The Orchid Flora of the Mbam Minkom Hills (Yaoundé, Cameroon)

Home , Ancistrochilus, Bulbophyllum, Calyptrochilum, Cheirostylis, Rangaeris

THE ORCHID FLORA OF THE MBAM MINKOM HILLS (YAOUNDÉ, CAMEROON)

Murielle SIMO1, Vincent DROISSART2,5, Bonaventure SONKÉ1,2 and Tariq STÉVART2,3,4,* 1 Laboratoire de Botanique systématique et d’Écologie, Département des Sciences Biologiques, École Normale Supérieure, Université de Yaoundé I, B.P. 047, Yaoundé, Cameroun 2 Herbarium et Bibliothèque africaine, Université Libre de Bruxelles - ULB, 50 Av. F. Roosevelt, CP 169, 1050 Bruxelles, Belgique 3 Missouri Botanical Garden, Africa & Madagascar Department, P.O. Box 299, 63166–0299, St Louis, Missouri, USA 4 National Botanic Garden of Belgium, Domein van Bouchout, B-1860 Meise, Belgium 5 Present address: Institut de Recherche pour le Développement (IRD°, UMR AMAP, Botanique et Bioinforma- tique de l’Architecture des Plantes, Bd de la Lironde, TA A51/PS2, 34398 Montpellier cedex 5, France (* Author for correspondence; e-mail: [email protected]) Received 27 August 2008; accepted 10 July 2009.

ABSTRACT. — Despite its tremendous biodiversity, which results from a strong elevation gradient and high habitat diversity, the fl ora of the Mbam Minkom Hills (Cameroon) is poorly documented. Moreover, these hills have recently become an urgent and major challenge for conservationists because their proximity to the city of Yaoundé has considerably increased human pressure on this area considered as the last main block of primary submontane forest around this city. As a consequence, the main objectives of this paper are to provide the fi rst orchid account of the Mbam Minkom Hills, to document the ecology and the distribution of these species and to highlight the importance of this family for the conservation of this threatened ecosystem. A total of 75 orchid taxa within 27 genera were found in the Mbam Minkom Hills. Sixty-one (81%) were epiphytic, 11 (15%) were terrestrial and 3 (4%) were lithophytic. Six of them (8%), one Bulbophyllum, one Diaphananthe, one Polystachya, one Rhipidoglos- sum and two Stolzia are new taxa. Genera with the highest number of taxa were Polystachya (19 taxa) and Bulbophyllum (12 taxa). Polystachya carnosa is newly recorded for Cameroon. Lowland forest (51 taxa) and inselbergs (29 taxa) are the two habitats with the highest species richness. Species fl ower mainly between March and May and between July and September. Thirty-four (45%) taxa were endemic or near endemic to the Guineo-Congolian regional centre of endemism, of which 14 (19%) were endemic to the Lower Guinean Domain. Moreover, Bulbophyllum teretifolium, Bulbophyllum sp. nov., Cheirostylis divina var. ochyrae, Polys- tachya sp. nov. and Stolzia repens var. cleistogama are endemic to Cameroon. According to IUCN criteria, 50 taxa (67%) are least concerned (LC), 4 (5%) are vulnerable (VU) and 1 (1%) is near threatened (NT). Three taxa (4%), Cheirostylis divina var. ochyrae, Diaphananthe bueae and Polystachya letouzeyana are endangered (EN). Seventeen taxa (23%) are not evaluated (NE). The orchid fl ora of Cameroon is far from being completely known, as shown by the six new taxa and the new national record found during this study.

