Costus acutissimus 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 : 290

1. Costus acutissimus Maas & H.Maas , sp. nov. — Fig. 3; Map 2

Costus acutissimus is characterized by narrow leaves with a long-acute apex (hence the specific name),a very short ligule (1–2 mm long),a globose inflorescence (6–8 cm diam) terminating a separate flowering shoot, green appendaged bracts and white flowers with yellow nectar guide. — Type: Van Valkenburg et al. 2768 (holo WAG 3 sheets [WAG0120332, WAG0120333, WAG0120334]; iso BR, LBV [LBV0003152, LBV0003153], MO, P), Gabon, Nyanga, Moukalaba, Doudou National Park, Chantier SFN-Bakker, 250 m, 16 Feb. 2004 .

Terrestrial herb to c. 3 m tall. Leaves many; sheaths 0.5–2 cm diam, falling apart into separate fibers with age and leaving a distinct horizontal rim at the nodes near the base of the shoot; ligule chartaceous, 2-lobed, 1–2 mm long; petiole 1–3 mm long; sheaths, ligule and petiole glabrous to sparsely covered with minute appressed hairs <1 mm long and upper margin of ligule and sheaths with irregular curly fibers to c. 10 mm long; lamina narrowly elliptic, 17–30 by 3.5–7 cm, glabrous on both sides, base obtuse to cordate, apex long-acute to sometimes acuminate (acumen to c. 20 mm long). Inflorescence many-flowered, globose, 6 – 8 by 6– 8 cm, terminating a separate leafless shoot 10–30 cm long; bracts, appendages of bracts, bracteoles, calyx, ovary and capsule sparsely covered with appressed hairs <1 mm long to glabrous; margin of bracts and calyx lobes densely covered with irregular curly fibers c. 1 mm long. Flowers 2 per bract; bracts pale green, chartaceous, broadly ovate-triangular, 2–4 by 2–3 cm, callus absent; appendages green, ascending, broadly ovate-triangular, 1–2 by 1–2 cm; bracteole boat-shaped, 20–25 mm long, callus absent; calyx 25–28 mm long, sometimes split to the base on one side, lobes narrowly triangular, 5–7 mm long, callus absent; corolla white (not seen); labellum white, inner side with yellow nectar guide (not seen); stamen yellow (not seen). Capsule ellipsoid to obovoid, 10–17 by 7–10 mm. Seeds c. 1.5 by 1–1.5 mm.

Distribution — Central Africa ( Cameroon, Gabon).

Habitat & Ecology — In moist valley bottom and on steep hill side. At elevations of 250–500 m. Flowering and fruiting: February, May.

IUCN Conservation Status — Based on an AOO of only 8 km 2 in two quite disjunct locations that both are part of National Parks, we assess this species as Vulnerable (VU): D2.

Other specimen examined. CAMEROON, South-West Province, S of Esukutang , 300–500 m, 25 May 1988, Thomas et al. 7938 ( MO) .

Note — Young shoots of C. acutissimus often show swollen nodes and small bulbils in the upper part of the shoot ( Fig. 3b). Old shoots have distinct horizontal rims of c. 1 mm high, presumably remnants of withered sheaths ( Fig. 3a).