The reproductive biology of Ruellia brevifolia was studied in two populations of southeastern Brazil. R. brevifolia is a shrublet that grows in dense clumps in open but shaded areas. This Acanthaceae blooms all year round and produces chasmogamous (CH) and cleistogamous (CL) flowers during the rainy and the dry season, respectively. Cleistogamy is of the "clymatic" type, and produces seeds in the most stressful period of the year. CH flowers are tubular, red and odourless, protogynous, and may be herkogamous or not; anthesis is diurnal, and they last two days. Nectar is produced in small amounts (5.2 mul ± 2.36) and its concentration is about 30%. CL flowers resemble CH buds, except for their pale color. Pollen/ovule ratio of CL flowers is 60% lesser than that of CH flowers because of the small amount of pollen grains. This Ruellia is self-compatible, but protogyny and herkogamy favour allogamy; spontaneous self-pollination in CH flowers seems to be related to the non herkogamous flowers. The hummingbird Amazilia lactea and the butterflies Heliconius etilla narcaea and Phoebis argante are the major pollinators of R. brevifolia. The hummingbirds visit R. brevifolia only during flowering peaks, when there is a high number of flowers. It seems plausible that both the small nectar volume per flower and the trap-line foraging strategy of A. lactea promote mainly outcrossing. The butterflies visit flowers mainly in the same plant group, but during low floral density periods they fly greater distances also favouring outcrossing.
Floral biology; herkogamy; cleistogamy; ornithophily; psicophily
