Aerangis jacksonii J.Stewart, Bot. Mag. 182: t. 754 (1978).
Description:
Epiphytic herb; stem woody, up to 20 cm in height, 10 mm diam., bearing 8-15 leaves distributed over its entire length and 6 mm apart; roots numerous, greyish coloured, 3-4 mm diam. Leaves distichous, often falcate, ligulate, linear-lanceolate or oblanceolate, gradually narrowed to the sheathing base, up to 15 x 1-2-3 cm, dark green, black-dotted on both surfaces, the apex unequally bilobed, the lobes obtuse or subacute, the longer one up to 10 mm long, the shorter often absent, margins entire. Inflorescences arising opposite to a leaf, from the same place in several successive years, horizontal or arching racemes bearing 4-8 flowers, up to 17 cm long; peduncle terete, up to 4 cm long, 2 mm diam., pale greenish brown, black-dotted; rhachis - straight; bracts broadly ovate, 5-6 mm long, black at flowering time. Flowers white with a greenish or orange pink suffusion, 8-18 mm apart, opening at the base of the inflorescence first; pedicel with ovary greenish or brownish, 3 cm long. Dorsal sepal erect, narrowly elliptic, acute, 10-12 x 5 mm. Lateral sepals reflexed, narrowly elliptic, 12-15 x 4 mm. Petals reflexed, narrowly elliptic, acute 11-13 x 4 mm. Lip narrowly obovate, the lateral margins reflexed, apiculate, 13-15 x 5 mm; spur deflexed or curving forwards slightly, somewhat thickened in the lower half but tapering towards the tip which is sometimes minutely bicuspidate, 4-5-5 cm long. Column 4 mm high, terete below, widened above; anther cap beaked; rostellum curving downwards, across the face of the stigma; pollinia globose; stipes slender; viscidium obovate; stigmatic cavity rhomboid.
Etymology:
This species is named in memory of the collector, the late T. H. E. Jackson, who bequeathed a fine series of living orchid plants of African epiphytic species to Kew.
Habitat:
Rainforest: 1200-1600 m.
Cultivation:
As given for the genus.
Notes:
The nearest relatives of Aerangis jacksonii appear to be two other species that were first described from Uganda but are now known to be much more widely distributed. The elongated stem and its many rather falcate, linear- oblanceolate leaves somewhat resemble those of Aerangis ugandensis Summerhayes but the new species has much larger flowers. An interesting feature of plants grown under optimum conditions is that several inflorescences arise from the same point, opposite a leaf, in consecutive years, as they so often do in the related genus Diaphananthe. The flowers are rather similar to and only slightly smaller than those of Aerangis collum-cygni but both the column and the nectariferous spur are significantly shorter than in that species.
Distribution:
Uganda
References:
Flora of Tropical East Africa Orchidaceae Part 3 Cribb 1989; African Orchids in The Wild and Cultivation La Croix 1997; Angraecoid Orchids Stewart, Hermans, Campbell 2006; A Revision of the African Species of Aerangis (Orchidaceae) Kew Bulletin, Vol. 34, No. 2 (1979), pp. 239-319; WCSP (2017). 'World Checklist of Selected Plant Families. 19.01-2017; http://apps.kew.org/wcsp/
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