Roepera Genus

Roepera is a genus of flowering plants in the family Zygophyllaceae, placed in subfamily Zygophylloideae and the order Zygophyllales. The genus comprises approximately 60 species of shrubs, subshrubs, and herbaceous plants, primarily distributed across warm and arid regions of Australia and southern Africa.

Vegetatively, species of Roepera are recognisable by their opposite leaves, which may be stalked or sessile and bear one or two leaflets. Shrubby members can reach up to 3 metres in height. The flowers have four or five sepals — which persist into the fruiting stage — and four or five petals of varied colours. The eight to ten stamens typically bear undivided appendages, and the ovary is divided into four or five chambers. The fruit is most commonly a capsule; in some species it is a winged schizocarp. Seeds are mucilaginous and possess a more-or-less developed aril.

The genus has a notable taxonomic history. It was first described by Adrien-Henri de Jussieu in 1825 for two Australian species then placed in Zygophyllum, though the formal new combinations were not published until George Don did so in 1831. For most of the following two centuries Roepera remained largely unused, with its species retained in the broader Zygophyllum. Molecular phylogenetic studies in 2000 and 2003 demonstrated that Zygophyllum, as then circumscribed, was polyphyletic. In 2003, Beier and colleagues resurrected Roepera and transferred approximately 60 Zygophyllum species into it, rendering Zygophyllum monophyletic. Plants of the World Online recognised 60 species as of January 2018.

The genus has a disjunct distribution, native to Australia on one side and to the western coast of southern Africa — Angola, Botswana, Namibia, and the Cape Provinces and Free State of South Africa — on the other. Biogeographic analyses suggest the genus originated in Africa and dispersed to Australia roughly 12 million years ago.