Costus afer Ker Gawl. — Plate, 1823

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 : 290-293

2. Costus afer Ker Gawl. — Plate 1a; Map 3

Costus afer Ker Gawl. (1823) t. 683; K.Schum. (1904) 392. — Type: A specimen from cultivated material in the greenhouses of the Horticultural Society at London (Chelsea) from material collected in Sierra Leone by G. Don (holo CGE).

Costus sarmentosus Bojer (1835) 262, t. 8; K.Schum. (1904) 394, syn. nov. — Type (lectotype selected by Lock (1985: 7): Bojer (1835) plate 8, drawn from a plant from Zanzibar.

Costus trachyphyllus K.Schum. (1892) 420; (1904) 409, syn. nov. — Type: Schweinfurth ser. III, n. 206 (lecto K, selected by Lock (1984) 842), Congo Kinshasa, Orientale, Mbrwole River (‘bei Mruole am Nabambisso’ ), 1 Mar. 1870.

Costus edulis De Wild.& T.Durand in Durand & De Wildeman (1899) 141. — Type: Dewèvre 916a (holo BR), Congo Kinshasa, Nyangwe, Mossungulore , anno 1896.

Costus oblitterans K.Schum. (1904) 393, syn. nov. — Syntypes: Unknown collector s.n. (B destroyed), Ghana (‘Goldcoast’), without location; Millen s.n. (B destroyed), Nigeria, Lagos .

Costus deistelii K.Schum. (1904) 393, syn.nov. — Type: Deistel 498 (holo B destroyed), Cameroon, South-West Province, Buea , Feb. 1900.

Costus subbiflorus K.Schum.(1904) 394,syn.nov. — Type: Volkens 50 (B destroyed;lecto BM, designated here), Tanzania, Lushoto Distr. , ‘ Usambara , von Derema bis Magila (‘Msassaberg’), häufig im Urwald z. B. bei Punga Ninga’ , 900 m, 21 Jan. 1893; other syntypes: Engler 715 (B destroyed), Tanzania, ‘ Usambara’, Amani , 800–900 m, Nov. 1902 ; Buchwald 360 (B destroyed), Tanzania, ‘ Usambara’, Mt Lutindi between Kwa Mburaka and Kisula, 19 Jan. 1896 ; Liebusch 17 (B destroyed), Tanzania, ‘ Usambara’, Tanga, Pamota , 800–1000 m, 15 Mar. 1900 .

Costus pterometra K.Schum. (1904) 394, syn. nov. — Type: Schweinfurth III-204 (holo B destroyed;lecto K 2 sheets,designated here), South Sudan, ‘Ghasaquellengebiet, Land der Niamniam am Nabambisso’, 20 Feb.1870.

Costus anomocalyx K.Schum. (1904) 396, syn. nov. — Type: Baumann 8 (holo B destroyed), Togo, ‘ Misahöhe, 496 m ü. M.’, 15 Mar. 1894.

Costus megalobractea K.Schum. (1904) 407, syn. nov. — Type: Braun s.n., anno 1888 (holo B destroyed), Cameroon, South Province, Gross-Batanga.

Costus bingervillensis A.Chev. (1920) 627, syn. nov. — Type: Chevalier 15214 (lecto P, designated here), Ivory Coast, Bingerville region, Abidjan, Dabou, 19 Mar. 1905; other syntypes: Chevalier 17280 (LY, P p.p.), Ivory Coast, Bingerville, 14–18 Dec. 1907; the specimen in P is a mixed collection of C. afer and C. lucanusianus ; Chevalier 19883 (P), Ivory Coast, Tabou, banks of Bas-Cavally, between Prolo and Bliéron, 11 Aug. 1907.

Costus insularis A.Chev. (1920) 627, nom. nud. Based on Chevalier 13058 (P), Guinea, Iles de Los, 25 Feb. 1905.

