Berlinia korupensis (Leguminosae – Caesalpinioideae), a new tree species from Cameroon
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- Mackinder, B.A. & van der Burgt, X.M. Kew Bull (2009) 64: 129. doi:10.1007/s12225-009-9100-z
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The tree species Berlinia korupensis Mackinder & Burgt is described as new. The species is endemic to the southern part of Korup National Park in Cameroon. Seventeen trees have been found so far, the largest being 42 m high and having a trunk diam. of 88 cm. The new species is assessed as Critically Endangered (CR D) under the criteria of IUCN. Two distribution maps are included; one map indicating the single locality in Cameroon near the Nigerian border where the new species was found and another map of the permanent plot where 14 of the 17 trees were recorded. A line drawing is also included, along with colour photographs of the flowers and the trunk.
Key wordsBerliniaCameroonCaesalpinioideaeFabaceaegregariousKorup National Parknarrow endemic
The southern part of Korup National Park (south Korup) in Cameroon is covered by lowland rainforest. The environment is fairly uniform: the topography is flat or gently sloping and the soils are sandy with a substrate of crystalline rocks. The overall physiography is rather uniform. However, the tree species composition is much less uniform, as many species grow gregariously, that is they are abundant in some parts of the forest but absent in others. Numerous western and central African tree species from the legume subfamily Caesalpinioideae are known to grow gregariously (Aubréville 1968; Letouzey 1968; Wieringa 1999) and in south Korup Tetraberlinia bifoliolata (Harms) Hauman, T. korupensis Wieringa and Microberlinia bisulcata A. Chev. are well documented as doing so (Newbery et al. 1998). At least two caesalpinioid tree species (T. korupensis and Englerodendron korupense Burgt) are endemic to south Korup. Our new species Berlinia korupensis is a third example of a gregarious caesalpinioid tree species that is endemic to the rainforests of south Korup.
In January 2003, during the establishment of a permanent plot in primary lowland rainforest in south Korup, the first trees of the new species were registered. The leaflets and flowers collected from the ground in April that year (later made into the collection van der Burgt & Eyakwe 822) were compared at WAG and given a preliminary identification of Berlinia confusa Hoyle. In April 2005, a flowering collection was made (van der Burgt 756) along with some photographs. On examining the photographs, one of which is shown as Fig. 2A, the first author concluded that the material did not match B. confusa, but instead represented a species new to science. In October 2005, pods were collected from the same tree (van der Burgt 780).
To distinguish Berlinia korupensis in flower from other species, an abbreviated key is provided. Based on relative size of petals, there are three different petal arrangements found in Berlinia, so for ease of use, the first division of the key is a trichotomy.
Abbreviated key based on floral characters to distinguish Berlinia korupensis from other species of Berlinia
1a. Adaxial petal c. 1 – 3 cm longer than the lateral and abaxial petals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b. All petals of subequal length; bracts 45 – 120 mm long . . . . . . . . . . . B. occidentalisKeayor B. bracteosaBenth.
1c. Adaxial petal much longer and wider than the lateral and abaxial petals, the smaller petals not longer than the length of the claw of the adaxial petal; bracts caducous, seldom seen, not exceeding 5 mm long . . . . . . . . . . . . B. auriculataBenth., B. bruneelii (De Wild.) Torre & Hillc., B. confusa, B. congolensis (Baker f.) Keay, B. coriaceaKeay, B. craibiana Benth. B. giorgiiDe Wild., B. grandiflora (J.Vahl) Hutch. & Dalziel, B. hollandiiHutch. & Dalziel, B. lundensisTorre & Hillc., B. orientalisBrenan, B. phenacoaMackinder, B. rabiensisMackinder, B. sapiniiDe Wild., B. tomentellaKeay, B. viridicansBaker f.
2a. Bracts 7 – 12 mm long, falling before anthesis; known only from Cameroon . . . . . . . . . . . . . . . . . B. korupensis
2b. Bracts 22 – 40 mm long, persisting after anthesis; known only from Gabon . . . . B. razziferaMackinder & Wieringa
Berlinia korupensisMackinder & Burgtsp. nov.B. razziferae Mackinder & Wieringa affinis sed bracteis late triangularibus (nec ovatis) minoribus 7 – 12 × 4 – 5 mm (nec 22 – 40 × 14 – 20 mm), multo breviore tempore caducis atque in inflorescentia immatura conspicuis (nec ad anthesin neque post lapsum florum persistentibus), bracteolis tenuis (nec crassis) angustioribis c. triplo longioribus (nec c. duplo tantum longioribus) quam latioribus atque intus partim dense sericeis (nec glabris neque sparse puberulis), ovariis brevioribus c. 7 mm (neque 12 – 15 mm) longis sericeis (nec ± glabris margine pubescenti excepta) vel B. confusae Hoyle affinis sed rachide foliorum sparse vel modice puberulis (nec glabris), venis secundariis et supra et infra visibilibus (nec indistinctis), bracteis triangularibus ad basin 7 – 12 mm (nec 2 mm) latis atque in inflorescentia immature conspicuis (nec inconspicuis in inflorescentiis perjuventibus tantum visis atque mox caducis, pagina interiora bracteolarum omnino glabra (nec partim dense puberula), superficie hypanthia irregulariter pubescenti atque inter vittiis longitudinalibus pilorum manifesta (nec superficie glabra neque pubescentiam sparsam dispersam raro densiorem ferenti), sepalis c. 7-plo (nec c. 5-plo) longioribus quam latioribus, petalis lateralibus atque abaxialibus inter se similibus, omnes 27 – 38 × 8 – 10 mm (nec dissimilibus lateralibus 7 – 17 × 3 – 4 mm, abaxialibus 7 – 12 × 2.5 – 3 mm), atque ad apicem emarginatis interdum in medio sinus lobatis (nec ad apicem integris, ovario c. 7 mm (nec 10 – 12 mm, longo) differt. Typus: Cameroon, SW Province, Korup National Park, NW Plot near P transect, van der Burgt 756 (holotypus WAG; isotypi BR, G, K, MO, P, SCA, YA).
