J. M. Lock 
Flora of Tropical East Africa – Xyridaceae (1999) [PDF ebook] 

The flora is prepared at Royal Botanic Gardens, Kew, in close collaboration with East African Herbarium and in liaison with the University of Dar es Salaam, the University of Nairobi and the Makerere University. Significant contributions are also made by specialists elsewhere. The flora is designed to a high academic standard and should be a useful resource reference for anyone concerned with the identification and utilization of plants in eastern Africa. Each family is published as a separate part.