Carpelloid stamens in Rubus trivialis Michx

In several plants of Rubus trivialis, selected by chance during a routine collection from a small population, nearly the entire androecium of each flower was composed of carpelloid stamens. The carpels contained two anatropous, unitegmic, crassinucellate ovules attached to the placenta one above the other. The ovule adjacent to the style degenerated while the basal ovule ultimately developed into a seed Megagametophyte development basically followed the Polygonum type. The carpelloid stamens demonstrated a variety of structural modifications several of which markedly influenced vascular distribution. These modifications support the phylogenetic concept that the carpel and stamen are homologous structures. Carpelloidy in the androecium well may represent one of the mechanisms by which unisexuality is derived. The survival of the carpelloid condition is certainly enhanced by apomictic reproduction, a characteristic feature of Rubus.