Phytogeography of Passerina (Thymelaeaceae)

Abstract

Passerina L. comprises 20 species and four subspecies of microphyllous. wind-pollinated shrubs. Once considered cos­mopolitan, the genus as currently defined, is endemic to southern Africa. Endemism within the genus is highest in the Cape Floristic Region (CFR), where all members show morphological and anatomical adaptations to the winter rainfall and dry warm summers of the Mediterranean or semi-Mediterranean climate of the region. The Western Cape is the centre of diversity for Passerina, from where certain species extend to the west, north and east. The outlier populations of Passerina montana Thoday on the interior plateau of South Africa and Zimbabwe, as well as the Auas Moutains in Namibia, most probably origi­nated in the CFR and formed part of a previously wider northern temperate Afromontane grassland-dominated vegetation during the Quartemary, of which relicts remained in the high mountain areas. P. burchellii Thoday and P. paludosa Thoday have the most restricted distribution and are regarded as Vulnerable. All other species are either widespread or under no im­mediate threat.