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| Lebbiea grandiflora Cheek
in Cheek & Lebbie, 2018.
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Abstract
Lebbiea grandiflora (Podostemaceae), a rheophytic herb from the Sewa River rapids in Sierra Leone, is described as a new species. It is the first new African genus of Podostemaceae published for 30 years. First collected in May 2017, the species is assessed as Critically Endangered using the IUCN 2012 standard. It is on the edge of extinction with a small population at a single site threatened by deposition of gravel and sand from alluvial gold and diamond mining upstream, and a planned hydro-electric dam. The new genus is unique in Podostemaceae in a) its highly developed and robust style-stigma structure in which the bases of the two style-stigmas unite to form a bifurcate funneliform-cylindrical structure, with a reflexed, blade-like apex that extends half-way around the perimeter of the ovary-fruit towards the base of the ovary-fruit, b) a specialised andropodium, with robust, self-supporting capacity, having differentiated thickened central, and angled, thinner marginal areas (in other Podostemaceae the andropodial structures are undifferentiated), c) the pillar-like haptera which completely elevate the crustose root above the substrate. Lebbiea is placed in Podostemoideae, necessitating amplification of the delimitation of that subfamily in which it is additionally unique in having the foliose tepals characteristic of the basal subfamilies Weddellinoideae and Tristichoideae.
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| Fig 1. Lebbiea grandiflora. A. habit, whole plant, in fruit, showing the flat root, a pillar-like ‘haptera’, and a shoot with three inflorescences, B. detail of shoot with three branches, C. view of upper surface of a flattened root, with six short, erect shoots, each with 1–2 1-flowered inflorescences emerging from spathellum remains, D. side view of plant showing, on the lower surface of the flattened root, the pillar-like haptera, branched at base; upper surface of root with spathellum-sheathed inflorescence base, E. plant attached to rock by weft of thread-like root hairs (indicated with arrow) from base of pillar-like haptera; upper surface of flattened root with two shoots, F. side view of flower showing one of two tepals in full frontal view, G. as F. with tepal removed, exposing the gynoecium with, to left, the arched-over androecium, H. side view of flower with androecium in centre, two tepals flanking the gynoecium, I. androecium (leftmost of three anthers missing), J. transverse section of andropodium, K. view of gynoecium from above showing funneliform style-stigma base, L. fruit, dehisced, M. transverse section of bilocular fruit, showing septum and placentae, N. placentae with seeds, divided by septum, O. seeds, P. seed with mucilage outer layer.
Drawn by Andrew Brown from Lebbie A2721.
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Lebbiea Cheek gen. nov.
Type: Lebbiea grandiflora Cheek sp.nov.
Diagnosis: differing from all other Podostemaceae in the basally connate style-stigma pair which form a short, bifurcate, funneliform cylinder, the apices of each style-stigma reflexed, forming a keel which encircles the distal perimeter of the ovary (in all other species the stigmas are not divided into basal and distal parts, and if conjoined never form a cylinder, nor have a keel-like distal part); also differing from all other Podostemaceae in the robust, free-standing, concave andropodium, differentiated into thinner marginal and thickened central portions (not depending on hydrostatic pressure to stay erect, not flat or cylindric, undifferentiated); differing from all other Podostemoideae in the ovate, concave, tepals that conceal the ovary (not filiform, inconspicuous) (Fig 1)
Lebbiea grandiflora Cheek sp. nov. [urn:lsid:ipni.org: 77188051-1]
Type: Sierra Leone, Sewa River, between Fomaya (Kenema District) and Ngnawama (Kono District), 257 m alt., fr. 5 May 2017, Lebbie A2721 (holotype K! K000875049; isotypes SL!, US!, ZT!)
Etymology: The generic name Lebbiea commemorates Dr. Aiah Lebbie, Head of The National Herbarium of Sierra Leone, Njala University, Sierra Leone who collected the type and only known material of this genus. The specific epithet refers to the flowers which are the largest known in the family in Africa (4-5 mm long above the pedicel), exceeding even those of Dicraeanthus africanus Engl. (3.5 mm long above the pedicel).
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| The Koukoutamba falls in Guinea on the Bafing River of Guinea-Conakry. With 5 species of Podostemaceae, three globally threatened including two new to science (one of which is Lebbiea), it is the richest site known for Podostem species diversity in Guinea. |
Distribution: Known only from one site on the Sewa River in the Kono and Kenema districts of Eastern Sierra Leone. The nearest settlement is Nɡnawama, several kilometres drive from Jaiama Sewafe, a large settlement dependent on alluvial diamond mining (Fig 2).
Ecology: Lebbiea grandiflora grows on submerged rocks in river beds, in the wet season, where they have been found in the middle of the river and close to the river bank. At the height of the dry season when falling water levels have exposed the rocks, the plants flower and fruit and die off (they can be easily scraped off the rock at this time). They grow in small isolated patches on rocks, covering the horizontal surfaces in a mat-like appearance with the flattened roots. Two of the observed clumps were growing on rocks in the middle of the river, with the third one close to the edge of the bank where a small rapid was still observable at the height of the dry season. The mass of rock on which it was growing had been partly dissected by the erosive forces of the river current, developing numerous small basins in which water was still present, sand and pebbles from the alluvial diamond mining had also settled. In the cracks in the bedrock and at the edges of the numerous basins can be found tufted water grasses growing in association with hydrophytes such as Hygrophila spp. (Acanthaceae). These plants probably serve to modulate the water current over the rocks in the wet season. Pterocarpus santalinoides L'Hér. ex DC. (Leguminosae-Papilionoideae) was the only tree growing on these rocks in the middle of the river.
Martin Cheek and Aiah Lebbie. 2018. Lebbiea (Podostemaceae-Podostemoideae), A New, Nearly Extinct Genus with Foliose Tepals, in Sierra Leone. PLoS ONE. 13(10): e0203603. DOI: 10.1371/journal.pone.0203603
Kew Scientist discovers new species of aquatic herb on the edge of extinction kew.org/science/news/kew-scientist-discovers-new-species-of-aquatic-herb-on-the-edge-of-extinction
