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.

MAGNOLIOPHYTA

Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], S [syringyl] lignin units common, positive Maüle reaction [syringyl:guaiacyl ratio more 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, exodermis +; shoot apex with tunica-corpus construction, tunica 2-layered; reaction wood ?, associated gelatinous fibres [g-fibres] with innermost layer of secondary cell wall rich in cellulose and poor in lignin; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, wood parenchyma +; sieve tubes enucleate, sieve plate with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, cytoplasm not occluding pores of sieve plate, companion cell and sieve tube from same mother cell; sugar transport in phloem passive; nodes unilacunar [1:?]; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, secondary veins pinnate, overall growth ± diffuse, venation hierarchical, fine venation reticulate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic, parts spiral [esp. the A], free, numbers unstable, development in general centripetal; P not sharply differentiated, with a single trace, outer members not enclosing the rest of the bud, often smaller than inner members; A many, filament not sharply distinguished from anther, stout, broad, with a single trace, anther introrse, tetrasporangiate, sporangia in two groups of two [dithecal], ± embedded in the filament, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally, endothecium +, endothecial cells elongated at right angles to long axis of anther; tapetum glandular, cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellar, endexine thin, compact, lamellate only in the apertural regions; nectary 0; G superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus short, hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry [not secretory]; ovules few [?1]/carpel, marginal, anatropous, bitegmic, micropyle endostomal, outer integument 2-3 cells across, often largely subdermal in origin, inner integument 2-3 cells across, often dermal in origin, parietal tissue 1-3 cells across [crassinucellate], nucellar cap?; megasporocyte single, hypodermal, megaspore tetrad linear, functional megaspore chalazal, lacking sporopollenin and cuticle; female gametophyte four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; ovule not increasing in size between pollination and fertilization; pollen binucleate at dispersal, male gametophyte trinucleate, germinating in less than 3 hours, pollination siphonogamous, tube elongated, growing between cells, growth rate 20-20,000 µm/hour, outer wall pectic, inner wall callose, with callose plugs, penetration of ovules via micropyle [porogamous], whole process takes ca 18 hours, distance to first ovule 1.1-2.1 mm; male gametes lacking cell walls, flagellae 0, double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; seed exotestal, becoming much larger than ovule at time of fertilization; endosperm diploid, cellular [micropylar and chalazal domains develop differently, first division oblique, micropylar end initially with a single large cell, divisions uniseriate, chalazal cell smaller, divisions in several planes], copious, oily and/or proteinaceous; embryogenesis cellular; germination hypogeal, seedlings/young plants sympodial; Arabidopsis-type telomeres [(TTTAGGG)n]; 2C genome size 1-8.2 pg [1 pg = 109 base pairs], whole genome duplication, ndhB gene 21 codons enlarged at the 5' end, 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 three copies of the PHY gene, [PHYB [PHYA + PHYC]].

[NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]]: vessels +, elements with elongated scalariform perforation plates; wood fibres +; axial parenchyma diffuse or diffuse-in-aggregates; pollen monosulcate [anasulcate], tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

[AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood 0; tectum reticulate; anther wall with outer secondary parietal cell layer dividing; carpels plicate; nucellar cap + [character lost where in eudicots?]; 12BP [4 amino acids] deletion in P1 gene.

[[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]] / MESANGIOSPERMAE: benzylisoquinoline alkaloids +; polyacetate derived anthraquinones + [?level]; outer epidermal walls of root elongation zone with cellulose fibrils oriented transverse to root axis; P more or less whorled, 3-merous [possible positiion]; embryo sac bipolar, 8 nucleate, antipodal cells persisting; endosperm triploid; ?germination.

[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (veins in lamina often 7-17mm/mm2 or more [mean for eudicots 8.0]); (stamens opposite [two whorls of] P); (pollen tube growth fast).

