Selbyana 26(1,2): 125-133, 2005. DISTRIBUTION, ECOLOGY, AND THREAT TO SELECTED MADAGASCAN ORCHIDS PHILLIP CRIBB, * DAVID ROBERTS, AND JORAN HERMANS Herbarium, Royal Botanic Gardens, Kew, Richmond, Surrey, Great Britain, UK. Email: [email protected] ABSTRACT. Madagascar has a rich orchid flora, approaching 1000 species, of which almost 90% are considered to be endemic. Published information on the orchids includes only generalized information on distribution aud ecology aud nothing on their conservation status in the wild or threat of extinction. Nev­ ertheless, it is widely considered that mauy Madagascau orchids are threatened, particularly by habitat destruction that has been widely reported. Little factual data, however, has been published on these aspects of Madagascan orchids. Using herbarium data, we have entered the known historical distribution of species from different habitats in Madagascar onto base maps that include details of geology, elevation, aspect, aud vegetation type. These maps can be used to indicate where species occurred historically and whether the vegetation they once occupied still persists. They also cau be used to indicate where a species might be found in surviving stauds of natural vegetation. Herbarium records based on algorithms developed to predict possible extinction events cau be used to prioritize the rare taxa most under threat. These predictive algorithms have been applied to a selection of Madagascau species that are considered to be threatened by extinction. Key words: Orchidaceae, extinction, algorithm, distribution, herbaria INTRODUCTION inselberg and sandstone massifs of the central plateau region. Madagascar has a rich orchid flora, approach­ Ex-situ propagation of selected species also is ing 1000 species in 59 genera. Of these more being undertaken as part of the program for ex­ than 88% of the species and 17.6% of the genera hibition at Parc Tsimbazaza and to provide the are considered to be endemic (TABLE 1). The last horticultural trade with healthy seedlings and floristic account appeared some 62 years ago take the pressure off the remaining populations. (Perrier de la BiHhie 1939-1941), and an updat­ Madagascar is a large island, about two and ed checklist was published recently (Du Puy et a half times the size of Great Britain and with a al. 1999). These treatments included only gen­ population of about 16 million people. Estimates eralized information on distribution and ecology, of vegetation cover provided by Dufils (2003) and nothing on the conservation status of plant suggest that about 5.5 million ha of evergreen species in the wild or the threat of extinction forest survive, mainly in the mountains on the facing them. It is widely considered, neverthe­ eastern side of the island along with some in the less, that many Madagascan orchids are threat­ north. Dry forest is the second largest area of ened, particularly by habitat destruction that has natural habitat with 4.1 million ha surviving been widely reported. (FIGURE O. Secondary vegetation covers 7.1 Little factual data, however, has been pub­ million ha and mangrove forest, 435,000 ha. Or­ lished on these aspects of Madagascan orchids. chids occur in all these habitats. Another signif­ Using herbarium-based data, we have entered icant orchid habitat is provided by the granite past and present distributions onto base maps sandstone on the central plateau region and the that show remaining vegetation classified as to limestone outcrops in the north and west of the type and extinction modelling. These base maps island. indicate that some species indeed are endan­ Du Puy and Moat (1996) provided a base map gered and that many survive in healthy numbers of existing natural vegetation type using satellite in remaining habitats. Currently team members imagery and geological and edaphic data. Some of a collaborative project sponsored by Kew, distinct vegetation types, often greatly reduced Parc Tsimbazaza, and the University of Anta­ from their former extents, are not included in nanarivo are undertaking studies of the ecology, any of the current national parks. population size and structure, and pollination success of a number of threatened orchids from ORCHID HABITATS the eastern rain forests and from both granite AND TAXONOMIC TREATMENTS Some of the major orchid habitats in Mada­ * Corresponding author. gascar (eastern rain forests, inselbergs and sand- 125 126 SELBYANA Volume 26(1,2) 2005 TABLE 1. Endemism in Madagascan orchids. stone outcrops on the plateau, dry forests, sec­ ondary grasslands, marshes and rice paddy) are Species Endemic Endemism described below, along with a selection of char­ Genus No. species No. % acteristic orchid species. Acampe 1 a a Aerangis 20 15 75 Aeranthes 41 39 95 Eastern Rain Forests Agrostophyllum 1 a a This is the