Costus fenestralis Maas & H.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 : 296

7. Costus fenestralis Maas & H.Maas , sp. nov. — Fig. 4 ; Map 6

Costus fenestralis can be recognized by a low number of obovate, densely hairy leaves concentrated at the top of the shoots and bracts soon falling apart into fibers. —

Type: Jongkind et al. 5811 (holo WAG 2 sheets [ WAG0159192 , WAG0159193 ]; iso BR, K, LBV [ LBV0004878 ], MO, UC, WAG-spirit [ WAG0115124 ]), Gabon, Nyanga, Doudou Mountains, Chantier SFN-Bakker, 310 m, 29 Nov. 2003 .

Etymology. Costus fenestralis has been named for its bracts which have a ‘gauze-like’ appearance caused by the withering of the mesophyll tissue between the veins creating a net-like structure like in rotting old leaves.The same happens in the sheaths on the shoot creating bunches of long fibers around the shoot below the insertion of the leaves.

Terrestrial herb 0.5–1 m tall. Leaves 1–4, crowded in a rosette at the top of the shoot; sheaths 0.5–1.5 cm diam, falling apart into separate fibers with age; ligule membranous, obliquely truncate to 1-lobed, 15–20 mm long; petiole absent or up to c. 3 mm long; sheaths, ligule and petiole densely covered with erect hairs <1 mm long to glabrous; lamina pale green on lower side, obovate, 22–35 by 10–15 cm, slightly c. 20-plicate, upper side rather densely covered with appressed to erect hairs 0.5–2 mm long, lower side densely so, base obtuse to cordate, apex acuminate (acumen 5–20 mm long). Inflorescence many-flowered, ovoid, 5–8 by 3.5–5 cm, terminating the leafy shoot; bracts and appendages on both sides densely covered with minute erect hairs <1 mm long, bracteoles with a row of hairs <1 mm long on the keel below the callus, calyx, ovary and capsule glabrous. Flowers 1 per bract; bracts green, chartaceous, depressed ovate, 1.4–1.5 by 2 cm, soon falling apart into separate fibers, callus sometimes present and then 1–2 mm long; appendages green, reflexed, broadly ovate, 0.7–1 by 2 cm; bracteole boat-shaped, 14–15 mm long, callus c. 2 mm long; calyx 13–15 mm long, split on one side, lobes triangular, 2–5 mm long, callus absent; corolla white, 40–60 mm long, glabrous, tube c. 10 mm long, lobes apically purplish, narrowly ovate, 30–50 mm long; labellum lilac, inner side with a yellow nectar guide, horizontally flattened, broadly obovate when spread out, 50–60 by 50–60 mm, margin crenate; stamen colour unknown, c. 30 by 10 mm, anther 6–7 mm long. Capsule and seeds not seen.

Distribution — Central Africa (Angola (Cabinda), Congo Brazzaville, Gabon).

Habitat & Ecology — In primary or secondary rainforest. At elevations of 300– 650 m. Flowering and fruiting: November and December.

Field observations — The flowers of C. fenestralis have been reported to be slightly fragrant (Jongkind et al. 5811).

IUCN Conservation Status — Based on an AOO of 44 km 2 from six locations of which only two are located in a protected area, while the others recently experienced logging or face several logging threats, we assess this species as Vulnerable (VU): B2ab(ii,iii,iv).

Other specimens examined. ANGOLA. Cabinda, Belize, 1 Jan.1919, Gossweiler 8232 ( BM). – CONGO BRAZZAVILLE, Lékoumou, Komono , 17 Jan. 1965, Bouquet 956 ( P); Vouala Mongomo, 5 Feb. 1965, Bouquet 1198 ( P); Route de M’bila, après le village Mouyabi, 12 Jan. 1968, Bouquet 2292 ( P). – GABON, Ngounié, route Malinga-Moukouagna, après village Nzinzi, 641 m, 12 June 2011, Bissiengou 1319 ( LBV, WAG). Nyanga, route Tchibanga-Mayumba, 19 Oct.2009, Bissiengou et al. 337 ( WAG); Doudou Mts, Chantier SNF-Bakker, 310 m, 29 Nov.2003, Jongkind et al.5811 ( LBV, WAG); Mouabissako, 8 Dec. 1907, Le Testu 1259 ( BM, P); Forêt du Mayombe, Ndabiliba (‘Dabiliba’), c. 300 m, 5 Feb. 1908, Le Testu 1299 ( BM, P); 50 km SSW of Doussala, 480 m, 14 Apr.1987, Reitsma et al.3230 ( MO, NY, WAG). Ogooué-Maritime, Doudou Mts, Reserve de Faune de Moukalaba , 350 m, 5 Dec. 1984, Arends et al. 651 ( BR, MO, P, WAG) .

Figures

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.