MONOCOTYLEDONS / MONOCOTYLEDONEAE / LILIANAE Takhtajan

Plant herbaceous, perennial, rhizomatous, growth sympodial; non-hydrolyzable tannins [(ent-)epicatechin-4] +, neolignans, benzylisoquinoline alkaloids 0, hemicelluloses as xylans; root apical meristem?; root epidermis developed from outer layer of cortex; trichoblast in atrichoblast [larger cell]/trichoblast cell pair further from apical meristem, in vertical files, or hypodermal cells dimorphic; endodermal cells with U-shaped thickenings; cork cambium in root [uncommon] superficial; root vascular tissue oligo- to polyarch, medullated, lateral roots arise opposite phloem poles; primary thickening meristem +; vascular bundles in stem scattered, (amphivasal), closed, vascular cambium 0; vessel elements in root with scalariform and/or simple perforations; tracheids only in stems and leaves; sieve tube plastids with cuneate protein crystals alone; stomata parallel to the long axis of the leaf, in lines, brachyparacytic; leaves with broad sheath plus blade [not petiole plus lamina], blade linear, main venation parallel, veins joining successively from the outside at the apex, endings not free, margins entire, (teeth spiny), Vorläuferspitze +, leaf base sheathing, sheath open, colleters [intravaginal squamules] +; prophyll single, adaxial; inflorescence terminal, racemose; flowers 3-merous [6-merous to the pollinator?], polysymmetric, pentacyclic; P = T, each member with three traces, median member of outer whorl abaxial, aestivation open, members of whorls alternating, similar, [pseudomonocyclic, each providing a sector for the T tube when present]; stamens = and opposite each T member [primordia often associated, and/or A vascularized from tepal trace], anther and filament more or less sharply distinguished, anthers subbasifixed, endothecium from outer secondary parietal cell layer, inner secondary parietal cell layer dividing; G [3], with congenital intercarpellary fusion, opposite outer tepals [thus median member abaxial], placentation axile; ovule with outer integument often largely dermal in origin, parietal tissue 1 cell across; antipodal cells persistent, proliferating; fruit a loculicidal capsule; seed testal; endosperm with distinct nuclear and chalazal chambers, embryo long, cylindrical, cotyledon 1, apparently terminal, plumule apparently lateral; primary root unbranched, not very well developed, "adventitious" roots numerous, hypocotyl short, (collar rhizoids +), cotyledon with a closed sheath, unifacial [hyperphyllar], both assimilating and haustorial; duplication producing monocot LOFSEP and FUL3 genes, [latter duplication of AP1/FUL gene], PHYE gene lost. (Some synapomorphies - almost whatever the immediate sister taxa to monocots might be - are in bold.)

[ALISMATALES [PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]]: ethereal oils 0; raphides + (druses 0); leaf blade vernation variants of supervolute-curved; endothecium develops directly from undivided outer secondary parietal cells; tectum reticulate with finer sculpture at the ends of the grain, endexine 0; (septal nectaries + [intercarpellary fusion postgenital]).

[PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]: cyanogenic glycosides uncommon; starch grains simple, amylophobic; leaf blade developing basipetally from hyperphyll/hypophyll junction; epidermis with bulliform cellls [?level]; stomata anomocytic, (cuticular waxes as parallel platelets); colleters 0.

[[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]: nucellar cap 0; endosperm nuclear [but variation in most orders].

Evolution. Divergence & Distribution. The optimisation of nuclear endosperm to this node of the tree (Tobe & Kadokawa 2010) may well not hold up; variation in endosperm development is great in many orders.

Plant-Animal Interactions. Larvae, and sometimes also adults, of the Chrysomelidae-Criocerinae are scattered throughout this clade, being perhaps especially common on commelinids (e.g. Schmitt 1988; Gómez-Zurita et al. 2007).

[DIOSCOREALES + PANDANALES]: outer integument 2(-3) cells across.

Evolution. Divergence & Distribution. The divergence of these orders is dated to ca 124 m.y. (Janssen & Bremer 2004) or ca 134.4 and 119.6 m.y. for relaxed and constrained penalized likelihood datings respectively (Magallón & Castillo 2009).

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

DIOSCOREALES Martius  Main Tree, Synapomorphies.

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

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...

Evolution. Divergence & Distribution. Stem-group Dioscoreales are dated to ca 124 m.y. , the crown group to ca 123 m.y. (Janssen & Bremer 2004); comparable figures are ca 134.4 and 119.6 (stem) and 101.4 and 115.1 (crown) m.y. (Magallón & Castillo 2009: relaxed and constrained penalized likelihood datings respectively).

Chemistry, Morphology, etc. The tepals of Narthecium ossifragum have three traces, those of Dioscoreaceae a single trace.

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 in the order, see Caddick et al. (2000a: floral morphology and development, 2000b: general); prolongations of the anther connective are homoplasious.

