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Polhilia – revision of lesser known Cape plant genus ensures conservation
Author: Wiida Fourie-Basson
Published: 09/02/2021

​One of the Cape Floral Kingdom's most threatened plant genera, Polhilia, has now been comprehensively revised and populations of these endangered species documented, thereby aiding efforts to ensure its conservation.

This is thanks to the field work and research completed by Brian du Preez, a keen botanist and PhD student, for his MSc studies in the Department of Botany and Zoology at Stellenbosch University (SU). The result of his work was recently published as a monograph of the genus Polhilia in the South African Journal of Botany. In this study, four new species are described, bringing the total number of species in this genus to 11, all of which are threatened with extinction, and classified as critically endangered.

Polhilia species grow in Renosterveld, a vegetation type endemic to the Cape. But more than 90% of Renosterveld has been severely transformed for crop agriculture, resulting in Polhilia species, along with countless other threatened plants, being confined to small patches of remaining Renosterveld," he explains.

Brian set out to revise the taxonomy of this lesser-known plant genus after he accidentally rediscovered 13 bushes of the long-lost species Polhilia ignota growing on the farm Goede Hoop near Eendekuil in 2016. Until this discovery, this species was known from only two collections made in 1924 and 1928 in the Porterville and Saldanha areas respectively, and thus listed as extinct on SANBI's Red List of South African Plants. In 2017 he discovered a single plant of Polhilia ignota growing along a fence next to the N7 highway only five kilometers north of Piketberg. Subsequently, members of the Custodians of Rare and Endangered Wildflowers (CREW) found another two populations nearby Voëlvlei Nature Reserve and southwest of Porterville, bringing the total number of known plants to roughly 230.

Brian says he covered nearly 8 000 kilometers by road, and nearly a hundred by foot, searching for more populations of Polhilia growing in the small patches of remaining Renosterveld in the Overberg and Swartland, including two field trips to the Roggeveld escarpment near Sutherland. One of the high lights of his many field trips was the discovery of a new species, Polhilia fortunata, near Vanwyksdorp in the Little Karoo.

While passionate about his fieldwork, Brian says he felt overwhelmed when confronted with the degradation and destruction of the original Renosterveld: “One can only try to imagine what the area used to look like before the first ploughs moved in. Back then there were no environmental laws regarding protected species or their habitats."

Prof Léanne Dreyer, a botanist at SU and one of Brian's study leaders, says the taxonomic revision of these endangered species are extremely important: “If we don't know about these species and their populations, then we cannot conserve them. Based on Brian's work, herbariums the world over will now revise and update their collections based on the latest information. He also established the conservation status of each of the 11 species, which is critically important for their future."

Brian is currently working with the curator of the Stellenbosch University Botanical Gardens, Dr Donovan Kirkwood, to establish al 11 species of Polhilia in its collection. This means that plant material can be shared with other botanical gardens in the world, another insurance policy to ensure the future survival of these species. In the case of one of the newly discovered species, Polhilia groenewaldii, for example, there are only four plants left in the wild.

On the photo above: The newly discovered Polhilia groenewaldii honours Mr Jannie Groenewald, former plant specialist at Haarwegskloof Nature Reserve, who first discovered it near Bonnievale. There are currently only four of these plants known to have survived in the wild. Photo: Brian du Preez

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