Costus nimba H.Maas & Maas, 2016

Kamer 1, H. Maas-van de, Maas 1, P. J. M., Wieringa 1, J. J. & Specht, C. D., 2016, Monograph of African Costaceae, Blumea 61 (3), pp. 280-318 : 309

20. Costus nimba H.Maas & Maas , sp. nov. — Plate 4b, d ; Map 12

Costus nimba is characterized by the dense brown indument of its vegeta- tive parts, an inflorescence on a relatively long separate leafless shoot, green bracts and white to salmon pink flowers with a horizontally flattened labellum. —

Type: Phillipson 6415 (holo WAG 2 sheets; iso MO, P), Guinea, Nzérékoré, Nimba Mountains , lower Zié Valley , at edge of World Heritage Site , along river bank in sandy soil, 591 m, 10 July 2012 .

Terrestrial herb 1.5–2.5 m tall. Leaves many; sheaths, 0.8–2.5 cm diam; ligule chartaceous, obliquely truncate to slightly unequally 2-lobed, 14–23 mm long; petiole 13–33 mm long; sheaths, ligule and petiole densely to very densely covered with erect, brown hairs 1–2 mm long; lamina chartaceous, narrowly obovate to narrowly elliptic, 24–36 by 6–10 cm, upper side glabrous except for the midrib, lower side and midrib on upper side (very) densely covered with appressed hairs 1–1.5 mm long, base acute, apex acute to acuminate (acumen 15–20 mm long). Inflorescence many-flowered, ovoid-ellipsoid to cylindric, 10–17 by 4–5.5 cm, terminating the leafy shoot or terminating a separate leafless shoot 24–30 cm long; bracts, bracteoles, calyx, ovary and capsule glabrous. Flowers 1 per bract; bracts green, coriaceous, broadly ovate, 3–3.5 by 2.5–3.5 cm, callus indistinct; appendages absent; bracteole boat-shaped, 30–35 mm long, callus present, 2–4 mm long; calyx 18–22 mm long, lobes broadly ovate-triangular, 4–6 mm long, callus 1–2 mm long; corolla hyaline, salmon-coloured, 40–60 mm long, gla- brous, tube 15–20 mm long, lobes narrowly obovate-elliptic, 25–35(–40) long; labellum at the outer side white, inner side white to very pale salmon pink with pale yellow nectar guide and two dark pink basal zones covered with erect hairs c. 1.5 mm long, horizontally flattened, depressed obovate when spread out, 40–45 by 40–45 mm, margin crenulate; stamen white, c. 30 by 12–18 mm, anther 7–8 mm long, apex acute. Capsule ellipsoid to obovoid, 14–17 by 8–11 mm. Seeds c. 2 by 1 mm.

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

Habitat & Ecology — In rain f orest along river bank, in sandy soil, at elevations of 0–1150 m. Flowering and fruiting: May to December.

Field observations — The flowers of C. nimba emit a ‘fragile sweet scent’ (Jongkind & Bilivogui 11301).

IUCN Conservation Status — Least Concern.

Additional specimens examined. CAMEROON, South Province, Djoum, 600 m, anno 2014, Cheek 17660 ( K, WAG, YA) . South-West Province, Mondemba-Fabe Road, 22 Nov. 1986, Nemba & Thomas 331 ( K, WAG). –

GHANA, Brong-Ahafo Region, between Wenchi and Bamboi, 350 m, 3 Oct. 1996 , Jongkind 3138 ( WAG) . Eastern Region, Kade, 2 June 1968, Hall GC 38519 ( GC, K) ; Busoso-Begoso Road, 16 June 1969, Hossain & Enti GC 35403 ( GC) ; ‘Ex Garden Legon, original from Kade’, 18 Dec. 1956, Morton GC 8334 = P 2051 ( GC) ; Kwahu West District,Akoase, 196 m, 8 July 2010, Van Andel et al. 5735 ( WAG) . – GUINEA, Nzérékoré, Nimba Mts, Zié Valley, 590 m, 21 Sept. 2011, Jongkind & Bilivogui 11163A ( WAG) ; Nimba Mts, Zié River, 667 m, 10 July 2012, Jongkind & Bilivogui 11301 ( BRLU, WAG) ; Nimba Mts, inside the WHS site close to the Zié River bridge, 540 m, 28 Oct. 2012 , Jongkind et al. 11620 ( WAG) . – IVORY COAST, Divo, between Divo and Lakota, 18 Apr. 1968, Aké Assi 10030 ( G) ; Divo, 5 km SE of Guitry, 20 m, 1 Nov. 1975, Beentje 1283 ( WAG) ; Forêt de Divo, 10 Aug. 1975, Hall & Abbiw GC 45357 ( GC) . Guiglo , Taí, between Sakré and Nigré, 28 Dec. 1987, Aké Assi 17871 ( G) . Man , Man, near climatic station on Mt Tonkoui, 1150 m, 28 May 1975, Beentje 341 ( WAG) . Soubré, Haut Sassandra, Pays des Byolas, entrée du village de Dyedeougou, 10 May 1909, Chevalier 21517 ( P) . – LIBERIA, Eastern Province , Webo District,Sarbo, 6 July 1947, Baldwin Jr. 6410a! ( K) . – SIERRA LEONE, Northern Province, 15 miles N of Port Loko, in garden at FBC, 28 Apr. 1965, Morton s.n. ( K) . Southern Province, near Mokebi (Kori), 26 May 1953 , Jordan 900 ( K) ; without location, 1915, Thomas 8455 ( K) .

Notes — Costus nimba comes closest to C. dubius , both sharing a basal inflorescence with green, unappendaged bracts. It differs, however, by the dense brown indument of its vegetative parts (absent in C. dubius ), its horizontally flattened labellum with two basal salmon pink patches and yellow nectar guide (funnel-shaped with yellow nectar guide in C. dubius ) and its hyaline salmon pink corolla lobes (white and not hyaline in C. dubius ). Costus nimba differs from C. dinklagei , another species having a basal inflorescence with green, unappendaged bracts and hyaline corolla lobes by its salmon pink corolla lobes (whitish in C. dinklagei ), by its horizontally flattened white labellum with two basal salmon pink patches and yellow nectar guide (pale pink, funnel-shaped with yellow nectar guide in C. dinklagei ) and its generally larger inflorescence and a longer separate leafless shoot.

Figures

Plate 4 a. Costus macranthus K.Schum. Habit, flower and details of stamen, stigma and style. – b. Costus nimba H.Maas & Maas. Basal inflorescence. – c. Costus spectabilis (Fenzl) K.Schum.Habit with flowers. – d. Costus lucanusianus J.Braun & K.Schum. Inflorescence with 4 flowers.– e. Costus talbottii Ridl. Flower. – f. Costus louisii H.Maas & Maas. Inflorescence (a: Wright 1905: t 7992; b: Jongkind 11301; c: photographed in Rumonge, SW Burundi, no specimen collected; d: Maas et al. 10000; e: Maas et al. 9800; f: Maas et al. 10339). — Photos: a, b, d–f: P.J.M.Maas; c: E. Fischer.

Map 12 Distribution of Costus maboumiensis Pellegr. (■) and C. nimba H.Maas & Maas (●).