Phylogeny. Nartheciaceae are rather consistently placed with the other Dioscoreales, albeit sometimes with only moderate support (e.g. Chase et al. 2000a; Caddick et al. 2002a; Tamura et al. 2004a: 97% bootstrap, Nartheciaceae well sampled, but otherwise only Dioscorea, Tacca and three Pandanales; Janssen & Bremer 2004: one gene, 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.

Evidence is mounting that the myco-heterotrophic members of Dioscoreales do not come close to forming a clade. Merckx et al. (2006: good sampling, no outgroup to Dioscoreales), using both mitochondrial and nuclear genes, found substantially different relationships within Dioscoreales from those depicted in the tree given by Caddick et al. (2002a: see also /APweb/ version 6 [November] and earlier, classification as in Caddick et al. 2002b). However, as Merckx et al. (2006) note, the relationships found by Caddick et al. (2002a) were dominated by chloroplast data, and since Burmanniaceae s.l. are largely myco-heterotrophic they have much diverged plastid sequences. Indeed, Geomitra, apparently Thismiaceae without any doubt, nevertheless came out with Burmanniaceae in some analyses (Caddick et al. 2002a), while in mitochondrial genome analyses they were widely separated, Burmannia being sister to [Pandanales + Narthecium], while Thismia was in Dioscoreales (G. Petersen et al. 2006b). Some genes, at least, show accelerated evolution (G. Petersen et al. 2006b; Merckx et al. 2006). The positions of Dioscoreaceae and [Taccaceae + Thismiaceae] are sometimes reversed (Yokoyama et al. 2008: support slight). The situation is becoming yet more complex, since Merckx and Bidartondo (2008) and Merckx et al. (2009a) suggest that Thismiaceae s. str. may be paraphyletic, Afrothismia being sister to [Taccaceae + rest of Thismiaceae]. Mercx et al. (2010a) confitmed the paraphyly of Thismiaceae, and also suggested that Trichopus could be sister to [Taccaceae + Thismiaceae]. The basic phylogenetic structure of Dioscoreales remains unclear.

Classification. The classification below follows that suggested by Merckx et al. (2006), although for relationships within Dioscoreaceae in the sense recognized here, see Caddick et al. (2002a, b). Clearly, if the tree suggested by Mercx et al. (2010a) holds up, Afrothismia and Trichopodaceae will have to be split off, or...



Includes Burmanniaceae, Dioscoreaceae, Nartheciaceae, Taccaceae, Thismiaceae.

Synonymy: Burmanniales Martius, Nartheciales Reveal & Zomlefer, Taccales Dumortier, Tamales Dumortier

NARTHECIACEAE Bjurzon   Back to Dioscoreales

Nartheciaceae

Chelidonic acid +, flavonols 0; air spaces in root cortex; fibers intermixed in phloem; (sieve tube plastids with large polygonal crystal - Narthecium); endodermal cells evenly thickened [distribution around here?]; raphides 0, usu. druses +, but prismatic crystals in bundle sheath; cuticular wax with parallel platelets; leaves spiral (equitant and isobifacial [oriented edge on to the stem]); 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, (stylulus long); ovules many/carpel, ana-campylotropous, integuments lack cuticle [check], integumentary obturator + [Aletris]; antipodal cells not multinucleate; seeds obliquely stacked, (with appendages), shape various; tegmen flattened, persistent, or testa cells flattened, (esp. outer anticlinal walls of exotegmen thickened - Lophiola); endosperm helobial, [how much?, walls?]; embryo size?; n = (12) 13 (21, 22), 0.7-1.4 µm long; cotyledon bifacial or not, ?collar rhizoids.

4-5[list]/41: Aletris (30). Interrupted N. temperate, Venezuela and Guiana and scattered in W. Malesia (map: from Hultén & Fries 1986; Jessop 1979; Fl. China 24. 2000; Fl. N. Am. 26: 2002). [Photo - Inflorescence]

Evolution. Divergence & Distribution. Stem-group Nartheciaceae are dated to ca 123 m.y., the crown group to ca 76 m.y. (Janssen & Bremer 2004).

Chemistry, Morphology, etc. Metanarthecium may have abaxial prophylls. There are reports that the ovules of Narthecium may be unitegmic (Remizowa et al. 2006a). In general, variation in floral development is considerable, and the ovary may even be secondarily superior in Metanarthecium (Remizowa et al. 2008a; Fuse et al. 2012).

