Streptocarpus malachiticola Eb.Fisch. & I.Darbysh., 2021

Fischer, Eberhard & Darbyshire, Iain, 2021, Five new species of Streptocarpus (Gesneriaceae) from Katanga, D. R. Congo, Plant Ecology and Evolution 154 (2), pp. 264-280 : 265-268

Streptocarpus malachiticola Eb.Fisch. & I.Darbysh. , sp. nov.

( figs 1–2 , 9A ) –

Type: D.R. CONGO – Haut Katanga • Le long du ruisseau Tshilongo , à proximité du village Kabwe , rochers bordant la rive droite, paroi verticale; 1370 m; 10°37′S, 26°05′E; 10 Jan. 1980; Malaisse 11427; holotype: BR[BR0000016803312] .

Diagnosis – Streptocarpus malachiticola differs from S. goetzei in the glandular-pubescent pedicel with shorter eglandular hairs intermixed, the glandular-pubescent calyx, the smaller corolla with glandular hairs outside, the glandular-pubescent ovary, the bilobed stigma and the distinctly shorter capsule. The upper lip of the corolla bears strongly divaricate lobes, thus also differing from S. goetzei . It differs from S. compressus in the strictly unifoliate habit, the glandular-pubescent calyx, the shorter lower lip of the corolla, the blue-violet corolla with pale-whitish palate, the shape of the upper lobes and the more strongly constricted mouth, the eglandular style and the shorter capsules.

Description – Perennial acaulescent herb. Unifoliate, the phyllomorph on a short petiolode, 1 × 0.5 cm, lamina green, broadly oblong, ca 5–18 × 2–7 cm, with dense whitish hairs, base cordate, margin crenate, with 7–12 pairs of lateral nerves. Inflorescences 1–2 per plant at base of lamina, 6.5–19 cm long. Pedicel 10–18(–25) mm long, glandularpubescent with intermixed much shorter eglandular hairs, bracts linear-lanceolate, 1–2 × 0.5–0.8 mm. Calyx 4–6 mm long, divided to the base, hairs on calyx glandular-pubescent. Corolla purple-blue with whitish mouth, 17–24 mm long, mouth distinctly compressed between the two upper lobes with the opening shaped like an inverted V, hairs on corolla glandular-pubescent, tube 9–13 mm long, tube diameter 2–3 mm, widening at mouth to 4 mm, upper lip 4–6 mm long, lobes 3.5 × 4.5 mm, lower lip 7–10 mm long, lateral lobes 5.5 × 4.5 mm, median lobe 6 × 5 mm. Stamens inserted at 2/3 rd of corolla tube, filaments 2 mm long, with few short glandular hairs, anthers rounded, thecae 1.5 mm long, staminodes minute, ca 0.5 mm long. Ovary and style 4–7 mm long, ovary densely glandular-pubescent, style with short eglandular hairs, stigma bilobed, 0.8–0.9 × 0.5 mm. Capsules slender, 20–22 × 2 mm.

Distribution – Endemic to south-eastern D.R. Congo (Haut Katanga).

Habitat – Shaded vertical siliceous rock faces, often on metalliferous rocks, e.g. malachite, or rarely on nonmineralized rocks, 1200–1500 m elevation. Malachite is a copper carbonate hydroxide mineral [Cu 2 CO 3 (OH) 2]. It often results from the weathering of copper ores.

Etymology – Named after the metalliferous rocks which are the preferred habitat.

Additional material examined – D.R. CONGO – Haut Katanga • Chilonge, à 4,5 km au sud de Tenke, affleurement des rochers siliceuses cellulaires; 5 Dec. 1987; Schaijes 3850; BR • Rocks at Chilonge near Tenke, non-mineralized rocky terrain; 10°35′06″S, 26°08′06″E; 1200 m; 11 Apr. 1990; TROPMETEX 206; MO, BR[BR0000016803308] • Luita, affleurement rocheux en pente; 10°44′S, 26°18′E; 1500 m; 4 Apr. 1986; Malaisse 13819; BR[BR0000016803305].

Taxonomic notes – The species is clearly related to Streptocarpus goetzei Engl. ( Engler 1901: 406) and S. compressus B.L.Burtt ( Burtt 1958: 570) which also bear a corolla mouth compressed between the upper lobes so that the opening is shaped like an inverted V ( Hilliard & Burtt 1971). The three species are compared in table 1 . Streptocarpus goetzei is usually confined to forests and is found in southwestern Tanzania (Rungwe Mts), southern Malawi, and northern Mozambique ( Hilliard & Burtt 1971; Darbyshire 2006). The new species is endemic to metalliferous rocks in Katanga (Duvigneaud & Denaeyer-De Smet 1963). It is probably more closely related to S. compressus which is confined to Songea and Iringa Districts in Tanzania, where it grows in open rocky habitats ( Hilliard & Burtt 1971; Darbyshire 2006). Streptocarpus malachiticola is already figured by Malaisse et al. (2016) under the name of Streptocarpus aff. michelmorei B.L.Burtt. A photograph is published on the website http://copperflora.org/eflora/index. php?family= Gesneriaceae under the name of Streptocarpus rhodesianus .

IUCN conservation assessment (preliminary) – Endangered: EN B1+2ab(iii). Streptocarpus malachiticola is restricted to copper-rich rocks of malachite and thus the three identified locations are under potential threat of mining. With an estimated AOO of 12 km 2 (assuming a 4 km 2 grid cell size) and four herbarium specimens from three locations, the most recent being collected in 1990, the species could be preliminarily assessed as Endangered: EN B1+2ab(iii).

Figures

Figure 1 – Streptocarpus malachiticola. A–B. Habit. C. Inflorescence. D. Flower, frontal view. E. Flower, lateral view. F. Stamen. G. Staminode. H. Calyx with ovary, style, and stigma. I. Style and stigma. K. Tip of ovary, style, and stigma. L. Glandular hairs on calyx. M. Tip of sepal with glandular hairs. N. Hairs on pedicel.A, C–K from Malaisse 11427; B from Schaijes 3850. Illustration by Eberhard Fischer.

Figure 2 – Streptocarpus malachiticola. A, C. Habit. B. Inflorescence. D. Flower. Photographs taken by Julie Lebrun, Biodiversity and Landscape Unit, Gembloux Agro-Bio Tech, University of Liège at Tshilongo, Kabwe (A–B: © Julie Lebrun, all rights reserved) and Michel Schaijes at Tenke (C–D: © Michel Schaijes, all rights reserved).

Figure 9 – A. Distribution map of Streptocarpus malachiticola, S. bampsii, and S. salesianorum. B. Distribution map of S. schaijesii and S. malaissei. Map created using ArcMap 10.8 (https://www. arcgis.com). © Esri and its licensors, all rights reserved.