Pollia

Abstract: Africa (including Madagascar) has nearly twice as many species of Commelinaceae as any other continent (approximately 270 species, or about 40% of the total in the family). Of the 17 genera which are native, seven ( Anthericopsis, Coleotrype, Palisota, Polyspatha, Pseudoparis, Stanfieldiella and Triceratella ) are endemic, the highest percentage generic endemism of any continent. Within Africa gcneric diversity is slightly higher in western than in eastern tropical floras. Species richness, however, is greatest in eastern Africa, mainly due to a high diversity of species of Commelina and Aneilema. Africa shares more genera with Asia (nine) than with any other continent. Only one African genus, Buforrestia, is neither endemic nor shared with Asia. Its western African/northeastern South American distribution is unique in the family. Besides Buforrestia , only five other genera of Commelinaceae (out of a total of 50 in the family), occur in both the Old and New Worlds. These genera. Aneilema, Commelina, Floscopa, Murdannia and Pollia are all very widespread in the Old World, occurring in Australia and Asia in addition to Africa (both continental and Madagascar). Madagascar is relatively poor in species (31). but these include the endemic Madagascan genus Pseudoparis , the sole African species of Rhopalephora , and the largest number of species of the Afro-Malagasy endemic genus Coleotrype . The high rate of generic endemism of Commelinaceae in Africa probably indicates that Africa was one of the ancient centres of diversity for the family. The high species diversity is more likely due to relatively recent radiations by genera pre-adapted to survival in non-forest habitats. The occurrence of only a small number of genera on both sides of the Atlantic suggests that the Commelinaceae have been evolving independently in the eastern and western hemispheres for a long period.