Terrestrial herb, erect but in fruit sometimes individual shoots bending down, 0.5–4(–5) m tall. Leaves many; sheaths 0.8– 1(–1.5) cm diam; ligule chartaceous, 2-lobed to truncate, (2–) 4–11 mm long, with a basal horizontal rim c. 1 mm high, not completely encircling the shoot, sometimes bearing erect hairs to c. 3 mm long; petiole 5–14 mm long; sheaths, ligule and petiole glabrous to densely covered with erect to half-appressed white hairs <1 mm long; lamina narrowly elliptic to narrowly obovate, 7–25(–40) by (3–)4–10(–19) cm, upper side glabrous, lower side glabrous to rarely midrib densely covered with erect to half-appressed white hairs 1– 2 mm long, margin often with a row of hairs <1 mm long, base cordate to acute, apex acuminate (acumen 15–30 mm long). Inflorescence many-flowered, globose to ellipsoid, (2.5–)4–14(–20) by 2.5–6(–8) cm, terminating the leafy shoot or rarely terminating a separate leafless shoot 10–30 cm long; bracts, appendages of bracts, bracteoles and calyx glabrous, sometimes sparsely to rather densely covered with erect hairs <1 mm long, upper part of capsule densely covered with erect hairs <1 mm long. Flowers (1 or)2 per bract; bracts (pale) green often with reddish upper margin, coriaceous, ovate-triangular to depressed ovate-triangular, 2–3 by 2–2.5 cm, callus 2–3 mm long; appendages rarely present, green, horizontally spreading to reflexed, narrowly triangular, 4–10 by 2.5–3 cm; bracteole boat-shaped, 14–25 mm long, callus 1–4 mm long; calyx 12–19(–22) mm long, lobes broadly ovate-triangular, (2–) 4–5 mm long, erect and sometimes exceeding the bracts in fruit, callus 1–2 mm long; corolla white to yellowish, 30–45 mm long, glabrous, tube 5–10 mm long, lobes (narrowly) elliptic, 20–40 mm long; labellum at the outer side white, inner side white with (pale to dark) pink lateral marginal parts and yellow nectar guide, sometimes completely white with or without yellow nectar guide, funnel-shaped, broadly obovate when spread out, 30–45 by 35–50 mm, margin crenulate; stamen white, 25–40 by 10 mm, apex white, anther 6–9 mm long. Capsule broadly obovoid, to 15(–20) mm diam. Seeds 1–2 mm diam.

Distribution — North East Africa ( Ethiopia, South Sudan); West Africa ( Benin, Burkina Faso, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Nigeria, Senegal, Sierra Leone, Togo); Central Africa ( Burundi, Cameroon, Central African Republic, Congo Brazzaville, Congo Kinshasa, Equatorial Guinea, Gabon, São Tomé & Principe); East Africa ( Kenya, Tanzania, Uganda); Southern Tropical Africa ( Angola, Malawi, Mozambique, Zambia, Zimbabwe).

Habitat & Ecology — In open places like roadsides and forest margins, in secondary or savanna forest, often on wet places, near rivers; on sandy soil and on rocky outcrops, at elevations of 0–1770 m. Flowering and fruiting: all year through.

IUCN Conservation Status — Least Concern.

Notes — Costus afer is characterized by an incomplete horizontal rim around the nodes of the shoot which is covered with only some erect hairs to c. 3 mm long, a 4–11 mm long ligule and erect calyx lobes that are sometimes exceeding the bracts in fruit. The corolla is white, the labellum is white with yellow nectar guide and reddish margins and the stamen is white with reddish apical part.

Costus afer has often been confused with C. dubius , both species sharing green, unappendaged bracts and more or less white flowers, but C. afer is generally characterized by inflorescences terminating leafy shoots and flowers with a white labellum that has a yellow nectar guide and pink margins, while C. dubius generally has inflorescences on short, separate leafless shoots near the base of the plant and white flowers with a labellum bearing a yellow nectar guide but lacking pink margins. The bracts of C. afer are 1- or 2-flowered and sometimes appendaged, those of C. dubius are always 1-flowered and generally not appendaged.

For the differences with C. lucanusianus , a species with which it has been sometimes confused, see under that species.

For the differences with the similar looking C. louisii , see under that species.

The inflorescence of C. afer can terminate a leafy or leafless shoot as is known in many species of Costus ; moreover, plants with 1- and/or 2-flowered bracts can be found all over the distribution area (Maas et al. 10023).

The flower colour of C. afer is often (incorrectly) described on the collection label as ‘white’. This was the case in about 1/4 of the dried specimens included in this study. Indeed the corolla and the outer side of the labellum are white, but the inner side of the labellum is not completely white, but always has more or less reddish margins and a yellow nectar guide. The apical part of the stamen is white to pink.