Duosperma Dayton

Acanthaceae (part 2), Kaj Vollesen. Flora of Tropical East Africa. 2008

Morphology General Habit

Perennial or shrubby herbs or shrubs, with usually conspicuous linear cystoliths (especially on calyx); stems terete to distinctly quadrangular; bark on older branches usually peeling off in flakes or strips

Morphology Leaves

Leaves opposite, with strong unpleasant smell when crushed; basal part of petiole forming a stipule-like sheath around the stem

Morphology Reproductive morphology Flowers

Flowers subsessile or petiolate, solitary or in condensed axillary cymes which sometimes merge into large panicles; bracteoles usually large and conspicuous, often foliaceous

Morphology Reproductive morphology Flowers Calyx

Calyx leathery, 5-lobed, fused in basal part, splitting in fruit; lobes lanceolate to triangular, with strong rib-like central vein and with scarious margins, dorsal lobe usually distinctly longer and wider than the rest, 2 ventral lobes fused higher up

Morphology Reproductive morphology Flowers Corolla

Corolla contorted in bud, distinctly 2-lipped; tube cylindric at base, widening into a dictinct throat which is hairy ventrally; upper lip 2-lobed, erect, sometimes slightly hooded, lower lip 3-lobed, deflexed, lobes all similar, but wider in lower lip, lower lip pleated at base, with or without long stiff hairs

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 4, inserted just inside cylindric part of tube, didynamous (longer pair 1–2 mm longer than short pair), held under upper lip, the two short stamens occasionally reduced to staminodes; filaments fused with tube, fused part running like two puberulous longitudinal ridges to base of tube, free part of each long and short filament fused at base; anthers 2-thecous, thecae oblong, rounded or apiculate at both ends, never with spurs

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary with 1–2 ovules per locule.

Morphology Reproductive morphology Flowers Gynoecium Style

Style filiform, with upwardly directed hairs.

Morphology Reproductive morphology Flowers Gynoecium Stigma

Stigma lobes 2, linear, equal or dorsal about half the length of ventral

Morphology Reproductive morphology Fruits

Capsule (1–)2-seeded, ellipsoid-obovoid, woody, glossy, laterally compressed, usually glabrous, valves sulcate dorsally; retinaculae strong, hooked

Morphology Reproductive morphology Seeds

Seed discoid, ovoid to orbicular in outline, with hygroscopic hairs.

Note

Duosperma is morphologically very similar to Dyschoriste and Hygrophila but palynological work (Vollesen l.c.) strongly implies that it is closer to Mellera, Mimulopsis and Eremomastax. It differs from Dyschoriste and Hygrophila in the laterally compressed 2-seeded capsule and in having a style with both stigma lobes well-developed. The large conspicuous bracteoles also provide a useful spot-character.  The capsules usually persist on the plant until next rainy season. The apical part (base of style) is thickened and slightly bulbous and only tardily dehiscent.

Distribution

Range: 26 species in eastern and southern tropical Africa from Somalia and S Ethiopia to Botswana and Angola. One species extends to Yemen. Particularly diverse from central and SW Tanzania into N Zambia and SE Congo.