Costus lilaceus 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 : 303-304

14. Costus lilaceus Maas & H.Maas , sp. nov. — Plate 3d ; Map 9

Costus lilaceus can be recognized by its often epiphytic habit, pink to lilac flowers and its inflorescences placed laterally in the axil of a leaf or termi- nating a separate leafless shoot. —

Type: J.J.F.E. de Wilde et al. (WALK-B series) 40 (holo WAG 2 sheets [ WAG0114490 , WAG0114491 ]; iso BR, C, LBV, MO, P), Gabon, Woleu-Ntem, Crystal Mountains, 7 km along the road from Tchimbélé to Kinguélé, 620 m, 18 Jan. 1983 .

Epiphytic or sometimes terrestrial herb 0.3–1.6 m tall. Leaves many; sheaths 0.3–0.8 cm diam; ligule reddish brown to orange, membranous, truncate, 20–60(–80) mm long, often longer than the internode; petiole 2–15 mm long; sheaths, ligule and petiole glabrous; lamina shiny bright or pale green at upper side, less shiny, sometimes purplish or glaucous at lower side, (narrowly) elliptic or rarely (ob)ovate, more or less falciform, 9–30 by 3–8 cm, coriaceous and somewhat fleshy, glabrous on both sides, base acute to obtuse, apex acute to acuminate (acumen 15–20 mm long). Inflorescences generally several per flowering branch, each one few- to several-flowered, ovoid to ellipsoid, (1–)1.5–5 by 1–2.5 cm, lateral in the axil of a leaf with a peduncle 0.5–2.5 cm long or terminating a separate leafless shoot emerging from the rhizome 0.8–1 cm long or terminating a leafy shoot; bracts, bracteoles, calyx, ovary and capsule sparsely to rather densely covered with erect hairs <1 mm long. Flowers 1 per bract; bracts dark reddish brown to dark green with red dots, old bracts (pale) brown, chartaceous, narrowly to broadly elliptic-(ob)ovate, 0.3–1.1 by 0.1–1.1 cm, callus yellowish green, 0.5–1.5 mm long, sometimes inconspicuous; appendages absent; bracteole tubular, 7–9 mm long, callus green, 1–1.5 mm long; calyx pale green to crimson to dark reddish brown, 7–23 mm long, lobes shallowly triangular 1–2.5 mm long, callus yellowish green, 1–2 mm long; corolla hyaline, white, 30–50 mm long, glabrous, tube 10–15 mm long, lobes narrowly elliptic, 30–40 mm long; labellum at the outer side basally white, upper part pale lilac, inner side pale pink to lilac or rarely white (see note), with bright yellow to orange nectar guide and reddish dots and hairs at the base, horizontally flat- tened with funnel-shaped base, broadly obovate when spread out, 35–70 by 30–65 mm, margin irregularly crenate undulate; stamen white to pale pink with reddish dots, 30–35 by 10–12 mm, apex bright yellow, anther 9–10 mm long. Capsule ellipsoid to broadly ellipsoid, 6–7 by 4 mm. Seeds c. 1 mm diam.

Distribution — West Africa (Nigeria); Central Africa (Cam- eroon, Congo Brazzaville, Congo Kinshasa, Equatorial Guinea, Gabon).

Habitat & Ecology — In primary or sometimes secondary rainforest, in wet places (epiphytic specimens), but also in savanna forest in rocky places or on outcrops (terrestrial speci- mens), at elevations of 80–1530 m. Flowering and fruiting: all year through, especially in January.

IUCN Conservation Status — This species with about 22 locations and an AOO of 248 km 2 is assessed as Least Concern (LC).