most extensive of all the remaining Ambrella* 1 1 100 Angraecopsis 1 a a vegetation zones and extends across the north Angraecum 143 131 92 and down the east of the island inland from the Auxopus 1 1 100 coast to the crests of the mountains that parallel Bathieorchis* 1 1 100 the coast. The rain forest is in better condition Beclardia 2 1 50 in the north and northeast than further south, Benthamia 28 26 93 where extensive clearance has left, at best, a mo­ Brachycorythis 2 1 50 Brownleea 2 a a saic of forest patches and often no forest cover Bulbophyllum 197 187 93 at all. The most extensive area of forests sur­ Calanthe 5 4 80 vives in the Masoala Peninsula in the northeast. Cheirostylis 1 o o Botanical exploration of this region remains lim­ Corymborkis 1 o a ited because of its relative inaccessibility. Cryptopus 3 2 67 Cymbidiella* 3 3 100 Eulophiella roempleriana (Rchb.f.) Schltr. be- Cynorkis 162 153 94 longs to an endemic genus of three species Didymoplexis 1 1 100 (FIGURE 2A). A showy orchid, it is confined Disa 4 3 75 Disperis 21 15 71 to the eastern rain forests of the island from Eulophia 25 18 72 Ranomafana in the south to lIe Ste Marie in Eulophiella* 4 4 100 the north. This epiphyte apparently is con­ Galeola 1 1 100 fined to the crowns of Pandanus. Its host Gastrorchis* 9 9 100 tree is usually P. utilis, up to 25 m or so Goodyera 4 4 100 tall, that grows in forest swamps. Unfortu­ Grammangis* 2 2 100 nately, the orchid is collected from acces­ Graphorkis 3 2 67 Gymnochilus 2 2 100 sible sites for the horticultural trade, result­ Habenaria 27 20 74 ing in some colonies having very few (3- Hetaeria 1 1 100 10) adult plants or no longer having any at Imerinaea* 1 1 100 all. A more severe problem is that the host lumellea 48 47 98 is harvested for its leaves, which are used Lemurella 4 3 75 for weaving baskets. On lIe aux Nattes at Lemurorchis* 1 1 100 Liparis 38 35 92 the south end of lIe Ste Marie, the orchid is Malaxis 4 4 100 protected, but its unprotected host tree is Megalorchis* 1 1 100 regularly harvested. No adult orchids sur­ Microcoelia 10 8 80 vive in the wild there, but seedlings were Microterangis 4 3 75 found in one swamp. Other showy orchids, Neobathiea 6 5 83 such as Cymbidiella falcigera that grows on Nervilia 8 2 25 Oberonia 1 a o raffia palms, were common in the swamps Oeceoclades 24 19 79 nearby, suggesting that the harvesting of the Oeonia 4 2 50 host had a greater effect than collecting the Oeoniella 1 o o orchid. Fortunately, in December 2003, Phaius 1 a a fieldwork at Ranomafana, Mantadia, and Physoceras* 9 9 100 Ambovatikely located several healthy pop­ Platycoryne 1 a a Platylepis 4 2 50 ulations of E. roempleriana in remote pla­ Polystachya 22 18 82 ces with up to 50 mature plants. Observa­ Satyrium 5 3 60 tions of pollinating bees attracted to the Sobennikoffia* 4 4 100 flowers suggest that the orchid flowers Solenangis 2 a a might mimic those of tree Melastomataceae Tylostigma* 7 7 100 that have similar rose-purple flowers with Vanilla 5 5 100 Zeuxine 3 3 100 bright yellow anthers. 59 936 829 88 Eulophiella elisabethae Rolfe is closely allied * Endemic. Of the 59 genera, 12 are endemic. to E. roempleriana but has smaller white Source: Du Puy et al. (1999), La Croix et al. (2002), and pink flowers in shorter denser inflores­ Bosser and Cribb (2003). cences (FIGURE 2B). Like the latter it also SECOND lOCC PROCEEDINGS 127 J• OJI I N " Legend tvergreea F~tiom;! BJ:D COASTAL fUkES1' {Wl'!S'!13RN} @~ :£VEaGJUmN, RUMIDFOREST IJ.fJW ALTI'l'fJDE) _~,HUMlDFOREST(MlDAL'IlTtJD£} _twERGREEN,HtJMIOf'OREST(WWERMONTANSl _ MQNrAN£(PHlUPPIMSCRfJBLANO _~\SCUlROPRYU,OUS(UAPACA)~ l>eclduoIUF01'~ _COA3TALro~(E.ASl'£RN} IToliara _ DECIDUOUS, SEASONALLY MY, WfiS'l'ERN FOREST I ~DECIDUOt)'S, DRY,SOt.rrHERN.FOOEST AND SCRUBLANO o 50 100 150 Kilometres ,, ___ ,____ --'--'-L ___ ,__ , Projection: Geographic FIGURE 1_ Remaining primary vegetation in Madagascar (Du Puy & Moat 1996). 128 SELBYANA Volume 26(1,2) 2005 A B c o E F H G FIGURE 2. Madagascan orchids. A. Eulophiella roempleriana. B. Eulophiella elisabethae. C. Eulophia epi­ phytica. D. Angraecum sesquipedale. E. Aerangis ellisii. F. Angraecum magdaLenae. G. Aeranthes henrici. H. Vanilla madagascariensis. SECOND IOCC PROCEEDINGS 129 favors a specific host, namely a palm, Dyp­ produced when the rains start. Vegetation suit­ sis fibrosa (C.H. Wright) Beentje & Dransf. able for orchids is very limited nowadays in this With a distribution far more restricted than region. In contrast, the rocky outcrops of granite that of E. roempleriana, it has been found and sandstone have their own distinct flora, in­ only on the southern and northern margins cluding orchids. Some Angraecum and Jumellea of the Masoala Peninsula (Dransfield & Be­ species grow on the bare rocks or on grassy tus­ entje 1995).