Thunbergia usambarica Lindau

Acanthaceae (part 1), Kaj Vollesen, Flora of Tropical East Africa, 2008

Morphology General Habit

Erect or straggling perennial herb from creeping woody rootstock; stems to 1 m long, quadrangular, glabrous to puberulous (rarely pubescent), with conspicuous bands of glossy setose hairs at nodes.

Morphology Leaves

Leaves thin, glossy, palmately veined; petiole 1–10 cm long, puberulous and distinctly ciliate; lamina ovate or broadly so (rarely oblong-lanceolate), largest (4–)6–14(–16.5) × (2.3–)3–7.5(–10.5) cm, apex acute to acuminate (rarely obtuse), apiculate, base subcordate to deeply cordate with rounded to hastate lobes, margin entire to crenate (rarely sharply dentate), glabrous to puberulous, mainly on veins or with longer glossy setose hairs on veins.

Morphology Reproductive morphology Flowers

Flowers solitary (rarely paired or very rarely in 3’s); pedicels 2–6(–7) cm long, glabrous (rarely sparsely puberulous near apex); bracteoles green, with conspicuous raised dark green reticulation, lanceolate- or ovate-oblong, 1–1.9 × 0.4–0.8(–1) cm, acute, with sparse to dense long (to 2 mm) glossy glandular hairs on veins and margins, more rarely glabrous.

Morphology Reproductive morphology Flowers Calyx

Calyx minutely puberulous, 1–3(–5 in fruit) mm high of which the broadly triangular lobes about half.

Morphology Reproductive morphology Flowers Corolla

Corolla white with yellow throat, more rarely pale lilac; tube 2–3.2 cm long; lobes 1–1.5(–2) × 1.5–2(–2.5) cm.

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filaments 7–9 mm long, basal part glandular; anthers 2–2.5 mm long.

Morphology Reproductive morphology Flowers Gynoecium Style

Style with scattered glands.

Morphology Reproductive morphology Fruits

Capsule 8–9 mm in diameter, beak 14–16 mm, long.

Morphology Reproductive morphology Seeds

Seed reddish brown, ± 6 mm in diameter, reticulate to spinulose near apex.

Distribution

Range: Uganda. Range: Congo-Kinshasa, Rwanda, Burundi, Malawi, Mozambique, Zimbabwe, South Africa Flora districts: U2 K3 K5 T2 T3 T5 T7 T8 Range: Kenya. Range: Nandi District: Kapsabet, Yala River, no date, Range: Congo-Kinshasa, Rwanda, Burundi, Malawi, Mozambique, Zimbabwe, South Africa Range: Tanzania.

Ecology

Wet evergreen montane forest, often on margins, in clearings and in disturbed areas; (1350–)1650–2450 m

Note

The only two collections ( Hornby 498 & 2062) seen from T 5 (Kiboriani Mt) differ from all other material in the very wide shortly petiolate leaves but are otherwise quite typical. This locality is very isolated from the rest of the distribution area in Tanzania, and further collections are needed to prove whether this form might be worthy of taxonomic recognition. Ecologically the two are more or less separate with T. usambarica growing at higher altitudes. Very similar to T. petersiana from which it differs in a smaller usually white corolla.

J. R. Timberlake, E. S. Martins (2013). Flora Zambesiaca, Vol 8 (5) Acanthaceae Part 1. Royal Botanic Gardens, Kew

Type

Tanzania, Lushoto Dist., Usambara Mts, xii.1891, Holst 215 (B† holotype, K).

Morphology General Habit

Erect or straggling perennial herb from a creeping woody rootstock; stems to 1 m long, quadrangular, glabrous to puberulous, densest below nodes, conspicuous bands of glossy setose hairs at nodes

Morphology Leaves

Leaves glossy, palmately veined, glabrous to puberulous, mainly on veins or with longer glossy setose hairs on veins; petiole 1.5–10.5 cm long, upper leaves often subsessile; lamina ovate, rarely oblong-lanceolate, usually widest well above basal lobes, largest 8–15.5 × 4–9.5(11) cm; apex acute to acuminate, base subcordate to deeply cordate with rounded to hastate lobes; margin crenate to coarsely toothed with up to 7 large teeth per side

Morphology Reproductive morphology Flowers

Flowers solitary, rarely paired or in racemes from lower axils; pedicels 2–5(10 in fruit) cm long, glabrous or sparsely puberulous near apex; bracteoles pale green, with conspicuous raised dark green reticulation, 0.9–2.5 × 0.4–1.4 cm, lanceolate- or ovate-oblong, acute, glabrous or with sparse to dense long (to 2 mm) glossy glandular hairs on veins and margins

Morphology Reproductive morphology Flowers Calyx

Calyx minutely puberulous, 1–3(5 in fruit) mm long, the broadly triangular lobes about half

Morphology Reproductive morphology Flowers Corolla

Corolla white with yellow throat, rarely pale blue; tube 2–3.5 cm long; lobes 1–1.5(2) × 1.5–2(2.5) cm

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filaments 8–10 mm long, basal part glandular; anthers 2–2.5 mm long; style with scattered glands or glabrous

Morphology Reproductive morphology Fruits

Capsule 7–10 mm wide, beak (10)12–18 mm long

Morphology Reproductive morphology Seeds

Seeds dark brown, 5–6 mm in diameter, reticulate to spinulose near apex.

Distribution

Zimbabwe, Malawi, Mozambique. Also in Congo, Burundi, Uganda, Kenya, Tanzania and South Africa.

Ecology

In montane forest, often on margins, in clearings and in disturbed areas, persisting in plantations; (1100)1400–2500 m.

Conservation

Widespread; not threatened.

Recognition

Very similar to Thunbergia petersiana from which it differs in the smaller usually white corolla. The differences in leaf shape and dentation are also distinctive. Ecologically the two are more or less separate with T. usambarica growing in wetter forest types at higher altitudes and T. petersiana usually in drier forest at lower altitudes.