KEY WORDS. — Orchidaceae, conservation status, epiphytes, inselberg, Lower Guinea Domain, submontane forest. 112 BELGIAN JOURNAL OF BOTANY 142

INTRODUCTION of increasing priority because of the ongoing effect of human activities (TCHOUTO 2004). The Mbam With a number of species estimated to 25 000 Minkom Hills ecosystem is probably one of the (GOVAERTS et al. 2007), orchids are one of the most endangered of Cameroon, and is the last block largest families of fl owering plants. Most species of primary submontane forest around Yaoundé. Its are found in the tropics, the New World tropics tremendous biodiversity (SONKÉ et al. 2006), the being the most diverse (PRIDGEON 1992). Because lack of conservation status, and the important of their reputed beauty and important specifi c human pressure due to the proximity of the city of richness in the tropics, orchids are a major com- Yaoundé (DROISSART & STÉVART 2004, SONKÉ & ponent of conservation policies. Orchids are STOFFELEN 2004) make it one of the main chal- threatened by habitat loss, particularly because lenges for conservationists in Cameroon. many species are epiphytic, or by the avoidance The objectives of this study are, therefore, to of eutrophicated soils for the terrestrial species provide the fi rst specifi c and extensive account of (PILLON & CHASE 2007). In addition to the epi- orchids occurring in the Mbam Minkom Hills, to phytic habit, endemism leads to high vulnerability document the ecology and the distribution of or extinction through habitat loss, as the destruc- these species and to highlight the importance of tion of habitat in one area results in the loss of the the hills for orchid conservation in Cameroon. species (WHITMORE & SAYER 1992, PRIMACK 1993). It seems likely that such extinctions have already been widespread, although the species MATERIAL AND METHODS may not always have been documented (WHIT- MORE & SAYER 1992). STUDY SITE In Cameroonian tropical rainforest, most This study was conducted in the Mbam Minkom orchids are epiphytes (ZAPFACK & ENGWALD Hills, which lie 20 km NW of Yaoundé (3°52’ – 4° N 2008) and are mainly found in the canopy of low- and 11°20’ – 11°27’ E) and cover an area of approxi- land and submontane forests, or sometimes on the mately 100 km2 (Fig. 1). The area possesses the highest rock of inselbergs (facultative epiphytes). The elevation of the Centre Province of Cameroon with an ‘Flore du Cameroun’ lists 360 orchid species in altitudinal range of 600 to 1295 m. Primary vegetation Cameroon (SZLACHETKO & OLSZEWSKI 1998, is lowland and submontane forest. Several inselbergs 2001a,b) but the orchid fl ora is still far from being are also present in the area. completely known. These authors also listed Orchids were collected in summit forest as well as on both east-facing and west-facing slopes of the many species that had not yet been recorded in Mbam Minkom Hills. Because they are exposed to the this country but collected in adjacent countries. In monsoon winds, the west-facing slopes receive more order to fi ll this gap, several publications on the rain (KUETE 1977). This climatic contrast results in pro- fl ora of Cameroon including orchids have recently nounced differences in the physiognomy and fl oristic been published (CRIBB 1998, CRIBB et al. 2000, composition of the forests covering both sides. The STÉVART 2003, CRIBB & POLLARD 2004, POLLARD west side is characterized by an uneven relief and steep et al. 2004, DROISSART et al. 2006, DROISSART et slopes, and is covered by lowland forest, interspersed al. 2009a). However, none of these papers dealt with cultures and fallow land. The east versant is more with the orchid fl ora of the Mbam Minkom Hills. degraded than the west versant and is characterized by The only publications mentioning orchid records its gentle slopes and lowland forest. The summit forests are characterized by a striking physiognomic and fl oris- from the Mbam Minkom Hills (SZLACHETKO & tic homogeneity. The vegetation of the Mbam Minkom OLSZEWSKI 1998, 2001a,b, DROISSART & STÉVART Hills has previously been investigated by LETOUZEY 2004) list nine taxa identifi ed to species (six), (1968), KUETE (1977), ACHOUNDONG (1985, 1996) and subspecies (one) or varieties (two). NOUMI (1998). Studies on the Rubiaceae family carried In Cameroon, ecosystems that harbour most out by SONKÉ & STOFFELEN (2004), SONKÉ et al. (2006) of the rainforest biodiversity are a source of great and NGUEMBOU (2006) revealed the presence of many concern and their conservation has become an issue species endemic to Cameroon. ORCHIDS OF THE MBAM MINKOM HILLS (CAMEROON) 113

Fig. 1. Topographic map of studied area and localisation of different hills (triangle) surrounding Yaoundé (Camer- oon). Collections sites are showed by stars. Floristic data were collected during 44 days in 51 sites.

