Tithonia diversifolia (Mexican sunflower) in south-western Nigeria: occurrence and growth habit

A reconnaissance survey of the occurrence of Tithonia diversifolia (Hemsl.) A. Gray in southwestern Nigeria was carried out along the major highways linking Ibadan to major towns between April and August in 1991 and 1992. The survey revealed that T. diversifolia is prominent along the Ibadan-Oyo-Ogbomosho-Ilorin, Ibadan-Abeokuta and Oyo-Iseyin-Saki roads, and common along the Ibadan-Iwo-Osogbo-Offa, Ibadan-Ife-Akure, Ife-Ondo and Ibadan-Ijebu Ode roads. It is rare along Ibadan-Ikeja, Akure-Ado Ekiti-Kabba, Ilorin-Jebba, and Ijebu Ode-Benin City-Asaba roads. T. diversifolia is a shallow-rooted annual/perennial broad-leaved plant that grows to a height of 5 m or more and varies from highly branched at low populations (<5 plants m(-2)) to practically unbranched at high populations (>30 plants m(-2)). Under natural conditions in the Ibadan area (7 degrees 25'N, 3 degrees 54'E), T. diversifolia is established from seed in March-April, flowers between September and November and produces mature seed by December-January. Seed is disseminated between January and March by shedding. Under frequent slashing or in a valley bottom with a high water table, or on river banks T. diversifolia behaves as a perennial shrub and flowering under this condition occurs sporadically throughout the year.