Costus gabonensis Koechlin — Plate, 1964

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 : 296-299

8. Costus gabonensis Koechlin — Plate 2b; Map 7

Costus gabonensis Koechlin (1964) 82, pl. 18, 1–5. — Type: Le Testu 2240 (holo P; iso A, B, BM, BR, G, K, L [L.1480436], P), Gabon, Ngounié, Tsamba, 27 Oct. 1917.

Terrestrial herb 0.5–2.5 m tall. Leaves several; sheaths 0.5–1 cm diam; ligule membranous, 2-lobed, 5–35 mm long; petiole 2–5 mm long; sheaths, ligule and petiole densely to sparsely covered with erect hairs to c. 5 mm long; lamina green, sometimes purple-red at lower side, shiny at upper side, narrowly elliptic, 13–28 by 5–9 cm, upper side covered with stiff, erect hairs 1.5–2 mm long to glabrous, lower side sparsely to rather densely covered with soft erect hairs c. 1.5 mm long, base acute, obtuse to subcordate, apex acuminate (acumen 5–10 mm long). Inflorescence many-flowered, ellipsoid to ovoid, 5–9 by 2–4 cm, terminating a leafy shoot; bracts, appendages of bracts, bracteoles, calyx, ovary and capsule densely to rather densely covered with erect to appressed, white hairs <1 mm long. Flowers 1 per bract; bracts white at base, greenish pink

Fig. 4 Costus fenestralis Maas & H.Maas a. Habit showing few leaves in an apical rosette; b. detail of sheaths dilacerating into fibers; c. detail of withered bract; d. detail of bracteole and calyx; e. inflorescence (all: Jongkind et al. 5811, WAG). — Drawing by Hendrik Rypkema.

to red or purplish brown at apex, chartaceous, broadly obovate to obovate, 1–1.5 by 0.5–1.5 cm, callus absent; appendages pinkish red to purplish brown, strongly reflexed, narrowly triangular to triangular, 1–3 by 0.6–1.5 cm; bracteole boat-shaped 15–20 mm long, callus green, 1–3 mm long; calyx 9–10 mm long, lobes deltate to very shallowly triangular, 1.5–3 mm long, callus absent; corolla yellow to dark yellow, 40–50 mm long, densely to rather densely covered with (erect to) appressed, white hairs <1 mm long, tube 10–20 mm long, lobes narrowly elliptic, 20–30(–40) mm long; labellum completely yellow, horizontally flattened, broadly obovate when spread out, 35–50 by 40–50 mm, margin irregularly lobed; stamen yellow, 35–40 by 7–10 mm, apex slightly orange, anther 7–8 mm long. Capsule obovoid, 9–10 by 6–7 mm. Seeds c. 3 by 2 mm.

Distribution — Central Africa ( Gabon).

Habitat & Ecology — In primary and secondary rainforest, at elevations of 300–1000 m. Flowering and fruiting: September to December.

Field observations — The flowers of this species are quite aberrant from any other species of Costus in that they emit a strong scent reminiscent of jasmine (A.M. Louis et al. 853, Van Valkenburg et al. 2649).

IUCN Conservation Status — Based on an AOO of 88 km 2 from about 14 locations of which only two are located in a protected area, while the others are located in areas currently being logged or face logging threats, we assess this species as Near Threatened (NT).

Plate 2 a. Costus dubius (Afzel.) K.Schum. Basal inflorescence. – b. Costus gabonensis Koechlin. Inflorescence. – c. Costus giganteus Welw. ex Ridl. Inflorescence. – d. Costus gracillimus Maas & H.Maas. Inflorescence with red bracts (a: photographed in Burgers’ Bush,Arnhem, The Netherlands, no specimen collected; b: Maas et al. 10465; c: Scharf 221; d: Maas et al. 10571). — Photos: a, b, d: P.J.M.Maas; c: L.Y.T.Westra.

Notes — Costus gabonenis is unique by its combination of bracts with reflexed red to purplish brown appendages, yellow flowers and a densely hairy corolla. It is endemic to Gabon and it superficially resembles the Neotropical C. comosus (Jacq.) Roscoe.

The boat-shaped bracteole of C. gabonensis is 2-keeled to almost 2-winged presumably caused by the compactness of the inflorescence. The base of the shoot is red or purplish brown.