Endemic plants of the arid succulent karoo in Namibia: towards hypotheses for their evolution

Authors

  • Antje Burke


A. Burke (antje.burke@enviro-science.info), EnviroScience, P.O. Box 90230, Klein Windhoek, Namibia.

Abstract

This study investigated endemic plants in the Sperrgebiet in the succulent karoo – a global biodiversity hotspot in southern Africa. In order to develop hypotheses regarding the evolution of this endemic flora, the following questions were posed: 1) Are taxonomic patterns similar at different levels of taxonomic order? 2) Are adaptations of Sperrgebiet endemic taxa different from the overall flora? 3) Are adaptations different in related endemic and non-endemic taxa?

There is an over-representation of species of Mesembryanthemaceae in the endemic flora, which is in accordance with patterns in the succulent karoo biome overall. The nearly 37% contribution of Mesembryanthemaceae to the endemic flora is, however, remarkably higher than elsewhere in the biome. The over-representation of this family is not maintained at a higher level of taxonomic order, supporting the notion of recent speciation in this family. Regarding plant functional attributes, major differences between the endemic and non-endemic flora exist. Compact leaf-succulents with canopy stored, water-dispersed seeds, as well as bulbs and shrubby leaf-succulents predominate the endemic flora. Differences in reproductive (seed storage and dispersal distance) and growth form attributes between the endemic and non-endemic flora were largely influenced by phylogenetic history. Minutism (plant height <10 cm) was favoured by many endemic plants, but this was not only influenced by phylogenetic factors.

Two hypotheses emerged from these observations: 1) the evolution of minutism is largely driven by external factors in the Sperrgebiet, and 2) external factors and phylogenetic history are likely of equal importance in the development of the Sperrgebiet endemic flora.

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