COSTACEAE, Nakai, 1941

Maas-van de Kamer, H., Maas, P. J. M., Wieringa, J. J. & Specht, C. D., 2016, Monograph of African Costaceae, Blumea 61 (3), pp. 280-318 : 288-289

KEY TO THE AFRICAN GENERA OF COSTACEAE

1. Plants erect, leaves generally more than two, occasion- ally in a basal rosette; inflorescence many-flowered, bracts conspicuous and often brightly coloured........ Costus

1. Plants prostrate, leaves solitary, never in a basal rosette; inflorescence few-flowered, bracts inconspicuous and not brightly coloured....................... Paracostus

Costus

Costus L. (1753) 2. — Type: Costus arabicus L.

Perennial, rhizomatous herbs, terrestrial or epiphytic, rarely gigantic, tall, low or shootless herbs; shoot erect, unbranched, generally forming a spiral, composed entirely of sheathing leaf bases forming conspicuous nodes and internodes. Leaves few or many, spirally arranged along the shoot; shootless species with few leaves rosulate; leaf sheaths closed around the shoot; ligule present or rarely absent, membranous to chartaceous, tubular at the base and truncate to 2-lobed at the apex, surrounding the shoot above the proximal lobe as a continuation of the sheathing leaf base; petiole present or sometimes absent; lamina generally green, sometimes shiny, or plicate, herbaceous to coriaceous, generally elliptic with acuminate apex and acute base, upper side and lower side with various indument. Inflorescence a many-, several- or few-flowered spike, either terminating the leafy shoot, or terminating a separate leafless shoot, or lateral in the axil of a leaf, ellipsoid to ovoid or globose; bracts spirally arranged, each carrying 1 or 2 flowers, green, red or brownish, membranous, chartaceous or coriaceous, generally ovate to triangular or elliptic, imbricate, callus linear, nectariferous, absent or present; foliaceous appendages absent or present, generally coloured as the bracts, ascending, horizontally spreading or reflexed, broadly ovate to narrowly triangular; each flower enclosed by 1 bracteole, generally coloured as the bracts, boat-shaped or tubular and 1-keeled or sometimes 2-keeled, callus absent or 1 or 2 calli present. Flowers epigynous, perfect, zygomorphic; calyx generally coloured as the bracts, tubular at the base, 2(–3)-lobed, lobes erect, horizontally spreading, or reflexed, callus absent or present; corolla white, yellow, orange, pink, lilac or reddish brown, or a combination of these colours, tubular, 3-lobed, lobes erect, narrowly obovate to elliptic, rarely hyaline; labellum large, longer than or as long as the corolla, white, yellow, orange, pink, lilac, dark red, reddish brown, purple, or a combination of these colours, sometimes with darker lateral parts and/or striped margin and central yellow nectar guide, horizontally flattened, funnel-shaped, or rarely tubular, obovate to subcylindrical when spread out, margin undulate to crenate, sometimes fimbriate; stamen 1, petaloid, generally yellow or white, apex recurved, anther longitudinally placed in the middle, composed of two narrowly elliptic 2-sporangiate thecae; base of stamen and labellum joined into a tube; gynoecium composed of a single ovary, style and stigma; ovary inferior, 3-locular, placentation axile, ovules many, organized in 2 rows, anatropous, septal nectaries 2 at the base of the floral tube; style 1, terminal, cy- lindrical, filamentous, held between the thecae of the anther; stigma 1, 2-lamellate, hooked between the apices of the thecae by a dorsal 2-lobed to rounded appendage. Fruit capsular, 3-locular, generally obovoid, crowned by the persistent calyx, dehiscing loculicidally by three longitudinal slits or indehiscent and irregularly breaking when old. Seeds numerous, black, shiny, irregularly angular; aril white, lacerate.

Distribution — Tropical to subtropical sub-Saharan Africa.

Habitat & Ecology — Along with Marantaceae and Zingiberaceae , Costaceae form a significant part of the understory of the African tropical and subtropical rainforests. All three families form part of important herbaceous communities along forest margins, in forest gaps, and in the regrowth of disturbed forests ( Dhetchuvi 1996).