Floristic Diversity of African and South American Inselbergs: a Comparative View

Porembski Stefan

Universität Rostock, Institut für Biodiversitätsforschung, Allgemeine und Spezielle Botanik, Rostock, Germany

Inselbergs consist of Precambrian rocks and form ancient (often > 50 million years), stable landscape elements that are widespread on old crystalline shields. Characterized by harsh environmental conditions, their vegetation is clearly different from that of the surroundings. This gives inselbergs island-like attributes, and being geologically uniform they bear a vegetation whose composition and diversity is determined by the regional climate, vegetation history and local establishment/extinction dynamics.

On both tropical and temperate inselbergs, a typical set of physiognomically defined habitats (e.g. ephemeral flush vegetation, monocotyledonous mats, rock pools, shallow depressions) occurs.

Globally c. 3500 angiosperm species grow on inselbergs. Certain families are characterized by a particularly high percentage of inselberg specialists, e.g. Velloziaceae (c. 24% of all species on inselbergs), Lentibulariaceae (c. 16%) and Xyridaceae (11%). Floristically there are large differences in species richness and the number of endemics between separate regions, but there is no clear trend of increasing diversity from temperate regions towards the tropics. On African inselbergs Fabaceae, Scrophulariaceae and Lentibulariaceae belong to the most species-rich families whereas Melastomataceae, Orchidaceae, Bromeliaceae and Euphorbiaceae are dominant on South American inselbergs.

With regard to the species richness of individual habitats the ephemeral flush vegetation is top ranking on African inselbergs in contrast to South American inselbergs where monocotyledonous mats form the most species-rich habitat. According to preliminary data, inselberg-specific taxa in Africa possess larger distributional areas than in South America.