Reproductive biology of two Cattleya (Orchidaceae) species endemic to north-eastern Brazil

The reproductive biology of the endemic Cattleya elongata and the endemic and critically endangered Cattleya tenuis (Orchidaceae) was studied in areas of 'campo rupestre' and 'caatinga' vegetation, respectively, in the Chapada Diamantina, north-eastern Brazil. Floral visitors and their behavior were recorded, and experimental pollinations were carried out to determine the breeding systems of these species. The species have similar flower morphology, flower in synchrony and both are pollinated by queens of Bombus (Fervidobombus) brevivillus (Apidae, Bombina). Flowers of both species do not present nectar despite the presence of a nectary-like cuniculus. Cattleya tenuis presented low natural fruit set (10%), while C. elongata presented a higher fruit set (25%). Both species are self-compatible, and only C. tenuis presented inbreeding depression, expressed as reduced seed viability in self-pollinations compared with cross-pollinations. The species have a parapatric distribution and differences in their habitats probably act as the principal barriers to the formation of natural hybrids.