FLORISTIC DATA RESULTS Floristic data used in this study were gathered from recent fi eld inventories (244 fertile specimens), literature FLORA (nine specimens) and examination of previous herbar- The fl ora of the Mbam Minkom Hills ium collections (eight specimens from YA). For each includes 75 taxa of orchids distributed in 27 gen- species, we determined: the habitat, the elevation range, the phenology based on fi eld and cultivation observa- era, of which 61 (81%) are epiphytic, 11 (15%) tions, the IUCN Red List Categories (2001) taken from are terrestrial and 3 (4%) are lithophytic (Table the literature (CRIBB et al. 2000, CRIBB & POLLARD 2004, 1). Stolzia grandifl ora P.J.Cribb subsp. lejolyana POLLARD et al. 2004, DROISSART et al. 2006) and the Stévart, Droissart & Simo and Stolzia repens phytogeographical status supplied by Kew Monocot (Rolfe) Summerh. var. cleistogama Stévart, Checklist (GOVAERTS et al. 2007) using White’s choro- Droissart & Simo are abready published (DROIS- logical classifi cation (WHITE 1979, 1983). SART et al. 2009b). Bulbophyllum sp. nov., Field data were collected from March 2004 to Diaphananthe sp. nov., Polystachya sp. nov. and March 2007. During our fi eldwork, sterile living plants Rhipidoglossum sp. nov. will be published else- were collected and put in culture in a shadehouse built in where. The most represented genera are Polys- Yaoundé in order to obtain accurate identifi cation based tachya Hook. (19 taxa), and Bulbophyllum on fl owered specimens. For this study, identifi cation was thus improved by ex-situ cultivation of 574 living speci- Thouars (12 taxa). mens, which yielded the 244 fertile specimens. For some Polystachya carnosa P.J.Cribb & Podz. is a fertile specimens, in addition to herbarium specimens, new national record for Cameroon while Bulbo- we collected silica-dried material for molecular studies. phyllum teretifolium Schltr., Bulbophyllum sp. 114 BELGIAN JOURNAL OF BOTANY 142 LowFor Insel SubFor Chorology status DSS 373 E NE X Wide DSS 815 E LC *** X GCR Sub end DSS 387 E LC *** X GCR Sub end DSS 581Simo 4 E LC *** E LC *** X X X Wide Linking GCR-ZAM Droissart & Simo 214 E VU **** X GCR-LG DSS 394Simo 3 E LC *** E X NE X GCR-LG GCR- LGUG Droissart 83 E LC *** X Linking GCR-SOM Droissart & Simo 211 Droissart & Simo 211 T LC *** X GCR Sub end SDS 2434 E LC *** X GCR- LGUG Droissart 3 E LC *** X GCR Sub end DSS 880 E NE X GCR-LG DSS 447 DSND 185 Droissart 1 E E LC *** LC *** L LC *** X X X X X GCR Sub end Wide Wide Droissart 66 E LC *** X Wide DSND 124 E NE X GCR Sub end DSS 644 E LC *** X Linking GCR-SOM Droissart 12 E LC *** X GCR DSS 990 E LC *** X GCR Droissart 5 E VU **** X GCR-LG DSS 389 E NE X Wide DSS 1025 E LC *** X X Linking GCR-ZAM Liv. specLiv. E LC ***** X Wide DSS 412 E LC *** X Linking GCR-SOM Dang 752 T EN **** X GCR-LG Szlach. & bidenticulatum ochyrae (Schltr.) J.J.Verm. (Schltr.) stenopetalum (Kraenzl.) J.J.Verm. ssp.

falcatum O’Brien J.J.Verm. ssp. J.J.Verm. curvicalcaratum (Rchb.f.) Summerh. calyptratum (Rchb.f.) Schltr. (Lindl.) Summerh. (Lindl.) Summerh. liforme var. ﬁ

Summerh. Lindl. melinostachyum (Guinea) Summerh. var. (Rolfe) Schltr. var. (Afzel. ex Sw.) Schltr. (Afzel. ex Sw.) Kraenzl.

