Acanthus kulalensis 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

Kenya, W.R.Q. & P.A. Luke 10818 (holotypus K!; isotypi BR, CAS, EA, K!).

Morphology General Habit

Shrub to 2.5 m tall; young stems densely puberilous and with scattered longer hairs

Morphology Leaves

Leaves beneath puberulous or densely puberulous on midrib and larger veins, glabrous to puberulous on lamina, above puberulous on midrib, otherwise glabrous or with a few scattered hairs; petiole to 0.7 cm long; lamina ovate to elliptic in outline, largest 10 - 17 x 4 - 7.5 cm, deeply lobed with large triangular spine tipped lobes, each lobe with 1 - 2 spines on both sides; apex acuminate, spine-tipped; base cuneate to truncate; stipule-like interpetiolar leaves present, with lamina up to 0.5 cm long, spiny

Morphology Reproductive morphology Flowers

Flowers in terminal or also axillary (from uppermost axils) racemoid cymes, 3 - 14 cm long; rachis densely sericeous-tomentose, with several pairs of sterile bracts at base; bracts leathery, with 3 - 5 prominent longitudinal veins, straw-coloured, obovate, densely sericeous in basal part, sparsely so upwards, 2.3 - 3 cm long in middle of spike, spine-tipped and with 12 - 25 large and small teeth per side, longest c. 7 mm, small teeth inserted on larger ones near their base, teeth densely hairs, throughout with longest hairs 1 - 2 mm long

Morphology Reproductive morphology Inflorescences Bracteoles

Bracteoles 2, linear-lanceolate, 2.3 - 3.1 cm long, with 5 - 7 teeth per side, longest c. 7 mm long

Morphology Reproductive morphology Flowers Calyx

Calyx divided to base into 4 glumaceous sepals which are thickened and horny at the base, green with purple tips, thickened part yellow, sericeous or densely sericeous with hairs to 3 mm long, conspicuously ciliate; dorsal and ventral sepals ovate or or ovate-elliptic, dorsal 1 - 3-veined, 2.7 - 3.2 cm long, obtuse to acute and spine-tipped or with acuminate 2-toothed tip and with 1 - 8 lateral teeth per side, longest tooth c. 4 mm long, ventral sepal 2 veined, 2.3 - 2.7 cm long, with 2 triangular spine-tipped lobes c. 5 mm long and with 1 - 6 lateral teeth per side, longest tooth c. 3 mm long, lateral sepals 1 veined, ovate, 2 - 2.2 cm long, acuminate, without or with 1 - 2 small teeth per side

Morphology Reproductive morphology Flowers Corolla

Corolla tube white, limb pinkish-mauve; tube apically thickened and spongy and with a dense band of thick retrorse hairs on the inside, 2 - 3 mm long below thickened rim which is 4- 7 mm long and extended dorsally into a 2 - 7 mm long tooth; limb 5-lobed, 3.5 - 5 x 3 - 3.8 cm, below puberulous, above sparsely puberulous; lobes broadly oblong, rounded or central emarginate; 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, 1.8 - 2 cm long, 2 dorsal hairy on inside near base; anthers 1-thecous, oblong, with brushes of stiff hairs along whole length ventrally, 4 - 4.5 mm long, glabrous or with long curly hairs on sides

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary 2-locular with 2 ovules per locule; style linear, glabrous; stigma of 2 linear, acute lobes c. 1.5 mm long.

Distribution

Known only from Mt Kulal in northern Kenya.

Ecology

Grassy glades in dry montane forest and on forest margins; 1975 - 2100 m.

Phenology

Flowering specimens have been collected from July to December.

Conservation

Known only from three collections made within a period of 50 years from the same mountain in NW Kenya. Quentin Luke (pers. comm.) confirms that Acanthus kulalensis is common in the montane grasslands surrounding the dry montane forest on Mt Kulal and also in grassy glades within the forest. The forests on Mt Kulal have been much degraded over the last 25 years particularly by increased grazing and foraging, but the montane grasslands have been much less disturbed. In common with the other species evaluated here A. kulalensis is not palatable to browsing animals and is not used for firewood or building poles. Probably Vulnerable (VU) due to limited area of distribution.

Note

Differs from Acanthus polystachius in the long silky indumentum on bracts and calyx, in the longer bract teeth, in the longer sepals and in having a dorsal tooth on the thickened corolla rim. This last character has not been observed in any other eastern African species. The bract teeth are also differently arranged with the smaller teeth attached on the base of the larger teeth rather than between them.

IUCN Red List of Threatened Species https://www.iucnredlist.org/species/48153858/48154141

Conservation

VU - vulnerable