Costus albiflos 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 : 293

3. Costus albiflos Maas & H.Maas , sp. nov. — Plate 1c; Map 2

Costus albiflos is very easily recognizable by its leafless flowering shoot, green appendaged bracts and completely white flowers (with only a slightly yellow nectar guide). Its petiole, ligule and sheaths are covered with appressed, 0.5–1 mm long hairs with a thickened base creating a ‘rough’ feeling. — Type: Maas et al. 10411 (holo WAG 2 sheets [WAG0380170, WAG0380171];iso BR,K, L [L.2079937],LBV,MO,P, UC), Gabon, Estuaire, side road at km 46 of road from Kougouleu to Méla , on the border of Parc National Monts de Cristal , 15 m, 21 Nov. 2011 .

Terrestrial herb 1–3 m tall. Leaves many; sheaths 1–1.5 cm diam; ligule chartaceous, 2-lobed, 10–30 mm long; petiole 5–10 mm long; sheaths, ligule and petiole rather densely covered with appressed hairs <1 mm long; lamina pale green below, narrowly elliptic to narrowly obovate, 20–40 by 5–8 cm, slightly 6 –10-plicate, upper side glabrous or sparsely covered with appressed hairs <1 mm long, lower side sparsely covered with appressed hairs <1 mm long to glabrous, midrib rather densely so and hairs longer, base acute, apex acuminate (acumen 15–20 mm long). Inflorescence many-flowered, ovoid, 4–12 by 3–8 cm, terminating a separate leafless shoot 10–50 cm long; bracts, appendages of bracts, bracteoles and calyx sparsely covered with appressed hairs <1 mm long, ovary and capsule glabrous. Flowers 1 per bract; bracts green, coriaceous, broadly ovate, 1.5–2 by 1–2.5 cm, callus absent; appendages green, horizontally spreading, broadly ovate-triangular to ovate-triangular, 1–3.5 by 1–2.5 cm; bracteole boat-shaped, 18–20(–25) mm long, with 1 or 2 calli 1–1.5 mm long; calyx 9–14 mm long, lobes ovate-triangular, 2–4 mm long, callus absent; corolla white, 50–55 mm long, glabrous, tube c. 15 mm long, lobes narrowly ovate, 35–40 mm long; labellum white, inner side sometimes with a pale yellow nectar guide, horizontally flattened, broadly obovate when spread out, 30–35 by 30 mm; stamen white, 30–40 by 10 mm, anther 5–6(–9) mm long. Capsule ellipsoid, 10–15 by 6–8 mm. Seeds 1–2 by 1–2 mm.

Distribution — Central Africa ( Cameroon, Gabon).

Habitat & Ecology — In lowland rainforest, often near streams, at elevations of 0–700 m. Flowering and fruiting: February, April and May.

IUCN Conservation Status — Based on an AOO of 40 km 2 from seven locations of which only one is part of a National Park, while most others face several logging threats, we assess this species as Vulnerable (VU): B2ab(ii,iii,iv).

Other specimens examined. CAMEROON, South Province, Collines BOG, 5 km W of Atogboga (25 km NNE of Bipindi ), 30 Jan. 1974, Letouzey 12829 (P) ; Colline Nkol Tsia, 18 km NW of Bipindi, near Gouap , 488 m, 5 Feb. 1974, Letouzey 12913 (P) ; Nyangong , transect 8, 700 m, 12 Dec. 1996, Van Gemerden 101 ( WAG) . South-West Province, Ndian, Ekundu Kundu , 200 m, 26 Apr.1996, Cheek et al.8204 (K, WAG) .– GABON, Estuaire, Crystal Mountains, 3 km along track Alen Nkomo-Andok Foula , 30 m, 21 Nov.1986, J.J.F.E. de Wilde et al.8895 (LBV, MO, WAG) ; Parc National de Monts de Cristal, road L108 from Kinguélé to Tchimbélé , past Kinguélé , c. 300 m, 24 Oct. 2011, Maas et al. 9968 ( LBV, WAG) . Woleu-Ntem, Chantier Oveng ,c. 500 m, 7 May 1986, A.M. Louis 2185 ( LBV, WAG) ; Crystal Mountains , 1 km S of Tchimbélé, 450 m, 14 Nov. 2004, Wieringa et al. 5423 ( WAG) .