Thalia geniculata L. (MARANTACEAE): A PLANT THAT PRODUCES A PSEUDANTHIUM WITH TWO FLOWERS, TWO OVARIES BUT JUST ONE FRUIT

Thalia geniculata L. (Zingiberales, Marantaceae) has inflorescences with two simultaneously opening, hermaphroditic, single-day flowers, which form a pseudanthium. The species has an irreversibly explosive pollination mechanism. In one population of T. geniculata we verified that in 98.5% of the pseudanthia, only one flower from each pair set fruit. We assessed whether this fruit-set pattern could be linked to pollinator behavior, testing if pollinators only visit one flower in each pseudanthium, which would decrease visitation probability of the other flower in the pseudanthium. In the morning, less flowers were visited than in the afternoon, and we observed higher pollinator activity in the afternoon. In the morning, most of the visited pseudanthia had only one flower visited, while in the afternoon most pseudanthia had both flowers visited, the opposite of what we predicted. We concluded that single fruit set in the pseudanthia is not caused by pollinator behavior. It might be caused by pollen limitation during pollinator visits or even  resource limitation to support two fruits per pseudanthia.