Kraenzl. var. Ridl. var. Ridl. var. (Hook.f.) Rchb.f. Schltr. Rchb.f. Schltr. Lindl. (Kraenzl.) Summerh. Rendle (Sw.) Lindl. (Sw.) (Lindl.) Rchb.f. var. (Lindl.) Schltr. (Rendle) Summerh. Lindl. sp. nov.** List of 75 Orchids present in the Mbam Minkom Hills with reference specimens. Species Reference specimen LF Conservation Aerangis collum-cygni Ancistrochilus rothschildianus rothschildianus Ancistrochilus Ancistrorhynchus capitatus Ancistrorhynchus A. metteniae Angraecum distichum A. egertonii Olszewski A. eichlerianum Bolusiella batesii B. talbotii Brachycorythis macrantha Bulbophyllum bidenticulatum B. calyptratum B. B. falcatum B. fuscum B. lupulinum B. oreonastes B. oxychilum B. pumilum B. resupinatum B. sandersonii (Kraenzl.) J.J.Verm. B. teretifolium B. teretifolium Calyptrochilum christyanum Calyptrochilum C. emarginatum C. emarginatum Chamaeangis odoratissima C. vesicata Cheirostylis divina Cheirostylis Szlach. & Olszewski 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Table 1. Table ORCHIDS OF THE MBAM MINKOM HILLS (CAMEROON) 115 LowFor Insel SubFor Chorology X X GCR Sub end status ****** SDS 2431 Droissart 15 T E LC *** LC *** X X X — Pal Wide GCR- LGUG DSND 309 Droissart 13 E E LC *** LC *** X X GCR Sub end Wide DSS 424 EA1c+2c EN DSND 111 DSND 111 E LC *** X X X GCR Sub end DSS 370 E NE X GCR-LG Satabié 795 Droissart 44 T LC *** T NE X X X — Pan Wide Linking GCR-SOM Letouzey 11641 Letouzey 11641 T LC *** X Wide DSS 894 E LC *** X Wide Droissart & Simo 210 T LC *** X Wide Droissart & Simo 220 T LC *** X — Pan Wide Droissart 73 E LC *** X Wide DSND 55 T LC *** X — Pan Wide Dang 672 T NE X Wide Liv. spec.Liv. DSS 423 E LC *** E LC *** X X X GCR Wide Simo 5Simo 2 E LC *** E *** NT X X X Wide GCR Droissart 55 L VU **** X GCR-LG Droissart & Simo 209 E LC *** X X GCR Sub end DSS 381 E LC *** X X X GCR Sub end DSS 363DSS 395DSS 409 E NE E LC *** E VU **** X X X X X X GCR-LG — Pal Wide GCR-LG Simo 1 E LC *** X — Pal Wide DSS 814 E NE X GCR-LG DSND 257 E LC *** X Wide Droissart 18 E EN **** X GCR-LG var. caudatus var. adansoniae nervosa ora ﬂ (Summerh.) Stévart var.

calluni (Lindl.) Summerh. Rchb.f. (Lindl.) Lindl. Thouars polyphylla (Hook.f.) Schltr. albescens (Afzel. ex Sw.) Schltr. (Afzel. ex Sw.) (Afzel. ex Sw.) Lindl. (Afzel. ex Sw.) (D.Don) Lindl. (Rchb.f.) Rchb.f. ex Bateman (Sw.) Kuntze (Sw.) (Rchb.f.) Garay & P.Taylor P.J.Cribb Rchb.f. (Thunb.) Lindl. ssp. Rchb.f. Szlach. & Olszewski (Thouars) Lindl. ex Spreng. Kraenzl.var. Rchb.f. (Thouars) Lindl. (Lindl.) Schltr. Ridl. ssp. Ridl. ssp. P.J.Cribb & Podz.* P.J.Cribb Rchb.f. Kraenzl. ora (Schltr.) Schltr. (Schltr.) ﬂ Lindl. nov. ** nov. nov.** nis ﬁ Species Reference specimen LF Conservation Corymborkis corymbis Cribbia confusa chailluana Cyrtorchis Diaphananthe bidens D. bueae D. pellucida D. sp. Epipogium roseum Epipogium roseum Eulophia euglossa E. odontoglossa Graphorkis lurida Habenaria procera Habenaria procera Liparis nervosa L. tridens Oeceoclades maculata O. saundersiana Plectrelminthus caudatus Plectrelminthus Polystachya adansoniae af P. P. albescens P. albescens P. P. calluni P. P. caloglossa P. P. carnosa P. P. cultriformis P. elegans P. fusiformis P. P. sp. P. P. golungensis P. P. letouzeyana P. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 116 BELGIAN JOURNAL OF BOTANY 142

