Kindia (Pavetteae, Rubiaceae), a new cliff-dwelling genus with chemically profiled colleter exudate from Mt Gangan, Republic of Guinea

Abstract

A new genus Kindia (Pavetteae, Rubiaceae) is described with a single species, Kindia gangan, based on collections made in 2016 during botanical exploration of Mt Gangan, Kindia, Republic of Guinea in West Africa. The Mt Gangan area is known for its many endemic species including the only native non-neotropical Bromeliaceae Pitcairnia feliciana. Kindia is the fourth endemic vascular plant genus to be described from Guinea. Based on chloroplast sequence data, the genus is part of Clade II of tribe Pavetteae. In this clade, it is sister to Leptactina sensu lato (including Coleactina and Dictyandra). K. gangan is distinguished from Leptactina s.l. by the combination of the following characters: its epilithic habit; several-flowered axillary inflorescences; distinct calyx tube as long as the lobes; a infundibular-campanulate corolla tube with narrow proximal section widening abruptly to the broad distal section; presence of a dense hair band near base of the corolla tube; anthers and style deeply included, reaching about mid-height of the corolla tube; anthers lacking connective appendages and with sub-basal insertion; pollen type 1; pollen presenter (style head) winged and glabrous (smooth and usually hairy in Leptactina); orange colleters producing a vivid red exudate, which encircle the hypanthium, and occur inside the calyx and stipules. Kindia is a subshrub that appears restricted to bare, vertical rock faces of sandstone. Fruit dispersal and pollination by bats is postulated. Here, it is assessed as Endangered EN D1 using the 2012 IUCN standard. High resolution LC-MS/MS analysis revealed over 40 triterpenoid compounds in the colleter exudate, including those assigned to the cycloartane class. Triterpenoids are of interest for their diverse chemical structures, varied biological activities, and potential therapeutic value.

Keywords: Cliff-dwelling; Conservation; Epilithic; Guinea-conakry; Rubiaceae; Tropical Important Plant Areas.

Figure 1. Photographs showing the cliff-dwelling habitat and the habit of K. gangan at Mt Gangan, Kindia, Guinea.

(A) plants scattered on high sandstone cliff (Cheek 18345); (B) plant habit on cliff face (Cheek 18541A); (C) frontal view of flower (Cheek 18541A); (D) side view of inflorescence showing cupular bract (Cheek 18541A); (E) opened fruit showing ripe seeds (Cheek 18345). Photos taken by Martin Cheek.

Figure 2. Scanning electron micrographs of triangular pollen (unacetolysed) of K. gangan.

(A) polar view; (B) surface sculpturing. From Cheek 18541A.

Figure 3. Summary phylogenetic hypothesis based on the concatenated BI analysis.

Clades I–IV were numbered according to De Block et al. (2015).

Figure 4. K. gangan Cheek.

(A) habit, with indication of bullate leaf surface; (B) plants in situ on rock face (from photograph); (C) adaxial leaf indumentum around midrib; (D) abaxial leaf indumentum around midrib; (E) inner face of stipule at second node; (F) secretory colleter from E; (G) flower, post-anthetic; (H) peduncle and proximal cup of bracts with lobes (sheathing and concealing a smaller distal cup of bracts) below flower; (I) corolla from post-anthetic flower cut longitudinally and opened to display inner surface; (J) stigma; (K) transverse section of mature fruit, empty of seeds but showing placenta (in the left locule); (L) seed, hydrated, lateral view; (M) seed, dry, lateral view; (N) seed, dry, view from above. Scale bars: A, B = 5 cm; G, I, K = 1 cm; H = 5 mm; C, D, E, J = 2 mm; F, L, M, N = 1 mm. Drawn by Andrew Brown based on Cheek 18345.

Figure 5. Map of the distribution of K. gangan.

The distribution of the species was mapped using SimpleMappr.