Tuesday, April 24, 2018

[Botany • 2018] Kindia gangan • A New Cliff-dwelling Genus (Pavetteae, Rubiaceae) with Chemically Profiled Colleter Exudate from Mt Gangan, Republic of Guinea


Kindia gangan Cheek

in Cheek, Magassouba, Howes, Doré, Doumbouya, et al​., 2018.
Photos: Martin Cheek.

 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.

Taxonomic Treatment

Kindia Cheek, gen nov.

Type: Kindia gangan Cheek

Diagnosis: differs from Leptactina s.l. in a corolla tube with a slender proximal part and an abruptly much wider, longer distal part (not more or less cylindrical, or gradually widening); a glabrous, winged pollen-presenter (not hairy, non-winged); an epilithic habit (not terrestrial, growing in soil); a conspicuous opaque red colleter exudate (not translucent and colourless or slightly yellow); and type 1 pollen (not type 2) (De Block & Robbrecht, 1998).

Figure 1: Photographs showing the cliff-dwelling habitat and the habit of Kindia 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 1: Photographs showing the cliff-dwelling habitat and the habit of Kindia gangan at Mt Gangan, Kindia, Guinea.
(A) plants scattered on high sandstone cliff (Cheek 18345); (B) plant habit on cliff face (Cheek 18541A).
Photos taken by Martin Cheek.

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

Local names and uses: None are known. The local communities in the area when interviewed in November 2017, stated that they had no uses nor names for the plant (D Molmou & T Doré, pers. obs., 2017).

Etymology: The genus is named for the town and prefecture of Kindia, Guinea’s fourth city, and the species is named for Mt Gangan to its north, which holds the only known location for the species. Both names are derived as nouns in apposition.

Distribution République de Guinée, Kindia Prefecture, northeastern boundary of Mt Gangan area, west of Kindia-Telimélé Rd (Fig. 5).

Ecology: 
The area of the Mt Gangan complex in which we found plants of Kindia consists of two parallel ranges of small sandstone table mountains separated by a narrow N–S valley that appears to be a geological fault. Bedding of the sandstone is horizontal. Uneven erosion on some slopes has resulted in the formation of frequent rock ledges, overhangs and caves. In contrast, other flanks of the mountains are sheer cliffs extending 100 m or more high and wide. It is on the cliff areas at 230–540 m a.s.l that K. gangan occurs as the only plant species present, usually as scattered individuals in colonies of (1–3–)7–15 plants, on the bare expanses of rock that are shaded for part of the day due to the orientation of the cliffs or to overhangs or due to a partial screen of trees in front of the rockfaces. Pitcairnia feliciana (Bromeliaceae), in contrast is found in fully exposed sites where there is, due to the rock bedding, a horizontal sill in which to root. These two species can grow within metres of each other if their cliff microhabitats occur in proximity. The rock formations create a variety of other microhabitats, including vertical fissures, caves, shaded, seasonally wet ledges, and are inhabited by sparse small trees, shrubs, subshrubs, perennial and annual herbs, many of which are narrow endemic rock specialists. We speculate that the seed of this species might be bat-dispersed because of the greenish yellow-white colour of the berries (less attractive to birds than fruits which are e.g., red or black) and the position of the plants high on cliff faces, where nothing but winged creatures could reach them, apart from those few plants at the base of the cliffs. However, fruit dispersal is not always effected since we found numerous old dried intact fruits holding live seeds on the plants at the type locality in February 2016. It is possible that the robust, large white flowers are pollinated by a small species of bat since in June and September we saw signs of damage to the inner surface of the corolla inconsistent with visits by small insects. The damage takes the form of brown spots on the inner surface of the corolla tube. Freshly opened flowers do not have these spots, nor do all flowers, only those few which show slight damage. The very broad, short corolla is not consistent with pollination by sphingid moths (which prefer long, slender-tubed flowers), but this cannot be ruled out.


Conclusions: 
Kindia, an endangered subshrub, restricted to bare, vertical rock faces of sandstone is described and placed in Clade II of tribe Pavetteae as sister to Leptactina s.l. based on chloroplast sequence data. The only known species, K. gangan, is distinguished from the species of Leptactina s.l. by a combination of characters: an 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 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 winged and glabrous; orange colleters, which encircle the calyx-hypanthium, occur at base and inside the calyx and stipules and produce vivid red exudate. 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.


Martin Cheek, Sékou Magassouba, Melanie-Jayne R. Howes, Tokpa Doré, Saïdou Doumbouya, Denise Molmou, Aurélie Grall, Charlotte Couch and Isabel Larridon​. 2018. Kindia (Pavetteae, Rubiaceae), A New Cliff-dwelling Genus with Chemically Profiled Colleter Exudate from Mt Gangan, Republic of Guinea.  PeerJ. 6:e4666. DOI: 10.7717/peerj.4666


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