Costus L.

Rhizomatous perennial herbs, terrestrial or (not in E. Africa) epiphytic. Oil cells absent, plant scentless. Leafy stems usually erect and several m. tall, but occasionally very short or creeping. Leaves usually arranged in an open spiral (spiromonostichous), with sheathing bases, rarely in a rosette or (not in E. Africa) solitary; sheaths closed, smooth; ligule present and often prominent, encircling the stem (and sometimes, therefore, incorrectly called an ochrea); base of lamina contracted into a pseudopetiole; lamina of lower leaves reduced, upper ones ovate to obovate, variously pubescent or glabrous; hairs often bicellular. Inflorescences usually condensed into subglobose cone-like spikes, either on specialised bracteate shoots arising from the rhizome, separate from the leafy shoots, or terminating the leafy shoots (both conditions may be found in a single species), or (not in E. Africa) lateral on the leafy shoots. Flowers large, strongly zygomorphic, 1-2 together in the axil of each bract, each subtended by a bracteole (if 2 flowers are present, one may be rudimentary). Calyx tubular, with 3 apical teeth, sometimes split to the base at one side. Petals 3, all similar, or the posterior a little larger than the laterals; basal third of the petals, and the base of the androecium fused to form a tube. Androecium consisting of 1 broad petaloid staminode (the labellum) and a single free stamen; free stamen petaloid, usually elliptic, entire; anther subterminal. Labellum very broad and petaloid, variously coloured, curved into a funnel-shaped structure. Style filiform, passing between the anther-thecae and ending in a funnel-shaped stigma with a ciliate margin and a dorsal appendage. Nectaries embedded in the apex of the ovary. Fruit a berry, probably indehiscent (but dehiscent in the South American species), usually remaining covered by the bracts (which open out in fruit in some South American species), crowned by the persistent calyx. Seeds hard, blackish, arillate.