The Namib-Thar Desert Disjunction in Dactyliandra (Cucurbitaceae) is the Result of a Recent Introduction to India

Depending on taxonomic concept, the genus Dactyliandra (Cucurbitaceae) comprises up to four species: two from Southwest Africa, D. luederitziana (Namibia) and D. welwitschii (Angola), and two very locally distributed and poorly known taxa from Northeast Africa, D. nigrescens and D. stefaninii. In addition to these African populations, D. welwitschii was also reported as a possibly native species from the Thar desert of Northwestern India and Pakistan ca. 8,000 km away from the Namib range. A phylogenetic analysis of plastid and nuclear ribosomal ITS DNA sequences including all Dactyliandra species and D. welwitschii from the Thar desert revealed that this striking disjunction is of very recent origin. Dactyliandra is monophyletic only after exclusion of the East African taxa, which are best placed in Trochomeria. The species Dactyliandra welwitschii is monophyletic and includes the Indian plants, which group with a sample from an Angolan population. We hypothesize that this unexpected connection is a result of man-mediated introduction to India from Africa perhaps in the times of the slave trade. The new combinations Blastania lucorum and Trochomeria nigrescens are published here.