| Summary: | Abstract The reproductive biology and the pollination of Echinodorus grandiflorus (Cham. & Schltdl.) Micheli were studied in populations native to interior of the State of São Paulo, Brazil. This species blossoms in summer and its flowers offer both nectar and pollen as rewards to pollinators. Nectar is produced in nectaries located at the base of the marginal carpels, opposite the petals. However, the effective pollinators (social and solitary bees), were recorded collecting pollen only. Visits, which can last from one or a few seconds to more than one minute, occur during the whole flower lifespan. Each flower opens at about 5:30 a.m. and lasts circa eight hours. All plants in the studied populations produce only hermaphrodite flowers. Percentage of pollen viability is 75%. The studied populations are self-incompatible and, as a consequence, pollinators are needed to transfer pollen among individuals. In natural conditions and after hand cross-pollinations, all receptacles presented mature achenes. Based on the analyses of pollen tube growth from hand self-pollinated flowers, and as a consequence of achenes abortion circa 30 days after self-pollinations, the populations of E. grandiflorus studied apparently presents a mechanism of late-acting self-sterility.
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