OLLARD uinea, GCR- & P ion / GCR, Wide Wide ion / GCR, – Congolian), RIBB or = Submontane forests; = from C : EN = Endangered, LC Least LowFor Insel SubFor Chorology 2000, DSS = Droissart, Stévart & Simo, SDS Stévart, status et al.

owered yet = Liv. spec. owered yet = Liv. ﬂ RIBB 2004, ****** = C DSND 83 E NE X Wide Droissart 61 E LC *** X Wide DSS 386 E LC *** X Linking GCR-SOM DSS 840 E LC *** X Wide Droissart & Simo 218 E LC *** X Wide DSS 410DSS 746 E LC *** E LC *** X X Wide Wide Droissart 17 E LC *** X Linking GCR-ZAM DSS 805Droissart 74 E E NE NE X X GCR- LGUG Wide DSND 90 E NE X GCR-LG Droissart 45 E NE X GCR-LG Droissart 68 E NE X GCR-LG DSS 812 E LC *** X Wide Droissart 63 E NE X Wide DSS 433 L NE X X GCR-CLG Liv. spec.Liv. E LC *** X Wide SDS 2415 T LC X Wide et al.

OLLARD

Stévart, Stévart, lejolyana Garay cleistogama 2006, ***** = from P (Rchb.f.) Summerh. var. et al.

(Rchb.f.) Summerh. odorata P.J.Cribb subsp. P.J.Cribb Rolfe (Rchb.f.) Summerh. ROISSART ora ﬂ Kraenzl. (Sw.) Rolfe (Sw.) Kraenzl. (Harv.) Schltr. (Harv.) Lindl. (Szlach.) Szlach. & Olszewski Rchb.f. Lindl. var. (Rchb.f.) Schltr. (De Wild.) Schltr. (De Wild.) (Rolfe) Summerh. var. (Rolfe) Summerh. var. grandi

nov.** Species Reference specimen LF Conservation P. modesta P. P. odorata P. P. paniculata P. P. polychaete P. P. tenuissima P. P. tessellata P. Rangaeris muscicola R. rhipsalisocia Rhipidoglossum curvatum (Rolfe) R. rutilum R. sp. Droissart & Simo. Stolzia Droissart & Simo. S. repens anthomaniaca Tridactyle anthomaniaca Tridactyle T. gentilii T. T. lisowskii T. T. tridentata T. Zeuxine elongata 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 Droissart & Simo, DSND = Droissart, Stévart, Nguembou Djuikouo, Living specimen not 2004, **** = from D Notes. LF, life form: E = epiphyte, L = lithophytic, T = terrestrial; conservation status according to IUCN Red List Categories T = lithophytic, life form: E = epiphyte, L Notes. LF, SubF habitat: LowFor = Lowland forests, Insel Inselbergs, Vulnerable; VU = = Near threatened, concerned, NE = Not evalued, NT chorology: GCR = Guineo Congolian wide, Sub end subendemic, GCR-LG endemic to Lower G LGUG = Guineo Congolian linking species (Lower Guinea – Upper Guinea), GCR-CLG Linking GCR-ZAM = Regional linking species Zambezian Region / GCR, GCR-SOM Somalia Masai Reg = Tropical Africa wides, Wide — Pan = Pantropical wides, Wide – Pal = Paleotropical wides), * new record, ** taxa, *** Wide — Pan = Pantropical wides, Wide Africa wides, Tropical = ORCHIDS OF THE MBAM MINKOM HILLS (CAMEROON) 117 nov., Cheirostylis divina var. ochyrae Szlach. & taxa were found only in lowland forests while 15 Olszewski, Polystachya sp. nov. and Stolzia repens taxa were restricted to inselbergs (Fig. 2). Thir- var. cleistogama are endemic to Cameroon. teen taxa were collected in submontane forests, of which 6 were only encountered there (Table 1). ECOLOGY AND DISTRIBUTION Most orchids collected in the fi eld and in the shadehouse fl ower from March to May and from Species richness was highest in lowland for- July to September. Few species fl ower between ests (51 taxa) and inselbergs (29 taxa). Thirty-nine December and February (Fig. 3).

