The extraordinary botanical diversity of inselbergs in Madagascar

Abstract

Rabarimanarivo, M.N., B. Ramandimbisoa, N.H. Rakotoarivelo, P.B. Phillipson, S. Andriambololonera, M.W. Callmander & S. Porembski (2019). The extraordinary botanical diversity of inselbergs in Madagascar. Candollea 74: 65–83. In English, English and French abstracts. DOI: http://dx.doi.org/10.15553/c2019v741a8Inselbergs are isolated mountains, mainly granitic or gneissic rock outcrops rising abruptly above surrounding plains. Malagasy inselbergs are often dome-shaped and occur in varying degrees of isolation, but they sometimes form inselberg landscapes, which comprise dozens of individual outcrops. Despite being typical landscape features on Madagascar's high plateau, little data are available on their detailed plant cover. Recent extensive fieldwork, which was conducted between 2010 and 2014, mainly on the central plateau, has resulted in a better knowledge about the floristic composition and habitats of Malagasy inselbergs. The most speciose vascular plant genera were Cynorkis Thouars (18), Cyperus L. (15) and Euphorbia L. (14). Malagasy inselbergs are centres of diversity for succulents (notably species of the genera Aloe L., Euphorbia and Kalanchoe Adans.), carnivorous plants (species of Drosera L. and Utricularia L.) and resurrection plants (notably species of Xerophyta Juss.). The most speciose habitat types were ephemeral flush vegetation and monocotyledonous mats. The latter habitat supports a large number of succulents and resurrection plants. In total 724 taxa out of 338 genera and 107 families have been recorded. Moreover, the variability in floristic composition between different regions is remarkable. Detrimental human impacts include quarrying, grazing, fire and the collection of plants for ornamental purposes (species of Pachypodium Lindl. and Orchidaceae) and as medicine (species of Aloe, Drosera madagascariensis DC., Myrothamnus moschatus (Baill.) Baill.). For the first time, recommendations are made for the conservation of Malagasy inselbergs.