Additional information: For embryology, see Ono (1929) and Cave (1968), for seed coat, see Takhtajan (1985: as Hypoxidaceae), for inflorescence and flower development, see Remizowa et al. (2006a, b), for endodermal thickening, see Zomlefer (1997a), for leaf anatomy, see Luque Arias et al. (2006), and for pollen morphology, see Merckx et al. (2008b).

Phylogeny. Aletris, with its spiral and bifacial leaves, was sister to the three other genera examined (Tamura et al. 2004a), while Metanarthecium had weak support as sister to the rest of the family in Fuse et al. (2012). Although genera like Lophiola and Narthecium have equitant, isobifacial leaves, they are unlikely to be an apomorphy for the family.

Previous Relationships. The relationships of Nartheciaceae, with their rather ordinary-looking monocot flowers, have long been problematic. Cronquist (1981) did not even mention them, but they would probably have been included in his highly heterogeneous Liliaceae, Dahgren et al. (1985) placed them - along with representatives of Tofieldiaceae (here Alismatales) and Petrosaviaceae (Petrosaviales) - in Melianthaceae (Liliales), and Tamura (1998) placed them in Petrosaviaceae, along with genera here included in Tofieldiaceae.

Synonymy: Lophiolaceae Nakai

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

Evolution. Divergence & Distribution. Divergence times of the two main clades are (118-)109-79-75(-52) m.y. The myco-heterotropic habit may have evolved some time before the beginning of the Palaeocene (83-)63(-45) m.y.a. when Afrothismia gesnerioides diverged from the rest of the Taccaceae-Thismiaceae clade (Merckx et al. 2010a).

Endress (2011a) thought that the inferior ovary in Dioscoreales might be a key innovation.

Myco-heterotrophy has evolved at least three, perhaps six times in this clade (Merckx et al. 2006, 2009, 2010a); Glomeromycota seem to be the fungi involved (Franke et al. 2006).

Chemistry, Morphology, etc. Cell walls in the endosperm are often thick, but are usually not pitted. The embryos of Taccaceae and Diocoreaceae are similar in their more or less lateral cotyledon (Solms Laubach 1878).

[Taccaceae + Thismiaceae]: T whorls differentiated, but both well developed and petal-like; A incurved; septal nectaries 0; placentation parietal, stigmas broad; ovules many/carpel.

TACCACEAE Dumortier, nom. cons.   Back to Dioscoreales

Taccaceae

Plant with stem tubers or rhizomes, secondary thickening + (?); vessels 0; hairs with multicellular stalk row, a head, and then another cell row; petiole bundles in ring; leaves basal, lamina margins entire or ± deeply pinnately or palmately divided, venation reticulate, petiolate, base somewhat sheathing; inflorescence scapose, umbellate, of groups of cincinni, inflorescence bracts petal-like, floral bracts long, filiform, among the flowers; flowers medium in size; T with median member of outer whorl adaxial, tube short; A adnate to P at base, connective broad, not prolonged, forming a hood around anther; middle layer of anther wall from outer secondary parietal cells; G opposite C/inner T, stylar canal with secretion, stigma often petal-like; nucellar cells laterally anticlinally expanded, nucellar cap 0; megaspore mother cells several; fruit a berry (capsule); seed ribbed; (endotesta crystalliferous), exotegmen ± thick-walled and elongated, esp. radially; embryo short to minute, cotyledon ± lateral; n = 15; cotyledon ?bifacial, sheath lobed.

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

Evolution. Pollination Biology. The dark purple flowers of most species of Tacca and the long, dangling bracts suggest some sort of fly pollination. The inflorescence as a whole can be strongly monosymmetric, as in Tacca integrifolia; there two large and conspicuous white inflorescence bracts are held above the dark purple flowers and less conspicuous lower inflorescence bract and the whitish dangling filiform bracts.

Chemistry, Morphology, etc. Tacca seems to lack the distinctive vasculature of Dioscoreaceae, in which it used to be included. It is unclear if the midrib is distinct or multistranded (Inamadar et al. 1983). The flowers are drawn with the odd member of the outer whorl in the adaxial position by Ronse de Craene (2010). 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), for xylem anatomy, see Carlquist (2012a).