Fig. 2. Speciﬁ c richness in the Mbam Minkom Hills and in the three main habitats (lowland forest, inselbergs and submontane forest) encountered in this area. Restricted species are those only collected in the under mentioned habitat. Ground species = terrestrials and the lithophytes, Epi = epiphytes.

Fig. 3. Flowering of orchids and mean monthly precipitations of the Mbam Minkom Hills. Data from the meteo- rological station of the military airport of Yaoundé (1997-2006). 118 BELGIAN JOURNAL OF BOTANY 142

According to White’s chorological classiﬁ ca- CONSERVATION tion (WHITE 1979, 1983), 34 taxa are Guineo-Con- According to the IUCN Red List Categories golian endemic / subendemic, 8 are regional link- (IUCN 2001), 50 (67%) of the taxa recorded ing species (species present in two regional centres from the Mbam Minkom Hills are least con- of endemism) and 33 are present in at least three cerned, 1 (1%) is near threatened and 17 (23%) regional centres (wide species, Table 2, Fig. 4). are not evaluated (Fig. 5). Seven taxa (9%) are Five taxa are present in the Guineo-Congolian threatened: Cheirostylis divina (Guinea) Sum- regional centre and the Somalia-Masai regional merh. var. ochyrae, Diaphananthe bueae (Schltr.) centre and 3 in the Guineo-Congolian regional cen- Schltr. and Polystachya letouzeyana Szlach. & tre and the Zambezian regional centre. Inside the Olszewski are endangered while Angraecum Guineo-Congolian regional centre, 11 taxa (19%) egertonii Rendle, Bulbophyllum teretifolium, are endemic to the Lower Guinean Domain. Four Polystachya albescens Ridl. subsp. polyphylla taxa are restricted to the Upper Guinean and Lower (Summerh.) Stévart and Polystachya elegans Guinean Domains and 1 is restricted to the Congo- Rchb.f. are vulnerable (Table 1). lian Domain and the Lower Guinean Domain.

Table 2. Distribution of the 75 taxa recorded in the Mbam Minkom Hills (abbreviation given in Table 1).

Chorological elements Number and % of taxa 1 Guineo Congolian endemic / subendemic 34 (45%) 1a Guineo Congolian wide 4 (5%) 1b Two Domains (linking species) 8 (11%) 1b1 LGUG 4 (5%) 1b2 LGC 1 (1%) 1c Endemic to LG 14 (19%) 1d Sub/near endemic or Marginal Intruder 11 (15%) 2 Regional linking species 8 (11%) 2a Somalia Masai Region / GCR 5 (7%) 2b Zambezian Region / GCR 3 (4%) 3 Wides 33 (44%) 3a Africa wides 27 (36%) 3b Paleotropical 3 (4%) 3c Pantropical 3 (4%)

DISCUSSION ered yet and, therefore, cannot be accurately identifi ed. Orchid specifi c richness of Mbam FLORA Minkom might be similar to that of Mount Oku and the Bali Ngemba Forest Reserve (Table 1), With 75 taxa reported over 100 km2, the two other Cameroonian sites. This quite surpris- orchid fl ora of the Mbam Minkom Hills is one of ing richness and the important number of new the richest of Central Africa (Fig. 6; Table 3). taxa (8%) found in the Mbam Minkom Hills can Other sites that are above the curve are Bali be explained by the method used in this study. Nguemba forest reserve, Príncipe Island, Mount Contrary to other studies that only relied upon Cameroon area, Mount Kupe area, Gabon and collection of fl owering plants in the fi eld, our Cameroon. Moreover, it is very likely that the study used the shadehouse method, which has specifi c richness of this area is still underesti- successfully been applied by different authors to mated as several plants in culture have not fl ow- ORCHIDS OF THE MBAM MINKOM HILLS (CAMEROON) 119

