A conservation and floristic assessment of poorly known species rich quartz–silcrete outcrops within Rûens Shale Renosterveld (Overberg, Western Cape), with taxonomic descriptions of five new species

Abstract

Quartz fields are islands of distinct vegetation in southern Africa. Such habitats differ from surrounding shale substrate in geomorphological and climatic attributes, and are dominated by a predominantly succulent flora with between 14% and 91% endemism. Previous studies have identified and surveyed quartz fields within the Succulent Karoo biome, but little is known about the Overberg quartz–silcrete fields located in the Renosterveld vegetation (Fynbos biome). This study maps the occurrence of quartz–silcrete fields in the Overberg (Eastern and Central Rûens Shale Renosterveld) and investigates if such fields support distinct vegetation compared with surrounding shales. Forty-seven plant species were recorded, 19 of which are endemic to the quartz–silcrete patches, including several newly discovered species in vascular plant families Cyperaceae (Ficinia), Iridaceae (Hesperantha) and Fabaceae (Aspalathus, Otholobium, Polhillia, Xiphotheca). Five species among these are described in this paper: Aspalathus quartzicola C.H.Stirt. & Muasya, Aspalathus microlithica C.H.Stirt. & Muasya, Ficinia overbergensis Muasya & C.H.Stirt., Otholobium curtisiae C.H.Stirt. & Muasya, and Polhillia curtisiae C.H.Stirt. & Muasya. Detailed floristic composition of 25 quartz fields is surveyed, together with their conservation status. The Overberg Quartzveld is a critically endangered vegetation type that is the sole locality for 18 Red Listed plant species; which include seven new taxa. It is a distinct vegetation unit embedded within Rûens Shale Renosterveld in the eastern Overberg region of South Africa. These quartz patches have been overlooked in the past and we emphasize the need for further research and conservation attention of these habitats.