Costus louisii H.Maas & 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 : 305

16. Costus louisii H.Maas & Maas , sp. nov. — Plate 4f ; Map 10

Costus louisii looks superficially like C. afer but can be distinguished by having shiny leaves, 1 flower per bract, shiny green bracts and completely pinkish red flowers. —

Type: Maas et al. 10339 (holo WAG; iso K, L-spirit [ L0298233 ], LBV, MO, UC), Gabon, Estuaire, Libreville , Glass , garden of A.M. Louis, at sea level, 6 Nov. 2011, cultivated from a specimen collected by A.M. Louis, 30 km S of Mayumba, within walking distance of the ocean, on white sand, in swampy low forest .

Terrestrial herb 1.5–2.5 m tall. Leaves many; sheaths 0.8–1.1 cm diam; ligule chartaceous, unequally 2-lobed, 10–29 mm long, apical margin with white curly fibers; petiole 5–10 mm long; sheaths, ligule and petiole glabrous except for some long hairs at the very base of the leaves, many on the upper margin of the ligule and also some on the border between the petiole and the sheath; lamina upper side dark green, lower side pale green, shiny at both sides or only at the upper side, narrowly ovate-elliptic (to obovate), 20–29 by 6–10 cm, both sides and margin glabrous except for some erect hairs <1 mm long, base acute (to slightly cordate), apex acuminate (acumen 15–35 mm long). Inflorescence many-flowered, ovoid, (4–)7–10 by 4–6 cm, terminating the leafy shoot; bracts, appendages of bracts, bracteoles, calyx and ovary glabrous. Flowers 1(–2) per bract; bracts basally green with shiny brown to dark red upper part, coriaceous, broadly ovate-triangular to ovate-triangular, 2–3 by 2–3 cm, callus absent; appendages generally absent; bracteole boat-shaped, 20–21 mm long, callus (pale) green c. 2 mm long; calyx 17–21 mm long, lobes triangular, 3–4 mm long, callus absent; corolla white, 50–60 mm long, glabrous, tube 10–15 mm long, lobes white with pink apex and yellow base, narrowly elliptic, 40–45 mm long; labellum at the outer side white, inner side basally white, upper part completely (striped with) dark pink, throat and nectar guide yellow, horizontally flattened, broadly obovate to circular when spread out, 45–50 by 50–55 mm, margin crenate and undulate; stamen white with dark pink apex, 30–35 by 10–15 mm, apex (dark) pink, anther 7–8 mm long. Capsule and seeds not seen.

Distribution — Central Africa (Gabon).

Habitat & Ecology — In swampy low forest or savanna, on white sand, at elevations of about sea level. Flowering and fruiting: November.

Field observations — The plants are pollinated by small birds; capsule and seeds were never seen (A.M. Louis, pers. comm.).

IUCN Conservation Status — This species is only known from a single wild collection (AOO = 4 km 2) from a small popula- tion, and one plant in cultivation. This location does not have any protected status.Although it is not immediately threatened, there is some tourism development in the area. We assess this species as Critically Endangered (CR) B2ab(iii,v); D .

Notes — Costus louisii looks very much like C. afer , both having many-flowered inflorescences that terminate the leafy shoots. In C. louisii , however, the leaves are shiny at both sides, whereas the leaves of C. afer are never shiny. Moreover, the labellum of the flowers of C. louisii is horizontally flattened and completely dark pink with yellow nectar guide, while that of C. afer is funnel-shaped and white with a yellow nectar guide and red colouring restricted to the margins. The material of C. louisii has all been collected from plants now in cultivation in the greenhouses of Burgers’ Bush,Arnhem, The Netherlands and of Royal Botanic Gardens, Kew, London, Great Britain. They originate from the type specimen growing in the garden of A.M. Louis, who collected it 30 km S of Mayumba, Gabon, within walking distance of the ocean, on white sand, in swampy low forest (S3°36’ E10°52’) .

Figures

Plate 4 a. Costus macranthus K.Schum. Habit, flower and details of stamen, stigma and style. – b. Costus nimba H.Maas & Maas. Basal inflorescence. – c. Costus spectabilis (Fenzl) K.Schum.Habit with flowers. – d. Costus lucanusianus J.Braun & K.Schum. Inflorescence with 4 flowers.– e. Costus talbottii Ridl. Flower. – f. Costus louisii H.Maas & Maas. Inflorescence (a: Wright 1905: t 7992; b: Jongkind 11301; c: photographed in Rumonge, SW Burundi, no specimen collected; d: Maas et al. 10000; e: Maas et al. 9800; f: Maas et al. 10339). — Photos: a, b, d–f: P.J.M.Maas; c: E. Fischer.

Map 10 Distribution of Costus louisii H.Maar & Maas (▲) and C. tappen- beckianus (●).