Fig. 4. Distribution of orchid ﬂ ora of the Mbam Minkom Hills (GCR = Guineo Congolian wide; Wide = widespread, Linking = Regional linking species, GCR = Guineo Congolian wide, GCR sub end = Guineo Congolian subendemic, GCR-LGC = Guineo Congolian – Congolian/Lower Guinea linking species, GCR-LG= Guineo Con- golian endemic to Lower Guinea, GCR-LGUG = Guineo Congolian linking species – Upper Guinea/Lower Guinea). The phytogeographical status is supplied by Kew Monocot Checklist (GOVAERTS et al. 2007) using White’s chorological classiﬁ cation (WHITE 1979, 1983).

study orchid diversity in tropical Africa (SAN- restricted species (76%). However, in the Mbam FORD 1969, 1971, PEREZ-VERA 2003, STÉVART Minkom Hills, most inselbergs are surrounded by 2003, DROISSART et al. 2006, DROISSART 2009). submontane forests. Inselbergs usually shelter the epiphytic fl ora of the surrounding vegetation ECOLOGY AND DISTRIBUTION (STÉVART 2003). Therefore, we should consider Most orchids from the Mbam Minkom Hills are widespread species or Guineo-Congolian species. Of these Guineo-Congolian species, 19% are endemic to the Lower Guinea Domain. This fi g- ure differs strongly from the Gamba Complex in South Gabon where STÉVART & DROISSART (2006) found only 7% of Lower Guinea endemics for a similar number of species. The Gamba complex is situated at a low elevation, more to the South and is close to the sea. It is covered mainly by lowland forest, savannah and swampy vegetation. More- over, the inselbergs and the submontane forests of the Mbam Minkom Hills possess seven of the 14 species endemic to Lower Guinea Domain. These habitats are less frequent in the Gamba complex, Fig. 5. Number of taxa according to conservation status even if the area is much larger. using IUCN Red List Categories (number of taxa and The highest specifi c richness in the Mbam percentage of the total orchid fl ora). Conservation Minkom Hills was encountered in lowland forests categories used in this paper come from existing publi- (51 taxa). This habitat also harbours most cations (CRIBB et al. 2000, CRIBB & POLLARD 2004, POLLARD et al. 2004, DROISSART et al. 2006). 120 BELGIAN JOURNAL OF BOTANY 142

Fig. 6. Relation between log speciﬁ c richness (number of taxa) and log area expressed in km in 15 countries and sites. Values for area and species richness are summarized in Table 3.

Table 3. Area (km2), speciﬁ c richness (SR), and orchid species density (species/km2) of 15 countries and sites in West Central Africa. Data from STÉVART (2003), Kew checklists (CRIBB 1998, CRIBB et al. 2000, CRIBB & POLLARD 2004, POLLARD et al. 2004) and SIMO (2003).

Countries/Sites Area (km2) SR Density (species/km2) Bali Nguemba Forest Reserve 8 85 10.6250 Annobon 17 19 1.1176 Mbam Minkom Hills 100 75 0.7500 Principe 136 71 0.5221 Banyang Mbo Wildlife Sanctuary 665 93 0.1398 Sao Tomé 854 104 0.1218 Mount Oku 1550 85 0.0548 Bioko 2000 98 0.0490 Mount Kupe 2390 183 0.0766 Mount Cameroon 2700 150 0.0556 Cristal Mountains 4100 126 0.0307 Dja Fauna Reserve 5260 111 0.0211 Rio Muni 26000 182 0.0070 Gabon 257700 400 0.0016 Cameroon 475000 489 0.0010 the fl ora of both habitats as a unique fl ora that indeed very variable between species, from a few possesses 36 taxa, 66% of which are restricted to days to more than one month. Maximal fl owering those habitats. periods for the species of our study site are One of the functions of the shadehouse is to observed from March to May and from July to study long-term orchid phenology in order to September. The peak fl owering periods corre- complete fi eld observations, especially for species spond to the small rainy season, the small dry sea- with fugacious fl owers. The fl owering duration is son and the beginning of the long rainy season. ORCHIDS OF THE MBAM MINKOM HILLS (CAMEROON) 121

