A taxonomic revision of Cenchrus L. (Poaceae) in Thailand, with lectotypification of Pennisetummacrostachyum 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. Pennisetummacrostachyum , a synonym of Cenchruspurpureus 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.