Vanilla imperialis Kraenzl., Notizbl. Königl. Bot. Gart. Berlin 1: 155 (1896).
Vanilla lujae De Wild., Belgique Colon. 10: 28 (1904).
Vanilla imperialis var. congolensis De Wild., Rev. Hist. Nat. Appl. 2: 188 (1921).
Vanilla grandifolia var. lujae (De Wild.) Geerinck, Bull. Soc. Roy. Bot. Belgique 107: 58 (1974).
Type: Cameroon, Yaounde, Zenker & Staudt 626 (holotype Bt).
A climbing vine up to 20 m or more in length. Stems succulent, cylindrical, longitudinally shallowly grooved, internodes up to 15 cm long, 2- 2.5 cm in diameter. Leaves fleshy-succulent, broadly elliptic oblong to ovate, apiculate, 15 - 25 cm long, 8 - 12 cm broad, dull bluish green; roots bootlace-like, grey, emerging opposite the leaves at the nodes.
Inflorescences lateral from the axils of the upper leaves, sessile, densely many-flowered with the flowers emerging in succession, unbranched, up to 15 cm long; bracts ovate, obtuse or subacute, 1.5 - 3 cm long. Flowers not opening widely, lasting 1 - 2 days, yellow to creamy yellow with a heavily maroon blotched lip; pedicel and ovary up to 11 cm long. Sepals elliptic-lanceolate, acute, 7 - 8 cm long, 1.4 - 8 cm wide. Petals similar. Lip funnel-shaped, up to 6 cm in length, basally united to the column almost to the anther, hairy in tube; side lobes broadly rounded and enclosing the column apex; midlobe acute, long papillate towards the apex, margin crenulated; callus a dense tuft of fine hairs. Column arcuate, subclavate, up to 4 cm long, hairy on ventral surface. Capsule cylindrical, bean-like, up to 25 cm in length and 1.5 cm in diameter, green.
In forest, scrambling up trees in shade, 900-1200 m.
Vanilla imperialis is the largest orchid in tropical Africa but can easily be overlooked because the vines resemble some Araceae and flowering occurs usually in the canopy of forest trees. Found throughout tropical Africa from Sierra Leone and the Ivory Coast to Angola and Tanzania, Hunt (1984) reported it from neighbouring Uganda where it occurs between 900 - 1200 m elevation in forested regions of Bunyoro, Mengo and Masaka Districts. Its occurrence in Ethiopia, well to the north, is therefore something of a surprise. However, it can scarcely be mistaken for any other tropical African species being larger in its habit and in having distinctively coloured flowers.
Angola, Cameroon, Ghana, Ivory Coast, Sierra Leone, Tanzania, Uganda, Zaire.