Acanthus eminens C.B.Clarke

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, Mau, Scott Elliot 6926 (holotype K!; isotype BM!).

Distribution

Sudan (Imatong Mts), Ethiopia, Uganda, Kenya.

Ecology

Primary and disturbed wet evergreen montane (rarely intermediate) forest, forest margins, coffee plantations, persisting in secondary forest, scrub and thicket clumps in wetter areas, often forming large stands, occasionally used as a hedge plant; (950 -) 1500 - 2800 m.

Conservation

Often a dominant element of the undergrowth of montane forest. In the Imatong Mts in the Sudan it forms (pers. obs.) large, almost impenetrable thickets under Podocarpus in the montane forest from 1800 - 2200 m. There are recent collections from all parts of the distribution area. Some of the forest areas where it occurs are exploited to a smaller or larger degree for timber, firewood, building poles and cattle fodder. The species is unpalatable to browsing animals and does not reach dimensions that make it usable for firewood or poles. It is difficult to imagine it becoming threatened in any of its core areas. Least Concern (LC).

Note

The absence of Acanthus eminens from all of northern Kenya and northern Uganda is due to the fact that all of this vast area is covered with dry deciduous Acacia-Commiphora bushland, a vegetation type far too dry to support this species of wet evergreen forests. See also note after A. polystachius. The species could occur on the Uganda side of the Imatong Mts as it is common in the Podocarpus forests on the north side of the mountains, but as yet no specimens have been seen from the south side. See also note after A. seretii.

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

Morphology General Habit

Shrubby herb or shrub to 3 m tall; young stems glabrous.

Morphology Leaves

Leaves with petiole 0.5–2(–2.5) cm long; lamina narrowly elliptic to elliptic or obovate in outline, largest 13–37 × 5–15 cm, deeply lobed with large triangular spine-tipped lobes, each lobe with a spine on antrorse side, apex acuminate to cuspidate, spine-tipped, base attenuate to cuneate, glabrous; each node with one to several persistent sharp terete straw-coloured interpetiolar downwardly directed pungent pale yellow spines to 1.5 cm long, occasionally some with a small lamina.

Morphology Reproductive morphology Inflorescences

Cymes solitary or also 2 from upper leaf-pair, (5–)7–30 cm long; rachis upwards pubescent with hairs and few to many short to long capitate glands, with several pairs of sterile bracts at base, sometimes merging into the vegetative leaves; bracts green to purplish, ovate to elliptic, finely puberulous to sparsely pubescent and upwards with few to many stalked capitate glands, 1.4–2.8 cm long in middle of cyme, spine-tipped and with 4–8 teeth per side (rarely entire); bracteoles subulate to linear, 5–11 mm long, entire.

Morphology Reproductive morphology Flowers Calyx

Calyx green to purplish, puberulous and with few to many stalked capitate glands; dorsal and ventral sepals longer than bract, oblong-obovate, similar or dorsal slightly longer, 2.1–4 cm long, dorsal entire or 2–3-toothed, ventral 2–3-toothed or irregularly toothed, lateral lanceolate, 1.3–2.5 cm long, acuminate.

Morphology Reproductive morphology Flowers Corolla

Corolla dark blue to dark purple (rarely pale blue to almost white); tube 4–5 mm long below thickened rim which is 3–4 mm long; limb 5-lobed, 3.5–5 × 3.5–5 cm, below puberulous with hairs and capitate glands, above glabrous; callus with narrow central groove.

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filaments 1.7–2.2 cm long, glabrous or with stalked glands near apex; anthers 6–9 mm long, densely glandular dorsally.

Morphology Reproductive morphology Fruits

Capsule 2.3–2.5 cm long.

Morphology Reproductive morphology Seeds

Seed ellipsoid to round, 9–10 mm long, glabrous.

Distribution

Range: Uganda. Range: Sudan (Imatong Mts), Ethiopia Range: Kenya. Flora districts: U3 K3 K4 K5 K6 Range: Sudan (Imatong Mts), Ethiopia

Ecology

Primary and disturbed wet evergeen montane forest, forest margins, secondary grassland, often forming large stands, occasionally used as a hedge plant; (1200–)1500–2600 m

Note

Always easily recognised by the spinose nodes and large sepals combined with small bracts. This species must surely also occur in the N Ugandan mountains ( U 1) as it is common in the Imatong Mts on the Sudan side.