Lachenaud, O., Q. Luke & B. Bytebier (2017). Keetia namoyae (Rubiaceae, Vanguerieae), a new species from eastern Democratic Republic of Congo. Candollea 72: 23–26. In English, English and French abstracts.
A new species of Rubiaceae from the Democratic Republic of Congo, Keetia namoyae O. Lachenaud & Q. Luke, is described and illustrated. The species resembles Keetia tenuiflora (Hiern) Bridson and Keetia mannii (Hiern) Bridson, but differs from both in having alternate (not opposite) flowering twigs with stiff appressed hairs, few-flowered inflorescences, a longer corolla tube, and larger fruits. The species is only known from the type locality in Maniema Province, and is assessed to be “Critically Endangered” according to IUCN Red List Categories and Criteria.
Introduction
The genus Keetia E.P. Phillips (Rubiaceae, Vanguerieae) was for a long time included in Canthium Lam., before Bridson (1986) resurrected it for a group of African species. Keetia currently includes 32 species, occurring in most of sub-Saharan Africa, except in arid regions. The East African species have been revised by Bridson (1986, 1991) but no recent taxonomic revision exists for West and Central Africa. As a result, the genus is taxonomically poorly known, and the number of species certainly underestimated. Keetia has some potential interest as a source of medicinal compounds. Recent studies on K. leucantha (K. Krause) Bridson, which is used in traditional medicine in Benin, found significant antiplasmodial, antitrypanosomial and antileishmanial activity of leaf and twig extracts in in vitro conditions (Bero et al., 2009,2011). Most of the other Keetia species have not yet been tested pharmacologically, and it would be highly interesting to know if they show similar properties.
In 2008, two of us (BB and QL) collected a Rubiaceae specimen in Maniema Province, Democratic Republic of Congo, which the first author identified as a new species. This collection clearly belongs to the tribe Vanguerieae, due to the inflorescences in paired axillary cymes, exserted anthers, exserted style with a conspicuously hooded stigma, and indehiscent fruits with 1-seeded locules. Within this group, it shows all the characters typical of Keetia (Bridson 1986) : sarmentose habit, stipules interpetiolar and caducous, stigma longer than broad, anthers erect and subsessile in the corolla throat, and 2-locular fruits ; only the presence of a lid-like area at the apex of the pyrenes, considered typical of the genus, could not be verified, because the fruits are too few for a dissection to be made.
Despite a thorough search among unidentified specimens of Keetia and related genera in BR (where most herbarium collections from D.R. Congo are deposited), BRLU, K, P and WAG, no similar collections were found. It thus appears that the species is very rare, and presumably a local endemic. It is here described as Keetia namoyae O. Lachenaud & Q. Luke, and its affinities and conservation status are discussed.
Taxonomy
Keetia namoyae O. Lachenaud & Q. Luke, spec, nova (Fig. 1).
Typus : Democratic Republic of Congo. Prov. Maniema: Namoya, Mwendamboko Hill, 4°00′05″S 27°32′94″E, 12.IV.2008, fl. & fr., Bytebier & Luke 2796 (holo-: BR [BR000000524731]!; iso-: EA!).
Foliis glabrescentibus et coriaceis venulis tertiariis inconspicuis K. tenuiflorae (Hiern) Bridson et K. mannii (Hiern) Bridson similis, sed ab ambabus speciebus conspicue differt ramis floriferis alternis (nec oppositis) cum indumento sparso et valde appresso, inflorescentiis paucifloris, floribus majoribus corollae tubo c. 4 mm longo (nec c. 2 mm) fructibusque majoribus c. 20 × 20 mm apice paullo emarginatis.
