Bow to the middle: reproductive system and style behaviour of Tococa guianensis, a widespread Melastomataceae from the Neotropics

Floral monosymmetry appears to be a derived condition, arising independently many times, with a multiplicity of forms, and related to both, pollinator and plant diversification. It reduces interference between sexual functions in flowers and increases cross-pollination and allogamy. But since the description and assessment of the functioning of those floral features depend on fresh material and field observations, the number of groups thoroughly observed is limited. In the mostly Neotropical and actinomorphic Melastomataceae, monosymmetric flowers seem to be derived and the resulting herkogamy may constitute a mechanism to avoid anther–stigma interference and self-pollination. Here we studied Tococa guianensis, a Neotropical widespread shrub or treelet well known for its leaf–domatia ant interaction, but still lacking details on its breeding biology. We studied a population in Uberlândia, Central Brazil, observing floral biology features, diversity of visitors and breeding system. Flowers showed diurnal anthesis and a single-day life span. Pollen was the only floral resource offered, and poricidal anthers were clustered in the centre of the flower, while style was bent away from flower axis creating a transient herkogamy and flower monosymmetry. Style moves towards the floral axis during the day facilitating pollination. To date we do not know other Tococa species displaying such stylar features, which may be an intermediate form between the actinomorphic Miconieae and specialized zygomorphic Tococa. Contrasting with previous studies, the self-incompatibility found in T. guianensis indicates that transient herkogamy may function to avoid stigma clogging with self-pollen and allow flexible use of specialized buzz-pollinating bees.