Achene heteromorphism in the cleistogamous species Centaurea melitensis

Centaurea melitensis is a cleistogamous annual plant displaying achene hete romorphism. Variation is linked to capitulum type: a) initial cleistogamous capitula produce thick achenes bearing a shea pappus; b) in final cleistog amous capitula achenes are small with a short pappus; and c) chasmogamous c apitula produce small achenes with a longer pappus. The present study, carr ied out in Cordoba (Spain), examines variability in achenes by analysis of morphology, timing, dispersal and germinative capacity, and monitors the su bsequent development of seedlings at different densities. Results confirm t he heterogeneous nature of the achenes produced, and suggest that Centaurea melitensis has developed a life history strategy (cleistogamy and achene h eteromorphism) highly adapted to the unstable habitat (subnitrophilous pion eer pasture communities) in which it grows. (C) 2000 Editions scientifiques et medicales Elsevier SAS.