BackgroundSouth African plant species of the genera Fadogia, Pavetta and Vangueria (all belonging to Rubiaceae) are known to cause gousiekte (literally ‘quick disease’), a fatal cardiotoxicosis of ruminants characterised by acute heart failure four to eight weeks after ingestion. Noteworthy is that all these plants harbour endophytes in their leaves: nodulating bacteria in specialized nodules in Pavetta and non-nodulating bacteria in the intercellular spaces between mesophyll cells in Fadogia and Vangueria.Principal FindingsIsolation and analyses of these endophytes reveal the presence of Burkholderia bacteria in all the plant species implicated in gousiekte. Although the nodulating and non-nodulating bacteria belong to the same genus, they are phylogenetically not closely related and even fall in different bacterial clades. Pavetta harborii and Pavetta schumanniana have their own specific endophyte – Candidatus Burkholderia harborii and Candidatus Burkholderia schumanniana – while the non-nodulating bacteria found in the other gousiekte-inducing plants show high similarity to Burkholderia caledonica. In this group, the bacteria are host specific at population level. Investigation of gousiekte-inducing plants from other African countries resulted in the discovery of the same endophytes. Several other plants of the genera Afrocanthium, Canthium, Keetia, Psydrax, Pygmaeothamnus and Pyrostria were tested and were found to lack bacterial endophytes.ConclusionsThe discovery and identification of Burkholderia bacteria in gousiekte-inducing plants open new perspectives and opportunities for research not only into the cause of this economically important disease, but also into the evolution and functional significance of bacterial endosymbiosis in Rubiaceae. Other South African Rubiaceae that grow in the same area as the gousiekte-inducing plants were found to lack bacterial endophytes which suggests a link between bacteria and gousiekte. The same bacteria are consistently found in gousiekte-inducing plants from different regions indicating that these plants will also be toxic to ruminants in other African countries.

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Acanthopsis is a taxonomically poorly understood genus confined to arid parts of southern Africa. This contribution is the first detailed assessment of the diversity within the Acanthopsis disperma-hoffmannseggiana complex, the latter of which comprises the bulk of the specimens of the genus represented in herbaria. Species concepts are resolved and the misapplication of names is noted. In addition to the recognition of A. disperma and A. hoffmannseggiana, five new species of Acanthopsis formerly treated under these two names, are described, namely A. tuba and A. ludoviciana (both confined to the Richtersveld, Northern Cape, South Africa), A. adamanticola (endemic to southern Namibia), A. villosa (endemic to Bushmanland, Northern Cape) and A. dispermoides (endemic to the Western Cape, South Africa). The names A. disperma and A. hoffmannseggiana are lectotypified here. An identification key to the members of the Acanthopsis disperma-hoffmannseggiana complex is provided, as well as an interim key to the major artificial groupings in the genus, the taxonomy of some which still needs to be resolved.

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