THISMIACEAE J. Agardh nom. cons.   Back to Dioscoreales

Thismiaceae

Plants myco-heterotrophic; saponins?; roots coralloid, vermiform ot tuberous, root hairs 0; stomata 0; leaves reduced to scales, (borne immediately below the flower); flowers often single or in (branched) inflorescences; (flowers monosymmetric); T with single trace, (whorls not differentiated), (apex of inner P whorl members long and slender, often connate and the whole like a "mitre", contorted - Thismia, etc. - outer P lobes then small or even 0), annulus or ring of short projections at mouth of tube + [0 - Haplothismia], T tube well developed and expanded below attachment of A at apex, with intrastaminal lobes; A (3, opposite inner T, Oxygyne), inflexed in flower [more or less hanging down and the anthers then seemingly extrorse], ± connate, (adnate to stigma), thecae with prolonged connective, filaments variously ornamented; tapetal cells uninuclear; pollen (trinucleate), porate; placentae as separate columns, often ± free from walls, ± apical, style connate at least early in ontogeny, branches slightly dorsi-ventrally flattened, (undivided), stigmas capitate to elongated; ovules lacking parietal tissue, funicles long [?all]; (embryo sac bisporic); fruit irregularly dehiscent, T basally 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; n = 6-9, chromosomes 1-4 µm long.

5/45: Thismia (35), Afrothismia (12). Widely scattered, mostly (sub)tropical (map: from Jonker 1938; van Steenis & van Balgooy 1966; Maas et al. 1986; Larsen & Averyanov 2007; Dauby et al. 2008; Ho et al. 2010). [Photo - Thismia.]

Evolution. Divergence & Distribution. The immediate relatives of Thismia americana, once collected near Chicago but now apparently extinct, are Antipodean (Thorne 1992).

Bacterial/Fungal Associations. Merckx and Bidartondo (2008) described what they called delayed co-speciation (the delay is 65-170 m.y.!) of a group of Afrothismia on/with their Glomus fungal symbiont. Glomeromycote fungi form quite specific associations with species of Thismiaceae (Merckx et al. 2012).

Pollination Biology. 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). There are no nectaries (Caddick et al. 2000).

Chemistry, Morphology, etc. The stems may be endogeneous in origin (Pfeiffer 1914). The morphology of the inflorescences of species of Thismia described by Larsen and Averyanov (2007) is not easy to understand.

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

Phylogeny. As mentioned above, Merckx et al. (2009a, 2010a) suggested that Thismiaceae s. str. may be paraphyletic, relationships perhaps being [Afrothismia [Taccaceae + rest of Thismiaceae]] - or [Afrothismia [Trichopodaceae [Taccaceae + rest of Thismiaceae]]]. Relationships between other Thismiaceae are unclear, although Thismia itself may also be paraphyletic (Merckx et al. 2009a).

The inflorescence of Afrothismia hydra appears to be cymose (Imhof & Sainge 2008). The plane of symmetry of the flowers is not easy to interpret, thus Afrothismia amietii apparently has two adjacent tepals much longer than the other four; see also the floral diagram in Maas-van de Kamer (2003). The seedling is also not easily describable (Imhof & Sainge 2008).

Some information is taken from Cheek (2003b) and Maas-van de Kamer (2003).

Classification. Most Thismiaceae are small plants with small and inconspicuous flowers and are not often found in flower - and judging by the continuous stream of new species and even genera that are being described, extremely poorly known on even an alpha taxonomic level (see Franke 2007: comments on distributions).

[Burmanniaceae + Dioscoreaceae]: fruit winged.

BURMANNIACEAE Blume, nom. cons.   Back to Dioscoreales

Burmanniaceae

Plants myco-heterotrophic, (chlorophyllous - some Burmannia), roots ± fleshy, or root tubers +; saponins?; (root hairs 0); (root stele solid); (stem with vascular bundles in a single ring); raphides 0; (stomata 0), (cuticular waxes as platelets transversely arranged in parallel series); leaves (two-ranked), usu. reduced to scales; (bracteoles lateral - Burmannia); (flowers monosymmetric), T (moderately large), valvate, (lobed), outer larger, enclosing the inner, (inner 0), T tube well developed and expanded below attachment of A; A 3, opposite inner T, incurved and ± associated with style, connective broad, thecae widely separate, lateral, transversely dehiscent; pollen often trinucleate, monoporate, sulcate or inaperturate, psilate; placentation ± parietal, (axile - Burmannia), (paired glands [modified septal nectaries] at apex of each placenta), style long, (branches with paired long-filiform receptive[?] appendages), stigmas ± capitate (with a long, thin, apical process); ovules many/carpel, parietal tissue absent, chalazal tissue quite conspicuous, persistent; (antipodal cells persist - Gymnosiphon); fruit winged, transversely (Burmannia) or longitudinally septicidal and/or loculicdal dehiscent down the sides, or indehiscent, T persistent, (circumscissile at the middle of the tube); seeds minute; testal cells ± spiral, ± elongated, tegmic cells compressed, (tanniniferous); endosperm usu helobial, thick-walled, with starch when young, not persisting, [cell formation in chalazal endosperm chamber first], chalazal endosperm semi-haustorial?; 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.]

