Reproductive systems and crossing potential in three species of Bulbophyllum (Orchidaceae) occurring in Brazilian 'campo rupestre' vegetation

Experimental self-, cross- and interspecific pollinations were carried out in Bulbophyllum weddellii, B. involutum and B. ipanemense (Orchidaceae). Th e last two species are closely related, but B. weddellii is somewhat more d istant. The three species are self-compatible, with pollination by a vector necessary for fruit formation. In all crossing types, high rates of fruit abortion and formation of seeds without embryos were observed, particularly in interspecific crosses that involved B. weddellii. Crosses between the m ore closely related B. involutum and B. ipanemense produced fruit formation rates and seed viability similar to those obtained in intraspecific crosse s. These results agree with current hypotheses that suggest that interspeci fic crossing rates reflect phylogenetic proximity. Examination of pollen tu be growth and aborted fruits suggests that a series of factors may be invol ved in the high abortion rate for fruits and large proportion of seeds with out embryos. The low interspecific fertility noted for B. weddellii and B. involutum is important in the maintenance of isolation between these specie s that are sympatric, flower in the same period and share the same pollinat ors.