Distribution. Africa: Cameroon.
habitat & ecology. Primary rainforest on well-drained sandy soil; c. 100 m. The rainfall at the Bulu weather station, c. 12 km SE of the type locality, ranged from 4023 to 6146 mm/y, and averaged 5061 mm/y (1984 – 2007). The climate is strongly seasonal with one distinct dry season from December to February (average monthly rainfall less than 100 mm).
Berlinia korupensis has only been found within and near to the “NW plot”, which occupies an area of 56.25 ha and is situated near the “P transect” in the Caesalpinioideae-rich forest of south Korup. It is absent from the nearby “P plot”, which occupies an area of 82.5 ha and is situated just SE of the NW plot, in the same forest type. The species is also absent from the 50 ha “KFDP plot” (Kenfack et al. 2006), which is situated in Caesalpinioideae-poor forest at 11 km to the northeast of the P and NW plots, but still within Korup National Park.
As is the case for all species of Berlinia, and indeed many other caesalpinioid genera, the seeds of B. korupensis are dispersed by explosive pod dehiscence (van der Burgt 1997). When a mature pod is exposed to sunshine or dry air, it begins to dry. The two drying valves of the pod are predisposed to curl up in different directions, and as a result tension builds up between them. The corky connecting layer between the two valves keeps them attached and thereby flat, but as the drying continues, the tension eventually becomes too large and the pod dehisces suddenly and forcefully. The two valves twist rapidly, in opposite directions, and the seeds are ejected at speed. Many seeds drop beneath the crown of the parent tree, but some are dispersed to short distances from the edge of the crown. The maximum explosive dispersal distance is unknown but we speculate that it is probably in the range of 30 – 50 m. It is also unknown if there is any secondary dispersal e.g. by animals or by rivers. The relatively short and strictly limited maximum explosive dispersal distance is presumed to be a contributory factor to grove-formation (Wieringa 1999).
Conservation. Berlinia korupensis is assessed here as Critically Endangered (CR D) under the criteria of IUCN (2001). This species is known from only 17 individuals at a single location within a protected area.
Etymology. Named after Korup National Park within which all known individuals of this species are located.
Notes. A striking feature of the flowers of van der Burgt 756 is the size of the lateral and abaxial petals which are neither as long as the well-developed adaxial petal (as is the case in Berlinia occidentalis Keay and B. bracteosa Benth.) nor very much shorter (as is the case in the majority of Berlinia species). In B. korupensis the abaxial and lateral petals are intermediate in size between these extremes. B. razzifera is the only other species in the genus that possesses the intermediate petal form.
Formerly two generic sections were recognised within the genus but as a consequence of the recent discovery and description of new species, especially Berlinia razzifera and now B. korupensis justification of two sections based on gross morphology has become untenable. In particular, the combination of morphological characters presented by these two species has eroded the distinction between the two sections. Furthermore, the results of a phylogenetic analysis based on nucleotide sequence data of the Internal Transcribed Spacer region (unpublished data) failed to recover the morphologically delimited sections and so they are no longer upheld.
The functionality of these flowers is hypothesised here as the viability of the pollen is not known.
The authors would like to thank Prof. David Newbery of the Institute of Plant Sciences, University of Bern, who supervised the ecological research that lead to the discovery of the present new species. The field research was funded by the Swiss National Science Foundation (Grant 3100-066655 to Prof. Newbery), and coordinated by Dr G. Chuyong. Three funds of the Royal Botanic Gardens, Kew, the Donations fund, the OFC fund and the Bentham-Moxon fund, also funded the collection of specimens and data. We thank the Cameroon government for permission to carry out research in Cameroon, and Korup National Park (Conservator, A. Kembou) for access to the site. We also thank the National Herbarium of Cameroon (Head, J.-M. Onana) for cooperation. Moses Elangwe climbed the tree from which the holotype was collected. Wolfgang Bischoff, Motoh Jackson, Sylvanos Njibili and Charles Okha provided field assistance. We would also like to thank Margaret Tebbs for preparing the illustration and Melanie Thomas for translating the Latin diagnosis.