Abstract
The genus Sopubia belongs to the family Orobanchaceae (Broomrapes) of the order Lamiales, which comprises almost entirely of parasitic plants except for three (Lindenbergia, Rehmannia and Triaenophora) of its 90 genera. Plants of the family are root parasites; they parasitize on plants like maize, sunflowers, millet and grasses with the aid of haustoria. Sopubia includes about 40 species distributed mainly in distinct areas, the first comprising all tropical Africa (including South Africa), the second stretching from India to southeast Asia and south of Australia. In southern Africa, the genus has never been taxonomically revised since the last revision by Bentham (1800’s), as a result it has been listed by the South African National Biodiversity Institute as one of the priority genera in need of a revision. The study therefore aims to undertake a taxonomic revision of the southern African species of the genus. The objectives of the study are to investigate the vegetative and reproductive characters of diagnostic importance in distinguishing the species of Sopubia, provide a preliminary evaluation of the conservation statuses of the four species in southern Africa and construct a phylogenetic tree based on DNA sequencing of the species of Sopubia and selected outgroups species using ITS and trnT-L gene regions. Despite the medium size of Sopubia in South Africa, it is represented in the region by only four species, namely, S. cana, S. mannii, S. simplex, and S. karaguensis. This study presents morphological characters of diagnostic importance based on observations made on herbarium specimens. The study revealed that species of Sopubia can be morphologically distinguished based on the leaf arrangement, indumentum, leaf type, flower colour and the shape of the capsule. For example, S. cana differs from the other three southern African species in having silvery velvety leaves. However, the leaves are linear like in S. mannii and S. simplex. S. karaguensis has opposite and fleshy leaves. The inflorescence is a spike comparable to other three species, which are S. cana, S. mannii and S. simplex, they have a raceme inflorescence. Sopubia simplex has spheroidal oblong capsule and S. mannii is distinguished by its short and oblong capsule. The flowers in S. karaguensis and S. mannii are purple and in S. cana and S. simplex they are pink. Although the conservation status of the four
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species is recorded as Least Concern in South Africa, the species have a widespread distribution. Field trips were undertaken to KwaZulu- Natal, Limpopo, and Gauteng in search of fresh plant material, unfortunately plants could not be located in the wild. This suggests that the classification might require re-evaluation based on the outcome of the field trips. Phylogenetically Sopubia was strongly supported as monophyletic.
Keywords: Orobanchaceae, Sopubia, taxonomic revision, phylogenetic relationships, conservation status.