Discovery of a new exotic cactus, Opuntia megapotamica Arechav. (Cactaceae) in South Africa using molecular data.

Abstract

Abstract Some of the most dominant and widespread invasive species in South Africa are in the Cactaceae. The genus Opuntia contains almost half of the invasive cacti including the taxonomically challenging O. engelmannii Salm-Dyck ex. Engelm from North America. Three morphologically distinct varieties, O. engelmannii Limpopo, O. engelmannii Northern Cape and O. engelmannii Eastern Cape, were considered to be present in South Africa until recently. Confirming the identity of invasive O. engelmannii varieties is crucial for biological control using species-specific cochineals. To determine the identity of the varieties we inferred the phylogenetic relationships among them using sequence data of the intergenic trnL-F chloroplast region with representatives of morphologically similar cactus species from both North and South America obtained from GenBank. The cpDNA sequence dataset resulted in 429 characters containing seven parsimonious base pairs. Our phylogenetic analysis indicated that the Eastern Cape variety of O. engelmannii was closely matched with the South American Opuntias, with an identical cpDNA sequence matching O. megapotamica Arechav, while the other members of the O. engelmannii species complex, including the Limpopo and Northern Cape varieties, formed a monophyletic clade of the North American Opuntias. Our study confirms the presence of this cactus species outside its native range, which was previously misidentified in South Africa. More importantly, our study shows that exploration for potential cochineal biocontrol agents of the invasive O. megapotamica should be conducted in South America rather than North America, where previous potential biological control agents have been imported from.