Costus gracillimus Maas & H.Maas, 2016

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 : 299-300

10. Costus gracillimus Maas & H.Maas , nom. nov. — Plate 2d; Map 6

Costus gracillimus Maas & H.Maas. — Costus pulcherrimus A.Chev. (1917) 304, nom. illeg., non Kuntze (1898) 301. — Type: Chevalier 19568 (holo P), Ivory Coast, Tabou , ‘ Bassin du Cavally, pays des Tépos, entre Toula et Nekaougnié’, 25 July 1907.

Terrestrial herb 1–3 m tall. Leaves many; sheaths 0.2–0.6 cm diam; ligule chartaceous, obliquely truncate, 10–15(–20) mm long; petiole 5–10 mm long; sheaths, ligule and petiole glabrous or rarely sparsely covered with erect hairs <1 mm long; lamina greyish to brown on upper side, lower side paler, coriaceous, narrowly elliptic to elliptic, 13–21 by 4–8 cm, slightly 4–6-plicate, glabrous on both sides, but margins and apex rarely covered with some hairs, base acute, apex acuminate (acumen 10–15 mm long). Inflorescence few-flowered, broadly ovoid to globose, 1.5–5 by 1.5–5 cm, terminating the leafy shoot; bracts, bracteoles, calyx, ovary and capsule glabrous, rarely rather densely covered with erect hairs <1 mm long. Flowers 1(–2) per bract; bracts red, orange-red to red-purple, coriaceous, broadly ovate to ovate, 1.5–2.5 by 1.5–2.5 cm, callus mostly absent or present and then c. 1 mm long; appendages generally absent; bracteole boat-shaped, 9–14 mm long, callus 1–2 mm long; calyx 7–10 mm long, lobes very shallowly triangular, c. 1 mm long, callus absent; corolla fleshy, 20–29 mm long, red, orange or yellow, glabrous, tube 5–7 mm long, lobes narrowly ovate to elliptic, 15–22 mm long; labellum fleshy, red, orange or yellow, tubular, broadly obovate when spread out, 15–23 by 15–20 mm, margin crenulate; stamen yellow, 13–15 by 6–8 mm, anther 7–8 mm long. Capsule obovoid, 9–10 by 5–6 mm. Seeds 1.5–2 by 1.5 mm.

Distribution — West Africa ( Ghana, Guinea, Ivory Coast, Liberia, Sierra Leone).

Habitat & Ecology — Mostly in rainforest, along paths or in open places and/or disturbed areas, often in wet places, at elevations of 0–850 m. Flowering and fruiting: all year through.

IUCN Conservation Status — Based on all collections C. gracillimus has an AOO of 184 km 2 from about 20 locations of which only four are partially protected, while the remainder of these locations are already lost or face severe habitat degradation. If we only use records collected since 1970, this species has only 10 locations left (with an AOO of 68 km 2), of which the majority is lost or threatened. We therefore assess this species as Vulnerable (VU) A2; B2ab(i,ii,iii,iv,v).

Notes — Costus gracillimus is a relatively small herb with a slender spiralling shoot (0.2–0.6 cm diam), a long ligule (10– 15 mm long) and relatively small, tubular, fleshy flowers. The leaves of C. gracillimus have relatively narrow and long petioles. The labellum is about as long as the corolla, forming a tube with its longitudinally incurved margins. The majority of plants studied have red bracts with red-orange flowers. However, Jongkind et al. 11941 from Liberia has green bracts and yellow flowers. Based on the overall similarities of this single collection, we do not believe it to be a separate species but rather a lighter-coloured form of C. gracillimus .

Costus gracillimus has often been misidentified as C. deistelii K.Schum. That species, known only from the type collection Deistel 498 (B destroyed), now placed in the synonymy of C. afer , differs from C. gracillimus by a shorter ligule, longer inflorescence and bracteole, and the presence of a rim at the base of the ligule not completely encircling the shoot.