Acanthus austromontanus Vollesen

Vollesen, K. (2007). Synopsis of the Species of Acanthus (Acanthaceae) in Tropical East and Northeast Africa and in Tropical Arabia. Kew Bulletin, 62(2), 233-249. Retrieved from http://www.jstor.org/stable/20443348

Type

Tanzania, Leedal 7161 (holotypus K!; isotypi DSM, K!).

Morphology General Habit

Shrub to 3(- 4) m tall; young stems puberulous or sparsely puberulous

Morphology Leaves

Leaves beneath puberulous or sparsely puberulous and with longer glossy hairs on midrib and larger veins, glabrous on lamina, above puberulous on midrib, otherwise glabrous; petiole 0.5 - 1(- 2) cm long; lamina elliptic or narrowly elliptic in outline, largest 10 - 19 x 5.5 - 9 cm, deeply lobed with large triangular spine-tipped lobes, each lobe with a single spine on antrorse side; apex acute, spine-tipped; base truncate; stipule-like interpetiolar leaves present (rarely absent), with lamina up to 0.7 cm long, spiny, soon caducous

Morphology Reproductive morphology Flowers

Flowers in terminal racemoid cymes, 7 - 17(- 20 in fruit) cm long; rachis sericeous-tomentose, with several pairs of sterile bracts at base; bracts with 3 prominent longitudinal veins, brown to purple, obovate, sparsely sericeous puberulous or -pubescent, 2.7 - 3.7 cm long in middle of spike, spine-tipped and with 15 - 28 large and small teeth per side, longest 8 - 12 mm, small teeth inserted on large, teeth with scattered hairs near base only, less than 1 mm long

Morphology Reproductive morphology Inflorescences Bracteoles

Bracteoles lanceolate to obovate, 3.2 - 3.8 cm long, toothed in apical 1/2 - 3/4 with up to 25 teeth per side

Morphology Reproductive morphology Flowers Calyx

Calyx divided to base into 4 glumaceous sepals which are thickened and horny at the base, green with purple apical part and teeth and yellow thickened part; sparsely to densely sericeous-pubescent; dorsal 1 - 3 veined, ovate with long parallel-sided apical part, 3.5 - 4 cm long, acute, with 3 - 20 lateral teeth per side, longest tooth 3 - 5 mm long, ventral sepal 2 veined, obovate, 3.4 - 3.8 cm long, with 2 triangular lobes which are acute or 2 - 4-toothed and c. 0.8 cm long, with 6 - 17 lateral teeth per side, longest tooth c. 6 mm long, lateral sepals 1-veined, ovate elliptic, 2.2 - 2.7 cm long, acuminate, without or with up to 12 lateral teeth per side (one side often with more than the other)

Morphology Reproductive morphology Flowers Corolla

Corolla tube white, limb deep purple; tube apically thickened and spongy and with a band of thick retrorse hairs on the inside, 6- 7 mm long below thickened rim which is 8 - 10 mm long and deeply split dorsally; limb deflexed, 5-lobed, 4 - 5.5 x 3 - 3.5 cm, finely and sparsely puberulous above and below, lobes broadly oblong, rounded or central emarginate, three central much longer than two lateral; callus with broad central groove and two narrow lateral ridges

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 4, exserted, inserted just inside throat, two posterior held above anterior; filaments curved, thick and bony, laterally compressed, 2.7 - 3.3 cm long, glabrous; anthers 1-thecous, oblong, with brushes of stiff hairs along whole length ventrally, 4 - 5.5 mm long, with sparse long curly hairs on sides and sessile glands dorsally

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary 2-locular with 2 ovules per locule; style linear, glabrous; stigma of 2 lanceolate, acute lobes

Morphology Reproductive morphology Fruits

Capsule 4-seeded, ellipsoid, glossy, sessile, flattened dorsiventrally and rounded apically, c. 3 cm long; seed (immature) discoid, glabrous, c. 8 x 6 mm.

Distribution

Endemic to the Southern Highlands of Tanzania.

