A taxonomic revision of Socotran Indigofereae (Leguminosae - Papilionoideae) with insights into the phytogeographical links of the Socotran archipelago

This revision of Socotran Indigofereae (Leguminosae) treats two genera, Microcharis and Indigofera, and 16 species, one with two varieties. Indigofera coerulea var. coerulea and I. nugalensis are new records for the archipelago. Indigofera nephrocarpoides, I. marmorata (lectotypified here) and I. socotrana are endemic, whilst Microcharis disjuncta var. fallax and Indigofera nugalensis are near-endemic to the Socotran islands. This study indicates that the closest relatives of the Socotran Indigofereae are to be found in African lineages. The strongest affinities are between Socotra and extreme NE Somalia (Indigofera pseudointricata, I. nugalensis) and, to a lesser extent, with SW Oman (Microcharis disjuncta var. fallax), SW Pakistan (I. nephrocarpa) and Southern Yemen. Socotran Indigofereae are mainly derived from Tertiary African palaeotropical and drought-adapted lineages. We also suggest that following the separation of the islands from mainland Africa some Indigofereae would have reached the archipelago as a result of recent, long-distance dispersal events.