Floral biology of Cereus fernambucensis: a sphingophilous cactus of restinga

The family Cactaceae is widely distributed in North and South America, with approximately 1500 species, northeastern Brazil being the the third most important centre of diversity The family is zoophilous, having many groups of animals as pollinators, including bees, beetles, hummingbirds, sphingids, and bats. Pollination by sphingids was observed in a natural population of Cereus fernambucensis Lem. in restinga (coastal sand-dune) vegetation, district of Cabedelo, Paraíba state, NE Brazil. The flowers of C. fernambucensis are white, salver-form, with a long tube (c. 8–15 cm), the expanded perianth-segments forming a bowl shape. Anthesis begins around 23:00h, and at about 02:00h the flowers are completely open. The stamens are numerous and surround the style. Nectar is produced and stored in the nectariferous chamber located at the basis of the flowertube. The average nectar volume is 100 µl, and its sugar concentration is about 24%. The flowers of C. fernambucensis are visited by the sphingid Cocytius antaeus. Visits begin only when the flowers are fully open and last until 04:00h. The interval between visits is 40 minutes. The sphingid alights on the flower and introduces its proboscis into the floral tube, contacting the reproductive organs with the front part of the body and with the tongue. In the morning, from 04:30h, Apis mellifera visits the flowers of C. fernambucensis with regularity, until 06:00h. Although C. fernambucensis is a self-compatible species, the development of fruits was not observed from spontaneous self-pollination. Comparing the results obtained by cross-pollination (85%) with that obtained by hand self-pollination (45%), it is suggested that the xenogamy is the most effective system of reproduction in this species. Comparing the behaviour of sphingids and bees, with the number of developed fruits under natural conditions, it is probable that the flowers of C. fernambucensis use two different classes of pollination vectors: nocturnal visitors (sphingids) and diurnal visitors (bees).