Ecology

Montane grassland and forest margins, occasionally used as a hedge plant; 2000 - 2300 m.

Conservation

Acanthus austromontanus has been collected just five times over a time span of just under 100 years. The last collection is from 1986 but Colin Congdon (pers. comm.) states "there is a fairly common shrubby Acanthus in the grasslands around Milo, but I didn't see it in flower". No other grassland species of Acanthus occurs in this part of Tanzania. The three collections with complete dates were all made in the middle of the dry season. Species flowering at the height of the dry season are often undercollected because very few collectors work at this time, and a mere examination of herbarium material therefore often gives a false impression of the rarity of such species, see e.g. Vollesen (2006: 289). The core habitat of the species is mainly used for grazing and it is, in common with all other grassland species in this group, unpalatable to browsing animals. The greatest risk to its survival is therefore the grass fires which affect most of the Southern Highland grasslands on a yearly basis. McGregor 27 reports that it is used for fencing. Probably Least Concern (LC) but currently Data Deficient (DD).

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

Morphology General Habit

Shrub to 3(–4) m tall; young stems puberulous or sparsely so.

Morphology Leaves

Leaves with petiole 0.5–1(–2) cm long; lamina elliptic or narrowly so in outline, largest 10–19 × 5.5–9 cm, deeply lobed with large triangular spine-tipped lobes, each lobe with a single spine on antrorse side, apex acute, spine-tipped, base truncate, beneath puberulous or sparsely so and with longer glossy hairs on midrib and larger veins, glabrous on lamina, above puberulous on midrib, otherwise glabrous; stipule-like interpetiolar leaves present (rarely absent), with lamina up to 7 mm long, spiny, soon caducous.

Morphology Reproductive morphology Inflorescences

Cymes 7–17(–20 in fruit) cm long; rachis sericeous-tomentose, with several pairs of sterile bracts at base; bracts with 3 prominent longitudinal veins, brown to purple, obovate, sparsely sericeous-puberulous or -pubescent, 2.7–3.7 cm long in middle of cyme, spine-tipped and with 15–28 large and small teeth per side, longest 8–12 mm, small teeth inserted on large, teeth with scattered hairs near base only, less than 1 mm long; bracteoles lanceolate to obovate, 3.2–3.8 cm long, toothed in apical ½–3/4 with up to 25 teeth per side.

Morphology Reproductive morphology Flowers Calyx

Calyx green with purple apical part and teeth and yellow thickened part, sparsely to densely sericeous-pubescent; dorsal sepal 1–3-veined, ovate with long parallel-sided apical part, 3.5–4 cm long, acute, with 3–20 lateral teeth per side, longest tooth 3–5 mm long, ventral sepal 2-veined, obovate, 3.4–3.8 cm long, with 2 triangular lobes which are acute or 2–4-toothed and ± 8 mm long, with 6–17 lateral teeth per side, longest tooth ± 6 mm long, lateral sepals 1-veined, ovate-elliptic, 2.2–2.7 cm long, acuminate, without or with up to 12 lateral teeth per side (one side often with more than the other).

Morphology Reproductive morphology Flowers Corolla

Corolla tube white, limb deep purple; tube 6–7 mm long below thickened rim which is 8–10 mm long and deeply split dorsally; limb deflexed, 4–5.5 × 3–3.5 cm, finely and sparsely puberulous above and below; callus with broad central groove and two narrow lateral ridges.

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filaments 2.7–3.3 cm long, glabrous; anthers, 4–5.5 mm long, with sparse long curly hairs on sides and sessile glands dorsally.

Morphology Reproductive morphology Fruits

Capsule ± 3 cm long.

Morphology Reproductive morphology Seeds

Seed (immature) discoid, glabrous, ± 8 × 6 mm.

Distribution

Range: Tanzania. Range: Not known elsewhere Range: Not known elsewhere Flora districts: T7

Ecology

Montane grassland and forest margins, occasionally used as a hedge plant; 2000–2300 m

Note

Clearly related to A. polystachius but with a much larger differently coloured corolla and with different bracts and calyx.