Paracostus englerianus (K.Schum.) C.D.Specht

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 : 312-313

1. Paracostus englerianus (K.Schum.) C.D.Specht — Plate 1e ; Map 15

Paracostus englerianus (K.Schum.) C.D.Specht in Specht & Stevenson (2006) 162. — Costus englerianus K.Schum. (1892) 419, t. 13 (2 Aug. 1892); (1904) 424. — Type: Preuss 461 (holo B destroyed), Cameroon, W of Barombi-ba-Mbu, 2 Sept. 1890. As the holotype in B has been de- stroyed,the illustration accompanying the protologue (K.Schumann 1892: Tafel 13), which is the only remaining original material, is here designated as the lectotype .

Costus unifolius N.E.Br. (1892) 696 (10 Dec. 1892), syn.nov. — Type: Cultivated in Kew Gardens in 1892 from material received from Sander & Co., who collected it in 1891 in Ghana (‘ Gold Coast’ ) (holo K) .

Terrestrial, prostrate herb 0.2–0.3 m tall; rhizomes> 20 cm long, repeatedly branched, horizontally creeping, 1.5–7 mm diam, shoots reddish, provided with brown membranous sheaths 1.2–1.9 by 0.5–0.8 cm and roots with side roots to c. 10 cm long. Leaves 1 per shoot; description of sheaths see under inflorescence; ligule and petiole absent; lamina green to shiny dark green above, paler green to whitish green below, elliptic to obovate or broadly so, 8–19 by 5–13 cm, 3–4-plicate, glabrous on both sides, base attenuate, extreme base of leaf fleshy, 10–20 mm long, at an angle of 45° with the lamina, sur- rounding the inflorescence, apex obtuse, minutely apiculate. Inflorescence axillary, 1–7-flowered, 0.5–1.3 cm long, the lower portion enclosed by the more or less overlapping margins of the base of the lamina and by the uppermost 1–3 sheathing leaf bases; sheaths to c. 6 by 1.3 cm, apex acute to obtuse; bracts, bracteoles and calyx rather densely covered with soft, erect hairs c. 1 mm long, ovary glabrous; bracts reddish brown, green, or yellow, membranous, broadly to depressed ovate, 0.7–1.5 by 1–1.3 cm, callus absent; appendages absent; bracteole pale brown to green, boat-shaped, 12–13 mm long, callus absent; calyx pale brown to green, 9–20 mm long, lobes (broadly) triangular, 1–4 mm long, callus absent; corolla white to pale green, 28–35 mm long, glabrous, tube 10–15 mm long, lobes erect, narrowly ovate-triangular, 18–20 mm long; labellum white to slightly pink, inner side with yellow or orange nectar guide in the throat, horizontally flattened, (broadly) obo- vate when spread out, 20–50 by 12–30 mm, margin crenate; stamen white, 15–35 by (1.5–) 3–4 mm, apex yellow, anther 2–3 mm long; stigma is composed of a funnel-shaped upper part and a reflexed lamellate part; appendage absent. Fruit and seeds not seen.

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Distribution — West Africa (Benin, Ghana, Ivory Coast, Ni- geria); Central Africa (Cameroon, Congo Brazzaville, Equatorial Guinea, Gabon).

Habitat & Ecology — Understory of lowland rainforest, often forming dense patches and growing on rocks. At elevations of 0–1100 m. Flowering and fruiting: all year through.

IUCN Conservation Status — Paracostus englerianus with around 50 locations of which 14 have a protected status and an AOO of 484 km 2 is assessed by us as Least Concern (LC). However, we need to note that nearly the entire distribution in Upper Guinea (West of the Dahomey Gap) is present in unprotected areas (only the locality in the Atewa Range has some protection, but see Hoekstra et al. 2016), while this area is seriously facing habitat destruction. If this somewhat isolated part of the species would prove to possess unique genetic (or morphological) features, these populations should get some attention and might need to be assessed separately.

Note — Paracostus englerianus is distinguished from other African Costaceae by its prostrate and often lithophilic habit, 1 solitary leaf per shoot, few-flowered inflorescence with inconspicuous bracts and relatively small whitish flowers. The inflorescence of P. englerianus is axillary. According to Specht & Stevenson (2006) the inflorescence emerges from the axil of the leaf and appears terminal due to secondary displacement along with lack of continued growth of the shoot apical meristem.

Figures

Plate 1 a. Costus afer Ker Gawler. Flower. – b. Costus aureus Maas & H.Maas. Inflorescence.– c. Costus albiflos Maas & H.Maas. Inflorescence.– d. Costus dinklagei K.Schum. Habit and details. – e. Paracostus englerianus (K.Schum) C.D.Specht. Habit with flower. – f. Costus ligularis Baker. Inflorescence (a: Maas et al. 10023; b: photographed in Ghana,no specimen collected; c: Maas et al. 10411; d: N. Hallé 4129, drawing in his collecting book; e: photographed in Botanical gardens Utrecht, no specimen collected; f: Maas et al. 9794). — Photos: a, c, f: P.J.M.Maas; b: T.R.van Andel; d: C.D.Specht; e: L.Y.T.Westra.

Map 15 Distribution of Paracostus englerianus (K.Schum.) C.D.Specht.