FLORAL DEVELOPMENT OF MONOECIOUS PSEUDUVARIA TRIMERA (ANNONACEAE) AND COMPARATIVE MORPHOLOGY AND STRUCTURE OF ITS STAMENS AND INDEHISCENT STAMINODES

Premise of research. The comparative development of staminate and pistillate flowers in Pseuduvaria trimera (Annonaceae) was investigated for the first time to understand its sexual differentiation and developmental processes. The morphological and anatomical features of mature stamens and staminodes were also compared to clarify anther dehiscence and to understand the mechanism underlying staminode sterility. Methodology. Flowers at different developmental stages as well as mature stamens and staminodes were examined using SEM and LM. Pivotal results. Similar to other Annonaceae, the flowers of Pseuduvaria trimera have a complex whorled phyllotaxis. They have double positions in the outermost whorl of reproductive organs and variable numbers of stamens and carpels per whorl. The stomium region of each theca is composed of the septum and the stomium. The septum and stomium cells of stamens degenerate and facilitate anther opening, whereas those of staminodes remain intact and form indehiscent anthers. Conclusions. The data suggest that staminate flowers are unisexual from their inception while pistillate flowers are morphologically hermaphroditic but nevertheless functionally pistillate. The anthers are indehiscent, and the structural andromonoecy of P. trimera actually functions as monoecy. The mechanism underlying the sterility of the indehiscent staminodes and the delayed dehiscence of the outer stamens might promote xenogamy. The presence of the staminodes is closely correlated with the evolution of functional unisexual flowers in the genus Pseuduvaria.