Intrafloral phenology of Trifolium polymorphum Poir. (Leguminosae) aerial flowers and reproductive implications

Trifolium polymorphum is an amphicarpic species that grows in Uruguay, Argentina, Brazil, Paraguay and Chile. Underground flowers are cleistogamous, obligately autogamous and morphologically highly modified in structure and function. Aerial flowers are chasmogamous, and as mentioned in earlier literature, either allogamous or autogamous. The aim of this study is to identify flower characteristics that facilitate or prevent autogamous or allogamous processes. Floral phenology stages are thus studied in correlation with estimated models of aerial flower development, pollen viability and stigmatic receptivity in three Uruguayan T. polymorphum populations. Flower longevity and development (length, width, and anther-stigma distance), anthesis and anther dehiscence initiation, pollen viability and stigmatic receptivity are the variables correlated with floral phenology. Morphological characteristics of aerial flowers favor autogamy processes - even in pre-anthesis - but phenological characteristics tend to prevent it. The most important reproductive events occurring during flower development, that facilitate autogamous or allogamous processes, are discussed here