Dioscorea buchananii Benth.

Wilkin, Paul & Muasya, A. Muthama, 2015, Clarifying the Dioscorea buchananii Benth. species complex: a new potentially extinct subspecies for South Africa, PhytoKeys 48, pp. 51-72 : 54

Dioscorea buchananii Benth.

Dioscorea buchananii Benth., Hooker’s Icon. Pl. 14:76, t. 1397, 1398 (1882).

Dioscorea buchananii var. ukamensis R.Knuth in H.G.A Engler (ed.), Pflanzenr. 4, 43: 185 (1924). Type: Tanzania, Morogoro Dist., Ukami, without date, Stuhlmann 8283 (holotype: B†).

Dioscorea mildbraediana R.Knuth, Notizbl. Bot. Gart. Berlin-Dahlem 11: 1059 (1934).

Dioscorea buchananii Type: Tanzania, Kilwa, Mswega, ♂ fl. 22 Jun 1932, Schlieben 2495 (holotype: B!; isotype BR!).

Dioscorea rhacodes Peter ex R.Knuth, Repert. Spec. Nov. Regni Veg. 42: 162 (1937).

Dioscorea buchananii Type: Tanzania, Ukami, east of Morogoro, ♂ fl. 1926, Peter 46419 (holotype: B!).

Types.

Malawi: Shire Highlands, ♂ fl. 1881, Buchanan 173 (syntype: K!) ♀ fr. 1881, Buchanan 358 (syntype: K!).

Description.

Twining vine to 10 m in height, vegetative growth annual, usually 1 shoot per year from apex of perennial, woody tuber, to ca 20 cm in diam., usually globose to ovoid, sometimes elongate or irregular, shape varying perhaps based on rockiness of substrate, externally dark grey to brown, fissured, bark-like. Indumentum absent. Stems left-twining, to 5 mm in diam., terete to shallowly longitudinally ridged, more so when dry, unarmed from base, green or purple-hued, herbaceous, cataphylls not seen. Leaves alternate, blade variable, 2.8-13.5 × 1.1-14.7 cm, entire or with 3, 5 or 7 shallow to deep lobes, ovate to broadly so, veins 7(-9), primary venation in shallow channels on upper surface in fresh material, primary and secondary venation prominent below, base cordate, with a shallow to deep basal sinus, rarely truncate, texture chartaceous, where lobes present central lobe to 116 mm long, lateral lobes to 35 mm long, lobes usually found primarily in vegetative stem leaves with reproductive stem leaves more weakly lobed to entire, rarely consistently lobed to shoot apices, lobes inserted from around mid-point to point of petiole insertion, lobe margins entire to (rarely) weakly undulate or in some leaves lobed to stem apices with weak to strong irregularly pinnate secondary lobing, blade or central lobe apex acute to triangularly short-acuminate, rarely obtuse or truncate, bearing a 1.5-10 mm long, thickened, very narrowly triangular, brown forerunner tip fed by the 3 central veins of blade; petiole 0.6-6.3 cm long, ridged like stem and with a narrow channel on upper surface, colour as stem, pulvinii sometimes paler or purple-hued; lateral nodal organs absent but petiole base broader where inserted onto stem, axillary bulbils absent. Inflorescences simple, usually 1 per axil, axes straight, angular, pale green or purple or brown-hued; male 1.6-7 cm long, peduncle 2-11 mm long, racemose, pendent to spreading, usually dense with flowers 0.3-4.1 mm apart and solitary or rarely in cymules of 2-3 flowers, on a 1.7-5.0 mm long pedicel that is angular and slightly broader towards apex, buds patent to axis, pendent at developing inflorescence apex only in very early development; female inflorescence 9-77 mm long, accrescent to ca 30 cm long in fruit, peduncle 12-20 mm long, spicate, pendent, lax, flowers subpendent only at the earliest stages of development, patent to axis at anthesis but ascending to erect soon thereafter. Flowers turbinate in bud, tepals 6, free, inserted on margin of a saucer-shaped, weakly thickened torus, spreading at anthesis, sometimes ascending thereafter, whorls scarcely differentiated, 3-veined, brown, green, olive or bronze, sometimes with a pink or yellow hue or mottled; male flower with floral bract and bracteole sheathing pedicel base, bract 1.6-2.6 mm long, ovate, long-acuminate, membranous, bracteole similar, narrower, usually offset from bract; outer tepals 2.5-4.7 × 1.1-2.3 mm, inner tepals 2.7-4.5 × 1.3-2.3 mm, narrowly ovate to lanceolate or triangular, chartaceous, apex acute to short-acuminate, flat; filaments 0.6-1.8 mm long, erect but incurved over 2.3-5 mm diam. torus, anthers 0.5-1.2 × 0.4-0.8 mm, introrse; pistillode to ca 0.1 mm high, 3 centrally fused triangular ridges at 120° to each other in flat central part of concave torus; female flower with floral bract and bracteole sheathing ovary base, bract 1.6-2.4 mm long, ovate, long-acuminate, membranous, bracteole similar, narrower, usually offset from bract; ovary 5-10 mm long, 3-angled, lorate to very narrowly elliptic in outline, colour as axis, apex constricted; outer tepals 2.9-4.5 × 0.8-1.9 mm, inner tepals 2.9-4.4 × 0.9-2 mm, more or less erect, narrowly ovate to lanceolate, apex acute to short-acuminate, flat, each tepal with 0.2-0.7 mm long basal staminode inserted at the boundary with the torus at the tepal base midpoint, usually fleshy and ovoid but sometimes substaminiform; torus 2.5-4.5 mm in diam. both tepals and torus accrescent as ovary enlarges; style 1.8-3.2 mm long, erect, divided into 3 spreading branches towards apex, stigmas bifid, oblong to clavate. Capsule 2.2-3 × (1.8-)2-3.2 cm, pedicel reflexed and thus ascending to erect at dehiscence, lobes obovate to oblong-obovate in outline, thick-chartaceous, base and apex usually truncate, dry and withered flowers persistent until relatively late in development on a ca 1.2-2.0 mm long stipe, light brown with chestnut-brown to coppery brown mottling, dehiscing apically at least at first. Seed 2.5-4 × 3-4 mm, irregularly lenticular, dark brown wing 1-2 × 0.7-1.3 cm, broadly oblong-elliptic to rotund to irregularly so, wing extending all around seed margin although elongated towards rounded to obtuse base and apex, pale brown, translucent with fine paler speckling.