Coleus esculentus var. primulinus (Baker) Meerts & Paton, 2024

Meerts, Pierre J. & Paton, Alan J., 2024, The genus Coleus (Lamiaceae) in Central Africa (Democratic Republic of the Congo, Rwanda, Burundi), with the description of 15 new species, PhytoKeys 246, pp. 71-178 : 71-178

Coleus esculentus var. primulinus (Baker) , comb. et stat. nov.

Plectranthus primulinu s Baker in Bull. Misc. Inform., Kew 107: 292. 1895. Type: Zambia, Mwero Plateau, 1894, A. Carson 36 (holotype K [ K 000430746]). (Basionym)

Description.

Closely related to var. densus , differing in the much shorter thyrses, with rachis obsolete, mostly grouped into a spiciform inflorescence in the upper part of the stem; calyx lobes 2–3 mm long, equalling the tube.

Distribution.

Angola, Zambia, DR. Congo, W Tanzania.

Habitat and ecology.

Savannah, wooded savannah, in DR. Congo often on Cu / Co or Mn rich soil, 1170–1830 m elev.

Additional specimens.

DR. Congo, Haut-Katanga, Upemba, Piste vers Mitwaba, 12 Apr 1947, G. F. de Witte 2488 ( BR); Kasompi Est, Jul 1956, P. Duvigneaud & J. Timperman 2051 ( BRLU); Kabwelunono copper hill, Jun 1997, F. Malaisse, E. Kisimba, Y. Muzinga 134 ( BR); Kwatebala copper hill, May 2007, I. Parmentier 4347 ( BR; WAG); Upemba, tête de source de la Katuba, Aug 1934, P. Quarré 4213 ( BR); Kipopo, 20 May 1982, M. Schaijes 1397 ( BR); Chabara, 11 Apr 1990, Tropmetex 224 ( BR, MO).

Notes.

1. Previous treatments ( Paton et al. 2009, 2013) synonymised Plectranthus primulinus with Coleus densus . However, in DR. Congo, the two morphs can be readily recognised even though intermediates occur; therefore, we propose to recognise them at varietal rank. They occur in different habitats, var. primulinus being particularly frequent in steppic savannah on metal-rich soil in Haut-Katanga, where var. densus is rarely observed.

2. Specimens collected in the rainy season consist of leafy shoots without flowers, with leaves steadily decreasing in size upwards, the upper ones bract-like and often forming an apical coma; specimens collected in the dry season are mostly leafless and bear inflorescences in the upper part of the stem. Some specimens have particularly large leaves (up to 20 × 8 cm) with velvety tomentose indumentum (e. g. G. F. de Witte 2488).