Evolution. Divergence & Distribution. Stem group Burmanniaceae are dated to ca 116 m.y., the crown group to ca 93 m.y. (Janssen & Bremer 2004: three genera sampled); there are similar dates in Merckx et al. (2008a).

The rather wide geographical range of the family has been achieved largely by migration, and diversification rates were notably high in the Eocene (Merckx et al. 2008a).

Bacterial/Fungal Associations. There has been more than one loss of chlorophyll in Burmanniaceae (Merckx et al. 2006). In at least some non-myco-heterotrophic species of Burmannia, the plant can grow well under high light conditions without any association with arbuscular mycorrhizal fungi (Merckx et al. 2010b).

Chemistry, Morphology, etc. The root stele is di- to pentarch and may lack a pith. Although roots of Burmanniaceae are often described as lacking root hairs (e.g. Maas-van der Kamer 1998), as might befit their close association with fungi, root hairs are shown in Burmannia (von Guttenberg 1968). In echlorophyllous taxa vessels may be restricted to the roots, in others there are vessels in the leaves.

Rübsamen (1986) suggests that Burmnanniaceae lack nectaries. In a floral diagram (Eichler 1874) the stigmas are shown as being commissural.

Information is taken from Johow (1889 and references: anatomy, embrylogy), and Dahlgren et al. (1985), Rübsamen (1986) and Maas-van der Kamer (1998), all general.

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

Lianes or vines, climbing by twining; (saponins 0), norditerpenes +; flavonols +; in the stem 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 with scalariform perforation plates, in petiole but not lamina; stomatal ontogeny irregular; hairs glandular; (prophylls lateral); lamina vernation conduplicate, with midrib and reticulate fine venation, (vein endings free), petiolate, petiole pulvinate at both ends, leaf base not sheathing; inflorescences axillary; microsporogenesis simultaneous [tetrads tetrahedral]; carpels plicate, filled with secretion [Stenomeris, Trichopus?], compitum +, stigma wet; ovules with bi(endo-)stomal micropyle, (outer integument ³3 cells across); seeds winged; endotestal cells elongated, thick-walled, with crystals (0), exotegmen thickened; embryo broad, cotyledon ± lateral.

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

1. Stenomeris Planchon

Underground stem thickened; tannin cells 0; petiole bundles in arc; hairs with two-celled gland heads; T tube well developed and expanded below attachment of A; A inserted in mouth of T tube, A inflexed in flower [more or less pendulous, the anthers seemingly extrorse], connective prolonged; microsporocytes markedly elongated; G half inferior; ovules many/carpel; tegmen collapsed; n = ?; seedling?

1/2. W. Malesia.

Synonymy: Stenomeridaceae J. Agardh

[Trichopus + Dioscorea]: plant monoecious to dioecious; anther connective broad; ovules (1) 2/carpel, superposed, hypostase +; endosperm walls thickened.

2. Trichopus Gaertner

<i>Trichopus</i>

Rhizomatous, stem ± climbing; flavones +; endodermoid layer fibrous; hairs with many transversely elongated cells in series in gland heads [Trichopus s. str.]; petiole bundles in arc; petiole with basal pulvinus only (Avetra s. str. - 0); staminate flowers: A incurved, anther connective broad, prolonged, pushing up between style branches; microsporocytes markedly elongated; pollen spinulose; nectary 0; carpellate flowers: ovule (1/carpel), parietal tissue absent, nucellar cap 0, lateral nucellar cells +, obturator +; fruit dry, ± indehiscent, winged [samara], or semi-berry; seed not winged, with irregular intrusions; endotesta not thickened, exotegmic cells elongated, with reticulate thickenings; endosperm ruminate, embryo minute; n = 14, chromosomes 1.5-2.7 µm long; germination?