Representative specimens examined. CAMEROON, Littoral Province, Forêt de Bakaka, 3 km E of Eboné (on km 11 of Nkongsamba-Loum Road), 520 m, 28 Jan. 1972, Leeuwenberg 9317 ( BR, K, MO, P, WAG, YA) . South Province, Lolodorf, 8 Jan. 1968, Bamps 1748 ( BR) . South-West Province, Mts Rumpi, near Dikome Balue, 35 km NNW of Kumba, 1200 m, 25 Mar. 1976, Letouzey 14578 ( P), Bakossi Mts, W of Bangem, 1400 m, 3 Jan.1986, D.W. Thomas 5262 ( MO, NY) . – CONGO BRAZZAVILLE, Kouilou, cultivated at Pointe Noire, originating from Maiombe, région de Dimonika, 29 Oct. 1988, De Foresta 1739 ( P) . Niari, border of Congo Brazzaville and Gabon, 500 m from the Loambitsi River, 4 Feb. 1975, Sita 3884 ( BR) . – CONGO KINSHASHA, Nord-Kivu, Kitshanga, 1300 m, 7 Jan. 1959, A. Léonard 2348 ( BR) . Sud- Kivu, Territoire Kalehe,km 110 of road from Kavumu to Walikale,Irangi,near River Luhoho, 850 m, 6 Dec. 1956, Christiaensen 1920 ( BR, U) . – EQUATORIAL GUINEA, Centro Sur, Bata-Monte Alén, 18 Mar. 1994, Carvalho 5488 ( WAG) ; Parque Nacional de Monte Alén, near Lago Atok, 2 July 1998, Pérez Viso 19 ( WAG) . – GABON, Estuaire, Monts de Cristal, Mkam-Mela, 950 m, 30 Jan. 1968, Hallé & Villiers 4746 ( P) . Ngounié, 25 km NE of Mouila, 19 Dec.1985, Wilks 1166 ( WAG) . Nyanga, 25 km SW of Doussala, 11 Jan. 1987, Reitsma & Reitsma 2835 ( MO, NY, WAG) . Ogooué-Ivindo, road on Babiel-Nord, few kms W of Belinga, 900 m, 18 July 1985, Bos et al. 10685 ( BR, MO, WAG) . – NIGERIA, Ogoja, Ikwette-Balegeta path, 4500 ft, 29 Dec. 1948, Savory & Keay FHI 25202 ( K, P) .

Notes — Costus lilaceus can only be separated from C. lateriflorus by the colour of the labellum of the flowers being yellow in C. lateriflorus but pink to lilac in C. lilaceus . Many specimens have wrongly been identified as C. letestui , assuming the flowers of this species were lilac in colour (Koechlin 1964, 1965). As C. letestui turned out to be a synonym of C. lateriflorus (see under that species), these specimens with pink to lilac flowers needed a new name: C. lilaceus . Costus lilaceus has been found epiphytic in trees up to 25 m high on Parkia bicolor (Bamps 1612) , Gilbertiodendron dewevrei (Christiaensen 1826 and 1920) and Julbernardia (Letouzey 12730). The plant forms a clump with pendant shoots. When terrestrial it is often found at high altitude growing over rock, forming a ‘dense mat of Costus between the trees and shrubs’ (A.M. Louis 2318). Studying the distribution of C. lilaceus and C. lateriflorus we found a difference in the altitude where both species occur: C. lilaceus is generally found growing at higher elevations (80–1530 m), avoiding the sedimentary basin; C. lateriflorus seems to prefer the coastal sedimentary areas of Gabon and Cameroon (0–800 m). Some specimens of C. lilaceus have flowers with a very pale lilac to almost white labellum and a bright yellow nectar guide.

Figures

Plate 3 a. Costus kupensis Maas & H.Maas. Basal inflorescence. – b. Costus lateriflorus Baker. Habit showing lateral inflorescences. – c. Costus tappenbeckianus J.Braun & K.Schum. Inflorescence with flower. – d. Costus lilaceus Maas & H.Maas. Lateral inflorescence. – e. Costus phyllocephalus K.Schum. Inflorescence. – f. Costus maboumiensis Pellegr. Inflorescence (a: Maas et al. 10575; b: photographed in Lyon Arboretum Hawaï, no specimen collected; c: Burgers’ Bush number 20140016; d: photographed in Burgers’ Bush, Arnhem, The Netherlands, no specimen collected; e: Maas et al. 10407; f: Maas et al. 10227). — Photos: a, c–f: P.J.M.Maas; b: J.Mood.

Map 9 Distribution of Costus lilaceus Maas & H.Maas (●) and C. talbotii Ridl. (▲).