18. Costus maboumiensis Pellegr. — Plate 3f; Map 12 Costus maboumiensis Pellegr. (1929) 220. — Type: Le Testu 1820 (holo P; iso BM 2 sheets, BR, MO, P 2 sheets), Gabon, Nyanga, Tchibanga area, ‘ Mayombe bavili, campement de la Maboumi’, 27 Oct. 1914. Terrestrial herb 1–2.6 m tall. Leaves many; sheaths 0.7–2 cm diam; shoots reddish, sheaths green with reddish margin, ligule chartaceous, truncate to 2-lobed, 5–20 mm long; petiole 2–10 mm long, tinged with reddish brown; sheaths, ligule and petiole glabrous; lamina narrowly elliptic, sometimes narrowly obovate, 15–30 by 5–10.5 cm, glabrous on both sides, base acute, the very base sometimes obtuse to cordate, apex acuminate (acu- men 15–40 mm long). Inflorescence many-flowered, ovoid to subglobose, 4–10 by 3–4.5 cm, terminating a separate leafless shoot 20–50 cm long; bracts, appendages of bracts, bracteoles, calyx and ovary glabrous. Flowers 1 per bract; bracts somewhat bulging, pale to bright green, sometimes with narrow dark red margin, coriaceous, ovate to broadly ovate, 2–2.5 by 1–2 cm, callus green to yellow, generally present, 1–2 mm long; appendages absent or present, green, horizontally spreading, ovate-triangular, 1–4 by 2.5–3.5 cm; bracteole boat-shaped, 23–25 mm long, callus whitish, 2–4 mm long; calyx pale green to white, 12–20 mm long, lobes broadly ovate-triangular, 3–5 mm long, callus absent or present and then <1 mm long; co- rolla hyaline, reddish brown to purplish grey to white, 40–50 mm long, glabrous, tube 15–20 mm long, lobes with dark red margins, narrowly ovate, 30–35 mm long; labellum at the outer basal part whitish, outer upper part reddish brown to purplish grey, inner side white with yellow to white central nectar guide and brown purplish-striped lateral parts, funnel-shaped, broadly obovate when spread out, 35–40 by 35–40 mm, margin crenu- late; stamen white, c. 30 by 10 mm, apex white with narrow pink margin, anther 8 –10 mm long. Capsule and seeds not seen. Distribution — Central Africa (Gabon). Habitat & Ecology — In primary or secondary rainforest. At elevations of 0– 530 m. Flowering and fruiting: October and November. IUCN Conservation Status — Costus maboumiensis has an AOO of 36 km 2 and occurs in five locations (we consider the southern and northern Doudou Mountains as two locations) of which only one partly has a protected status, while the others are in areas with more or less logging pressure. We assess the species as Endangered (EN) B2ab(ii,iii). Notes — Costus maboumiensis is recognizable by a combi- nation of the following characters: inflorescence terminating a separate shoot covered with reddish brown sheaths and reddish brown flowers, a colour never seen in any other African species. Furthermore all parts of the plant lack indument. Costus maboumiensis shares with C. dubius a basal inflorescence, but strongly differs by the colour of the flowers, which are dark reddish brown in C. maboumiensis and white in C. dubius.

Published as part of Kamer 1, H. Maas-van de, Maas 1, P. J. M., Wieringa 1, J. J. & Specht, C. D., 2016, Monograph of African Costaceae, pp. 280-318 in Blumea 61 (3) on pages 307-308, DOI: 10.3767/000651916X694445, http://zenodo.org/record/7570023