Costus obscurus D.Skinner & Maas, 2023

Maas, Paul J. M., Maas-van de Kamer, Hiltje, Andre, Thiago, Skinner, David, Valderrama, Eugenio & Specht, Chelsea D., 2023, Eighteen new species of Neotropical Costaceae (Zingiberales), PhytoKeys 222, pp. 75-127 : 75

Costus obscurus D.Skinner & Maas sp. nov.

Diagnosis.

Costus obscurus sp. nov. (Fig. 14 ) can be recognized by its large, dark green leaves with dark purple undersides and densely whitish villose sheaths. It could superficially be confused with C. erythrophyllus Loes. and C. acreanus (Loes.) Maas, but these species never have densely villose sheaths.

Type.

Peru, Madre de Dios: Prov. Manu, near Shintuya, on road to Salvación, 600 m, 9 Feb 1974, Plowman & Davis 5054 (holotype USM; isotypes GH, L1483069, L1480371, L1480372) .

Description.

Herb 1-1.5 m tall. Leaves sheaths 10-20 mm diam; ligule truncate, 10-15 mm long; petiole 8-12 mm long; sheaths, ligule and petiole densely to rather densely whitish villose; lamina narrowly elliptic, 32-45 × 9-17 cm, adaxially dark green, rather densely to densely whitish villose, abaxially dark purple, densely to sparsely whitish puberulous, base acute to cordate, apex acuminate (acumen 5-10 mm long). Inflorescence ovoid, 8-13 × 5-7 cm, terminating a leafy shoot; bracts, appendages of bracts, bracteole, calyx, ovary, and capsule rather densely to sparsely puberulous. Flowers abaxially oriented; bracts green in the exposed part, red or green in the covered part, coriaceous, broadly ovate-triangular, 35-45 × 30-35 mm; appendages green, erect, broadly ovate-triangular, 15-20 × 18-20 mm, or almost absent, apex rounded; bracteole boat-shaped, 35-37 mm long; calyx red, 25-27 mm long, deeply split on one side, lobes deltate to broadly triangular, ca. 2 mm long; corolla cream to yellow, ca. 75 mm long, glabrous, lobes narrowly elliptic, 55-60 mm long; labellum pale yellow, distal edge horizontally spreading, broadly obovate, ca. 60-70 × 60-70 mm, lateral lobes strongly striped with pink or red, middle lobe reflexed, with yellow honey mark, margin irregularly dentate to lobulate; stamen white to pink, 35-45 × 12-15 mm, not exceeding the labellum, apex pinkish red, deeply and irregularly lobed, anther 7-8 mm long. Capsule ellipsoid, 12-15 mm long.

Distribution.

Peru (Cuzco, Huánuco, Madre de Dios, San Martín) (Fig. 22C ).

Habitat and ecology.

In forests, in wet, shady areas, often in disturbed places, at elevations of 450-1300 m. Flowering in the rainy season.

Etymology.

Costus obscurus sp. nov. is known for its leaves having a very dark green adaxial surface and dark purple abaxial surface, and for growing in dark and shady places, hence the specific epithet obscurus ( ‘obscurus’ means 'dark, shady, “indistinct’ in Latin). This species might also be considered “obscure” (in English: unclear, uncertain, unknown, or in doubt) because it has been confused by the authors in the past as either C. erythrophyllus Loes. or as C. acreanus (Loes.) Maas. Only recently has it been determined to be an undescribed species.

Paratypes.

Peru. Cuzco: Prov. La Convención, Distr. Echarati, Cashiriari-3 well site, 5 km S of Camisea River, 700 m, 2 Sep 1998, Nuñez V. et al. 23785 (F). Huánuco: Prov. Leoncio Prado, Puente Pucayaco, Río Pucayaco, road from Tingo Maria to Tocache, 570 m, 30 Mar 1976, Plowman & Kennedy 5775 (U); cultivated in Tocache, besides Maior Plaza, originally collected by José Schunke V. at Quebrada Cachiyaco de Lopuna, near Mina de Sal, S of Tocache, 31 Mar 1976, Plowman & Kennedy 5791 (GH, U); cultivated in Jardin Botanico de Tingo Maria, from material collected by Plowman in Ramal de Aspusana, 65 km N of Tingo Maria, on the border of Huánuco and San Martín, 5 Jul 1978, Plowman & Ramírez R. 7595 (F, U). Madre de Dios: Prov. Manu, Cerro de Pantiacolla, Río Palotoa, 10-15 km NNW of Shintuya, 700-1300 m, 16 Dec 1985, Foster et al. 10937 (F); Pantiacolla, serrania across Río Alto Madre de Dios from Shintuya, 450-650 m, 28 Oct 1979, Gentry 27304 (MO, U). Cultivated material: Harvard Forest Greenhouses, Petersham, Massachusetts, USA, cultivated from Plowman & Davis 5054, Peru, Plowman & Davis 5054 A (F, L); cultivated from Peru, Huánuco, 8 km NW of Tingo Maria, along quebrada on road to Shinchi Roca, 900 m, 14 Nov 2016, Skinner R3383 (BH). Peru, Madre de Dios, Pantiacolla, 25 Jan 2013, Skinner R3322 (UC).

Notes.

Plants of Costus obscurus sp. nov. have a compact appearance, with leaves closely spaced together along the shoot and generally pointed upward rather than horizontally or drooping. The leaves’ dark green adaxial surface and dark purple abaxial surface are striking in appearance. Costus obscurus can be confused with C. erythrophyllus Loes., but can be distinguished from that species by its shorter, truncate ligule instead of a long and deeply 2-lobed ligule as well as by having smooth rather than (mostly) plicate leaves.

This new species has been widely cultivated from the type collection Plowman 5054. Plowman’s journal indicates the distribution of live plants to Marie Selby Botanical Garden and Lyon Arboretum, which is accessioned as L-81.0901. It has sometimes been confused with the famous "El Whiskey" plant from Colombia, but it can be easily distinguished by the indumenta on the adaxial and abaxial leaf surfaces.

Figures

Figure 14. Costus obscurus D. Skinner & Maas A cultivated plant from Plowman's type collection showing upright orientation of leaf lamina B inflorescence C cultivated plant showing colours and upright orientation of leaf lamina D photo showing villose indument on leaf sheaths E Indument on adaxial leaf surface F indument on abaxial leaf surface A, B cultivated specimen from Lyon Arboretum, Hawaii L- 81.0901 grown from seeds wild collected by Tim Plowman from the plant accessioned as Plowman 5054 C-F photos taken in Pantiacolla, Madre de Dios, Peru prior to collecting seeds for D. Skinner R 3322, currently in cultivation. Photos A-F by Dave Skinner.

Figure 22. Distribution maps for new species of Costaceae. Costus gibbosus - Costus whiskeycola m A Costus gibbosus D. Skinner & Maas B Costus mollissimus Maas & H. Maas C Costus obscurus D. Skinner & Maas D Costus oreophilus Maas & D. Skinner E Costus pitalito C. D. Specht & H. Maas F Costus prancei Maas & H. Maas G Costus pseudospiralis Maas & H. Maas H Costus rubineus D. Skinner & Maas I Costus whiskeycola Maas & H. Maas.