior and often ridged or winged in fruit. Many are climbers recognised by their spiral, petiolate leaves with pulvini at both ends of the petiole; the leaf base does not surround the stem. The lamina has several strong longitudinal veins and transverse secondary veins, or reticulate fine venation.

Stem group Dioscoreaceae are dated to ca 116 million years before present, crown group Dioscoreaceae to ca 80 million years before present (Janssen & Bremer 2004).

Descriptions are provided for all three genera since they have usually been placed in separate (albeit more or less closely related) families. Much more detailed information is provided by Caddick et al. (2002b).

Compound leaves in this group result from the localised activity of the marginal blastozone (Gunawardena & Dengler 2006). The flowers of Dioscorea are shown with the median member of the outer whorl in the adaxial position (Spichiger et al. 2004).

For general information, see Conran and Clifford (1985) and Huber (1998 - Dioscorea s. str. itself divided into 22 sections fully described), for anatomical information, Ayensu (1972) and Behnke (1990b: nodal anastomoses, see sieve tube interruption above), for ovules, Igersheim et al. (2001), and for pollen evolution, Schols et al. (2005b).