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

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

3. Dioscorea L.

<i>Dioscorea</i>

Tubers +, hypocotylar; chelidonic acid, (mannans) +; (secondary thickening +); sieve tube plastids also with protein crystals and starch grains; petiole bundles in ring (not D. hemicrypta); stomatal morphology odd; gland heads many celled; leaves two-ranked (opposite), flat to curved or conduplicate, (lobed), (palmately compound), (midrib +), (base with paired evascular processes); serial buds common; plant dioecious, inflorescences two or more together, (bracteoles lateral); flowers small, T free or connate, with a single trace; staminate flowers: A (1) 3 (6), adnate to T or free (connate), (extrorse; anther connective prolonged); pollen often disulcate; pistillode +; carpellate flowers: staminodes +; stylar canal with secretion, stigma usually not bilobed; ovule with outer integument 4-5 cells across, nucellar cap ca 3 cells across, supra-chalazalal tissue ± massive, hypostase +; fruit capsular, baccate, or samaroid; (seeds not winged); testa multi-layered, endotestal cells usu. crystaliferous, with phlobaphene, exotegmen sclerotic [with branched protrusions of the cells walls], endotesta crystaliferous, exotegmen usu. thick-walled, endotegmen tanniniferous, (wing formed by chalazal area and by the testa - D. oppositifolia); endosperm usu. (very) thick-walled, embryo small to medium; n = (7, 8), 9, 10 [up to 14-ploid], 12, chromosomes 0.3-2.7 µm long (Epipetrum - chromosomes 1.9-2.9 µm long); cotyledon flattened and photosynthetic or not, second leaf a scale leaf.

1/350-?800. Largely tropical, also warm temperate, esp. seasonal (map: see Meusel et al. 1965; Fl. N. Am. 26: 2002; FloraBase 2004). [Photo - Inflorescence, Flower, Fruits.]

Synonymy: Tamaceae Berchtold & J. Presl, Tamnaceae J. Kickx f.

Evolution. Divergence & Distribution. Stem group Dioscoreaceae are dated to ca 116 m.y., the crown group to ca 80 m.y. (Janssen & Bremer 2004).

Chemistry, Morphology, etc. Dioscorea batatas has storage mannans in its vegetative tissues (Meier & Reid 1982). The cork in the tubers of Dioscorea is subepidermal and there may be secondary thickening; the exact morphological nature of the tuber is in some dispute. The vascular bundles in the stem may be arranged in a ring. For midrib anatomy, see Edeoga and Ikem (2001). Compound leaves are the result of localised activity in the marginal blastozone (Periasamy & Muruganathan 1985; Gunawardena & Dengler 2006). Lateral prophylls occur at least sometimes.

The flowers of Dioscorea are shown with the median member of the outer whorl in the adaxial position (Spichiger et al. 2004). The thickness of the parietal layer of the ovule is taken from Torshilova et al. (2003); Nagaraja Rao (1953) described it as being massive, and it could be interpreted as being 6-8 cells across. Seed coat anatomy would repay attention (Huber 1998). Huber (1998) noted that the mechanical layer of the seed coat was the exotegmen, but in Nagaraja Rao (1953) the endotesta of Dioscorea oppositifolia is shown as consisting of small, heavily U-thickened and crystal-bearing cells.

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 the microsporogenesis of Avetra, see Caddick et al. (1998, 2000b).

For additional information, see Burkill (1960), Conran and Clifford (1985), Huber (1998), and Viruel et al. (2010), all general, for anatomy, Ayensu (1972) and Behnke (1990b: nodal anastomoses), for ovules, Igersheim et al. (2001), for ovules and seeds, Nagaraja Rao (1955 {Trichopus]), and Torshilova and Titova (2010), for chromosome numbers, etc., Viruel et al. (2008), and for pollen evolution, Schols et al. (2005b).

Phylogeny. Much more detailed information is provided by Caddick et al. (2002b). For the circumscription of Dioscorea and relationships within the genus, see Bharathan et al. (2001), Caddick et al. (2002a), and Wilkin et al. (2005).

Classification. Descriptions are provided for all three genera since they have usually been placed in separate (albeit more or less closely related) families. The phylogeny of Dioscorea and genera immediately related to it suggests that taking a broad view of Dioscorea is desirable. Dioscorea s. str. was divided into 22 sections by Huber (1998), and all were fully described, but having 22 genera would not seem a desirable option.