Scandent shrub to 2 m high, with branches alternate and directed backwards, subtended by normal (not modified) leaves. Twigs rather sparsely covered with very stiffly appressed hairs, which persist for a long time on the woody, medium brown bark. Stipules c. 2 mm long, shortly triangular with apex laterally compressed, with same indumentum as twigs, very soon caducous. Leaves with petiole 4–7 mm long, stiffly appressed-pubescent ; blade elliptic, acute at base, acuminate at tip, 4–9 × 2.2–4 cm, very coriaceous, glabrous above, sparsely appressed-pubescent on midrib beneath, drying dull brownish-green with underside paler ; lateral nerves 4–6, not strongly prominent ; tertiary veins invisible or almost so; small tuft-domatia present in axils of lateral nerves along midrib. Inflorescences cymose, 10–15-flowered, c. 1.5 cm long including c. 0.5 cm long peduncle, shortly branched, sparsely pubescent. Bracts small, c. 1.5 mm, triangular and acute at apex, ciliate. Flowers (4-)5-merous ; pedicels 2–5 mm, densely appressed-pubescent. Calyx split almost to the base into narrowly triangular teeth c. 0.75 mm long, shortly ciliate on the margin. Corolla cream ; tube cylindrical, 4 × 1.5 mm, glabrous outside, hairy inside with a ring of long (c. 1 mm) abruptly deflexed hairs near the lower l/4th, and short sparse hairs above reaching just under the throat ; lobes 2 mm long, reflexed, glabrous. Flower buds cylindrical with a rounded head.Anthers almost completely exserted, erect, c. 1 × 0.5 mm. Disk shortly pubescent. Style glabrous, exceeding throat by 3 mm and ending in a hood-like stigma c. 0.7 mm long. Fruit slightly obovate, 20 × 20 mm, rounded at base, very shallowly emarginate at apex, glabrous ; pedicel reaching c. 8 mm.
Etymology. — The species is named after its only known locality.
Distribution and ecology. — Keetia namoyae is only known from the type locality in Maniema Province, eastern D.R. Congo (Fig. 2). It was found only once in disturbed, open secondary rain forest, at an altitude of 977 m. The following species were recorded in the vicinity: Adenia tricostata De Wild., Aidia micrantha (K. Schum.) F. White, Aptandra zenkeri Engl., Argomuellera pierlotiana J. Léonard, Boehmeria macrophylla Hornem., Celosia globosa var. porphyrostachya C.C.Towns., Crassocephalum rubens (Jacq.) S. Moore, Cyperus distans L.f., Dichapetalum sp., Dichapetalum parvifolium Engl., Dioscorea sp., Monanthotaxis sp., Justicia tenella (Nees) T. Anderson, Lindackeria schweinfurthii Gilg, Macaranga sp. nov. (Bytebier & Luke 2805), Puelia ciliata Franch.,Rhabdophyllum welwitschii Tiegh., Rutidea insculpta Bridson, Solanum welwitschii C.H. Wright, Spermacoce exilis (L.O. Williams) W.C. Burger & C.M. Taylor, Thecacoris lucida (Pax) Hutch, and Tricalysiapallens Hiern.
Conservation status. — This plant is known from a single location sensu IUCN (2012) ; the extent of occurrence is therefore not calculable, and the area of occupancy is estimated as 4 km2. It was collected on a hill that was due to be mined for gold ; a decline in the area of occupancy, habitat extent and quality, number of locations and number of individuals is therefore expected. No other individuals are known, although the area has several other hills and is at the edge of extensive primary forest. The species is therefore assessed to be “Critically Endangered” [CR B2ab(ii,iii,iv,v)+D1] of the IUCN (1991).
Notes. — Keetia namoyae is a rather distinctive species due to its very large fruits, small coriaceous leaves with inconspicuous tertiary venation, and twigs with sparse and very stiffly appressed hairs. Due to the appressed-pubescent twigs and lack of conspicuous tertiary veins, K. namoyae most closely resembles K. tenuiflora (Hiern) Bridson and some forms of K. mannii (Hiern) Bridson (the latter usually has glabrous twigs, but occasional variants with pubescent twigs occur). However, these two species differ from K. namoyae in many characters, including : flowering twigs opposite, with indumentum not so stiffly appressed; flowers more numerous (at least 25 per inflorescence, often more) and distinctly smaller, with corolla tube c. 2 mm long only; fruits smaller, < 12 mm long, frequently 1-seeded, or if 2-seeded then strongly bilobed. Keetia tenuiflora further differs from K. namoyae in having a pale buff-grey bark.
Although Bridson (1991: 921) described the fruits of K. tenuiflora as “1.2–1.5 cm long, 2 cm wide”, this appears to be erroneous ; the largest fruits we have seen in this species are 12 mm long and 17 mm wide.
Acknowledgements
We are grateful to Antonio Fernandez for his drawing of this new species. BB and QL would like to thank the management of Banro Congo Mining Sarl for their support during the survey and acknowledge the cheerful company of the local guides whilst in the field. They would also like to thank Caroline Henderson and SRK Consulting (SA), South Africa, for the opportunity to contribute to the Environmental and Social Impact Assessment. Martin Callmander and Petra De Block are thanked for their comments on a first version of this paper.
