Development and morphology of flowers and inflorescences in Balanophora papuana and B. elongata (Balanophoraceae)

Extreme modification and reduction in floral morphology presents an obstacle to determining the evolutionary relationships and homologies of the holoparasites in Balanophoraceae. Developing flowers and inflorescences of two dioecious species, Balanophora papuana and B. elongata, were compared to each other and to the monoecious B. fungosa. Intermingled with flowers in the male inflorescences are bracts (B. elongata) or bract parts (B. papuana). In the latter, early cessation of bract tip growth results in two half-bracts, which become displaced during inflorescence elongation, thus disproving the view that these bract-like structures are axial in nature. Male flower primordia emerge in positions axillary to the dividing bracts, and both arise in a spiral sequence. This pattern is modified in B. papuana by the formation of pseudowhorls of four. In both species, the staminate flowers consist of a generally four-merous perianth and a synandrium of congenitally fused stamens. Male flower and bract ontogeny (but not pollen sacs) conform to patterns seen in other angiosperms. More problematic are the carpellate flowers whose primordia arise in irregular order between club-shaped, radially symmetrical organs called claviform bodies. The interpretation that these bodies are homologous to the peltate bracts of Helosideae appears plausible, but cannot explain their nonspiral initiation and radial symmetry.