Costus L., Sp. Pl. 1: 2. 1753; Fl. China @ eFloras.org 24: 320; Lock, Fl. Trop. East Afr. 1985.

Rhizomatous perennial herb, mostly terrestrial, rhizomes horizontal, tuberous. Leafy stems erect, straight or spirally contorted. Leaves arranged in an open continuous spiral (spiromonostichous), with sheathing bases, sheaths closed, smooth; ligule present and often prominent, completely encircling the stem (sometimes incorrectly called ochrea); base of lamina contracted into a pseudopetiole; leaf blade of lower leaves reduced, upper ones ovate to obovate, pubescent or glabrous. Inflorescences terminal or lateral on separate short leafless shoots arising from rhizomes, conical, densely many-flowered; bracts imbricate, 1-2-flowered. Flowers large, bisexual, strongly zygomorphic, each subtended by a bracteole (if 2 flowers are present, one bracteole may be rudimentary). Calyx tubular, with 3 apical teeth or lobes, sometimes split to the base on one side. Petals 3, all similar or posterior a little larger than the laterals; basal 1/3rd of petals and base of androecium fused to form a tube. Androecium consisting of one fertile stamen and one staminode (labellum); labellum very broad and petaloid, usually elliptic, entire; anther subterminal, anther thecae linear. Ovary 3-locular, ovules many per loculus, nectaries embedded in the apex of ovary; style filiform, passing through anther thecae; stigma funnel-shaped with a ciliate margin and a dorsal appendage. Fruit a berry or subglobose woody capsule crowned with persistent calyx. Seeds many, black, arillate.

97 species

Costus pictus D. Don, Edward’s Bot. Reg. 19: t. 1594. 1833; keralaplants.in; Flora de Nicaragua.

Perennial rhizomatous herb. Leafy shoots ca. 1 m tall. Leafy stems erect, usually spirally contorted, mostly unbranched, reddish, with conspicuous nodes and internodes. Leaves arranged in an open continuous spiral (spiromonostichous) with sheathing bases, sheaths closed, smooth, up to 5.5 cm long; ligule prominent, 2-3 mm long, shallowly 2-lobed, reddish-green, completely encircling the stem ( sometimes incorrectly called ochrea), margin shortly or longly ciliate; base of lamina contracted into a pseudopetiole, 2-3 cm long, glabrous, green; lamina rolled longitudinally in bud, lamina of lower leaves absent (only leaf sheath present), upper ones ovate, ovate-elliptic to obovate, 7-16 cm x 3.5- 5.5 cm, margin entire or ciliate, apex acuminate, base usually cuneate, sometimes subcordate, midrib prominent, venation pinnately parallel, both surfaces green, mostly glabrous, rarely puberulent abaxially. Inflorescences terminal on leafy shoots, conical, globose to ovoid compact spikes, 3-8 cm x 3-4 cm, many-flowered, mostly one flower opened at a time; bracts many, closely imbricate, ca. 3.8 cm x 3.5 cm, broadly ovate, greenish towards apex, reddish-brown towards base, coriaceous, 1 flower per bract. Flowers large, ca. 6 cm long, bisexual, epigynous, strongly zygomorphic, each subtended by boat-shaped reddish-brown bracteole, ca. 2 cm x 1 cm. Pedicel short, puberulous. Calyx 7-8 mm long, tubular, reddish-brown, 3-lobed, pubescent, persistent. Corolla lemon-yellow, glabrous; petals 3, connate at base, ca. 4 cm x 2 cm, broadly ovate, margin recurved; lateral lobes ca. 4 cm x 1.2 cm, ovate-oblong. Androecium consisting of 1 staminode (labellum) and 1 fertile stamen, fused at base with corolla tube. Labellum 4-6 cm long, petaloid, showy, funnel-shaped; basal part tubular, lemon-yellow; apex 3-lobed, mid lobe yellow without stripes, lateral lobes light yellow with reddish-brown stripes. Fertile stamen free, petaloid; filament 2 cm x 1 cm, yellow, usually elliptic, entire, hairy towards centre; anther subterminal, anther thecae linear, 6 mm x 4 mm, whitish grey, dehiscence by longitudinal slits. Ovary inferior, hirsute, 6 mm x 3 mm, trigonous, 3-locular, ovules many per loculus; style filiform passing through the anther thecae; stigma funnel-shaped with ciliate margin and a dorsal appendage.

Fruit subglobose capsule with persistent calyx, up to 1.5 cm in diameter. Seeds many, black, arillate. (Fruits not observed)

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