Cleistogamy in Centaurea melitiensis L. (Asteraceae): Reproductive morphological characters, analysis, and ontogeny

In morphological terms, cleistogamy is the most extreme form of autogamy. A mong other characteristics, cleistogamy generally entails a reduction in fl ower size, one that particularly affects the corolla and androecium. In thi s study, we compare, from a structural point of view, the changes observed in cleistogamous (CL) flower heads of the annual herb Centaurea melitensis to the changes in chasmogamous (CH) heads throughout floral ontogeny. Speci al attention was paid to capitulum structure, since no other reports of cle istogamic differences similar to those observed here for C. melitensis are to be found in the literature ion Asteraceae. Anthesis was absent in both t he CL capitulum itself and in the florets within it. In comparison with CH heads, the fertile florets in CL heads were smaller and less numerous, and sterile florets tended to be lacking, as did several floral structures. Flo ral initiation and development in CH flower heads did not follow the strict ly acropetal pattern typically observed in the rest of the Asteraceae famil y. There is evidence to indicate that the florets of CL capitula evolved fr om the outermost fertile florets of CH capitula.