A taxonomic revision of Cenchrus L. (Poaceae) in Thailand, with lectotypification of Pennisetum macrostachyum Benth

A revision of the genus Cenchrus (Poaceae) in Thailand is reported. Seven species, i.e. C. brownii , C. ciliaris , C. clandestinus , C. echinatus , C. pedicellatus , C. purpureus and C. setosus are described in this taxonomic treatment. This genus is an exotic species and distributed throughout the floristic regions. All the species have become naturalised to Thailand as a weed and found growing in wastelands, open areas by the roadside, disturbed sites, the edge of rice fields and the edge of deciduous and evergreen forests at elevations between 0 and 2,650 m alt. Pennisetum macrostachyum , a synonym of Cenchrus purpureus is lectotypified. Detailed morphological descriptions, illustrations and a key to the species are presented, along with information on distributions, habitats, ecology, phenology, vernacular names and specimens examined.