CONSERVATION site (SONKÉ et al. 2006). The study site, despite its proximity to Yaoundé, also harbours two emblem- Major threats for orchid populations are habi- atic and highly threatened animal species: the tat destruction and overcollection (HEYWOOD & gorilla and the grey-necked picathartes. However, STUART 1992, WHITMORE & SAYER 1992). In the the area is under important anthropic pressure and Mbam Minkom Hills, orchids are threatened by primary forest and its associated biodiversity loss and fragmentation of their habitat. According might well disappear in a near future in the to BULAFU et al. (2007), the most important and absence of an active conservation strategy. vulnerable habitats are moist forest habitats. Although the exact relationship between habitat destruction and orchid species extinction is not CONCLUSION known (HEYWOOD & STUART 1992, WHITMORE & SAYER 1992), it has been shown that epiphytes are The orchid fl ora of Cameroon is far from being vulnerable to extinction through habitat destruction completely known, as shown by the six new taxa (TURNER et al. 1994). Most orchids are light-de- and the new national record found during this study. manding epiphytes that grow on the upper part of The orchid fl ora of the Mbam Minkom Hills is one the canopy of largest and oldest trees. Local human of the richest of Central Africa. Moreover, knowl- populations of the Mbam Minkom Hills are very edge of the fl ora will increase since some living scarce, but are dependent on forest resources to plants collected in that remain to be identifi ed meet their basic needs. As a consequence, the because they have not fl owered yet. New sampling recent increase of local human population in the efforts using climbing material should be made in Mbam Minkom Hills has an obvious ecological the area to complete our preliminary work. Although impact on the forest ecosystem. These activities the diversity of its fl ora and fauna has been high- include agriculture, logging and hunting. Forest lighted, a conservation plan is still needed. Ex situ habitat in the Mbam Minkom Hills is believed to orchid conservation in the Yaoundé shadehouse is be threatened with clearance for agriculture. Farm- possible, but an in situ conservation strategy would ers are involved in the destruction of a considerable be preferable considering the submontane ecology portion of the lowland forests for the establishment of most threatened species and the diffi culty to of cocoa and plantain plantations. Timber exploita- maintain these species in culture in Yaoundé. tion by private owners is also an important eco- nomic activity, especially during the dry season. Trees are logged every year, particularly Triplochi- ACKNOWLEDGEMENTS ton scleroxylon K. Schum., which harbours many orchid species situated at the base and in the middle We would like to thank the National Herbarium of parts of the canopy (JOHANSSON 1974). Cameroon staff for allowing access to the herbarium Another conservation problem for orchids collection, and late Dr. Dzikouk, Program Offi cer of lies in their dependence on particular species of Cameroon Biodiversity Conservation Society for logis- pollinators for their reproduction. If the habitat tic help and accommodation offered during fi eldwork becomes too small or fragmented to support the activities. Fieldwork in Cameroon was funded by the pollinator, the orchid species will not regenerate Communauté Française de Belgique, the Fonds David and eventually die out (HEYWOOD & STUART et Alice Van Buuren and the Fonds Leopold III pour 1992), even though there may be enough habitat l’Exploration et la Conservation de la Nature. We are left for the plants to grow in. also grateful to the Royal Belgian Institute of Natural Sciences and the Belgian National Point to the Global The Mbam Minkom Hills are a site of con- Taxonomy Initiative for fi nancial support offered in cern for orchid conservation in Cameroon because 2007 to the fi rst author. The authors thank Dr. Barbier it harbours some of the rarest or most endangered for helpful comments and suggestions, Mrs. Justine orchids of the Lower Guinea endemism area. Kemlo for checking the English and Prof. Lejoly for Even some Rubiaceae are known only from this facilities offered in his laboratory. 122 BELGIAN JOURNAL OF BOTANY 142

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