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Floral biology of Costus spiralis (Jacq.) Roscoe (Costaceae) and mechanisms to avoid self-pollination

The floral biology of Costus spiralis (Jacq.) Roscoe (Costaceae) was studied on swampy edges of a gallery forest in Uberlândia, Minas Gerais. Costus spiralis is an herb with 0.5 m to 2.0 m in height which blossoms from January to April (rainy season). It presents spirally twisted branches with terminal inflorescences that produce only one flower per day. The flowers are subtended by conspicuous red bracts that can attract pollinators. The flowers are hermaphroditic, red, tubular, odourless and present diurnal anthesis. Concentration of sugars in nectar was c. 20% and volume c. 9.0 µL. C. spiralis is a self-compatible, non apomictic species, which does not present spontaneous self-pollination. It presents movement herkogamy to avoid self-pollination. The pollinators of C. spiralis were the hummingbirds Phaethornis pretrei (Lesson & DeLattre) (Phaethornithinae), Eupetomena macroura (Gmelin) and Heliomaster squamosus (Temminck) (Trochilinae). Amazilia fimbriata (Gmelin) acted as nectar robber. Costus spiralis has a floral morphology adapted to pollination by Phaethornithinae, with a long and curved floral tube which conforms with the beak morphology of these birds. The strategy of trapline foraging by Phaethornithinae hummingbirds, favors the reproduction of the plant, increasing pollen flow between groups of C. spiralis. There was no difference between germination rates of seeds from self-pollination and cross-pollination, but the seeds produced from natural fruit-set presented significantly higher germination rates than those from hand pollination treatments. The results confirm the efficiency and importance of the hummingbirds as pollen vectors for C. spiralis.

breeding system; Costus spiralis; germination; hummingbirds

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