Costus ligularis Baker

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 : 303

13. Costus ligularis Baker — Fig. 1f ; Map 4

Costus ligularis Baker (1898) 298; K.Schum. (1904) 390. — Type: Mann 1628 (holo K 2 sheets), Equatorial Guinea, Litoral Prov., Corisco Bay, Muni River (‘ Danger River’), Aug. 1862 .

Costus araneosus Gagnep. (1902a) 95, syn. nov. — Type: De Brazza 100 (holo P), Congo Brazzaville, Brazzaville , Sept.-Oct. 1884 .

Costus fimbriatus Pellegr. (1929) 220, syn. nov. — Type: Le Testu 1817 (holo P; iso BM, BR, P), Gabon, Nyanga, Tchibanga area, Maboumi Camp , Mayombe bavili , 27 Oct. 1914 .

Costus ngouniensis Pellegr. (1938) 41, nom.nud., without Latin description. — Based on: Le Testu 2238 ( BM, BR, P), Gabon, Ngounié, Nzouna , 22 Oct. 1917 .

Terrestrial herb 0.3–0.5(–1.5) m tall. Leaves 2–6(–8), often condensed at the top of the shoot in an apical rosette; sheaths dark red, 0.2–1.5 cm diam, sometimes creamy, falling apart into separate fibers with age; ligule dark reddish brown, mem- branous, truncate or 2-lobed, 5–50 mm long; petiole 3–15 mm long; sheaths, ligule and petiole densely to sparsely covered with erect hairs to c. 3 mm long; lamina sometimes red to purple on lower side, narrowly obovate to elliptic, 9–23 by 4–10.5 cm, 3–5-plicate (Maas et al. 10212), chartaceous, upper and lower side densely to sparsely covered with soft erect hairs to c. 3 mm long, base acute, apex acute to acuminate (acumen 10(–15) mm long). Inflorescence few- to several-flowered, broadly ovoid to globose, 1–4 by 1–4 cm, terminating the leafy shoot or rarely terminating a separate leafless shoot 2–7(–20) cm long; bracts, appendages of bracts, bracteoles, calyx and ovary sparsely to rather densely covered with appressed hairs <1 mm long. Flowers 1 per bract; bracts apically dark brown-red with darker dots, chartaceous, ovate to broadly ovate, 0.8–1.8 by 0.5–2.4 cm, callus absent or present and 1–2 mm long; appendages generally present, brownish red, ascending, horizontally spreading or reflexed, broadly ovate, 0.2–0.7(–2) by 0.2–0.5(–2) cm, bracteole boat-shaped, 7–15 mm long, callus distinct, yellowish to whitish, 1.5–2 mm long; calyx whitish with pink upper part, 5–12 mm long, lobes shallowly triangular, 1–2 mm long, callus absent; corolla hyaline, pink to red to brown, 55–65 mm long, glabrous, tube 10–15 mm long, lobes narrowly elliptic, 45–55 mm long; labellum white to pink on the outer side, inner side white with broad pink to purple margin, base of throat often yellow, no nectar guide present, horizontally flattened, broadly obovate when spread out, 50–80 by 40–70 mm, margin fimbriate, more or less 5-lobed, and crenate; sta- men white, 30–40 by 10–20 mm, apex yellow to orange, very tip pink, anther 5–8 mm long. Capsule and seeds not seen.

Distribution — Central Africa (Cameroon, Congo Brazzaville, Equatorial Guinea, Gabon).

Habitat & Ecology — In rainforest, sometimes growing along river banks, in lateritic to sandy soils, at elevations of 0– 800 m. Flowering and fruiting: all year through, especially in January.

IUCN Conservation Status — Least Concern.

Notes — Costus ligularis is a species of small stature that can be distinguished by its dark red sheaths, softly hairy leaves (on both sides), small and dark reddish brown appendaged bracts, very distinct calli on the bracteoles, a pinkish labellum without nectar guide and a relatively small inflorescence (1–4 by 1–4 cm). The absence of a nectar guide inside the throat of the C. ligularis flower is functionally ‘replaced’ by the yellow apex of the stamen, which is turned upwards and highly visible. Costus ligulari s differs from the similarly looking C. phyllocephalus by having a small inflorescence of 1–4 by 1–4 cm, com-posed of relatively small dark reddish brown bracts, bracteoles and calyx. The bracts are 0.8–1.8 cm long, the appendages 0.2–0.7 cm long. The bracteoles are 7–15 mm long with a callus of 1.5–2 mm long. This yellowish callus is prominently visible contrasting with the dark reddish brown bracteole. In contrast C. phyllocephalus has an inflorescence of 2.5–10 by 3–7 cm, composed of relative large, green to reddish purple bracts, bracteoles and calyx. The bracts are 1–2.5 cm long, the appendages 1–4.5 cm long. The bracteoles are 11–21 mm long with a callus 2–3.5 mm long; this callus is not very distinct.

Figures

Map 4 Distribution of Costus dinklagei K. Schum. (●) and C. ligularis Baker (■).

Fig. 1 Schematic details (* = node of shoot). a. Ligule shapes (the utmost right one: C. lucanusianus); b. ligule lengths (left: C. lateriflorus); c. 1-flowered bract with 1 bracteole and 1 flower; d. 2-flowered bract with 2 bracteoles and 2 flowers; e. drawing of bract with nectary, 2 appendaged bracts, bracteole with nectary, and ovary and calyx with nectary on apex of lobes. — Drawing by Hendrik Rypkema.