12. Costus lateriflorus Baker — Plate 3b; Map 8

Costus lateriflorus Baker (1898) 301; K.Schum. (1904) 413. — Type: Mann 1629 (holo K; iso P), Equatorial Guinea, Litoral Prov., Corisco Bay, Mount John, River Kongui, Aug. 1862.

Costus letestui Pellegr. (1929) 220 (as ‘ Le Testui ’), syn. nov. — Type: Le Testu 1683 (holo P; iso BM, K), Gabon, Nyanga, Tchibanga area, Mayombe bayaka, Ighouma, 8 km NE from Mouila, 12 Jan. 1913.

Epiphytic or sometimes terrestrial herb to c. 1.5 m tall. Leaves many; sheaths 0.4–0.7 cm diam; ligule reddish brown, mem- branous, truncate, 25–40 mm long, sometimes longer than the internode; petiole 4–10 mm long; sheaths, ligule and petiole glabrous; lamina sometimes purplish on lower side, coriaceous and somewhat fleshy, narrowly elliptic, 9–20 by 2–6.5 cm, glabrous on both sides, base acute to obtuse, apex acuminate (acumen 5–12 mm long). Inflorescences generally several per flowering branch, each one few- to several-flowered, ovoid, 2–4 by 1–3 cm, lateral in the axil of a leaf with a peduncle 1–4 cm long or terminating a separate leafless shoot c. 1 cm long or terminal on a leafy shoot; bracts, bracteoles, calyx, ovary and capsule rather densely to densely covered with erect hairs <1 mm long, rarely glabrous. Flowers 1 per bract; bracts pale brownish green to reddish brown, slightly dotted with pink, chartaceous, ovate, 0.5–1 by 0.3–0.8 cm, callus sometimes present and then c. 1 mm long; appendages absent; bracteole tubular, 8–12 mm long, callus sometimes present and then c. 1 mm long; calyx pale pinkish green to reddish brown with pale green lobes, 12–18 mm long, lobes shallowly ovatetriangular, 1–2 mm long, callus distinct, green, 1–2 mm long; corolla hyaline, whitish with some pink or brown and red dots, 35–50 mm long, glabrous, tube 15–20 mm long, lobes narrowly elliptic-ovate, 20–35 mm long; labellum at the inner and outer side bright yellow, horizontally flattened with funnel-shaped base, broadly obovate when spread out, 40–60 by 35–60 mm, margin crenulate; stamen white with red dots, 20–27 by 8–11 mm, apex yellow, anther 7–10 mm long. Capsule ellipsoid, c. 12 by 6 mm. Seeds c. 1.5 by 1 mm.

Distribution — West Africa (Nigeria); Central Africa (Cam- eroon, Central African Republic, Equatorial Guinea, Gabon).

Habitat & Ecology — In primary or sometimes secondary rainforest rich in Caesalpinioideae and Sacoglottis gabonensis, sometimes epiphytic on Baillonella toxisperma and Tetraberlinia bifoliolata, or on sandy to rocky soil, at elevations of 0– 800 m. Flowering and fruiting: all year through.

IUCN Conservation Status — Costus lateriflorus occurs in about 17 locations with an AOO of 104 km 2. Six of these loca- tions have a protected status. Since we are unable to identify material of this species or C. lilaceus where the petal colour is not apparent, this species is likely to be more common than currently assessed. We therefore assess it as Least Concern (LC).

Notes — Costus lateriflorus can be recognized by its mostly epiphytic habit, flowers with a bright yellow labellum and its inflorescences placed laterally in the axil of a leaf or terminating a separate leafless shoot. However, it is almost impossible to distinguish C. lateriflorus from C. lilaceus except for the strik- ing difference they show in the colour of their labellum: yellow in C. lateriflorus and lilac in C. lilaceus. In the material studied we found 12 specimens to be unidentifiable due to lack of information regarding flower colour on the label. The shoot of C. lateriflorus is brown (ligule) alternating with green (internodal part of the stem). The labellum of the flowers of C. letestui Pellegr., now in syn- onymy with C. lateriflorus, was described by Koechlin (1965, 1965) as being pink. However, the flowers of C. letestui are yellow, as in C. lateriflorus Baker, because the label of the type specimen Le Testu 1683 (P) reads: ‘Epiphyte à fleurs jaunes’.