Development of inflorescence and flowers of Philodendron acutatum Schott (Araceae)

The inflorescence of Philodendron acutatum possesses female flowers in the inferior part and male flowers in the distal part. The male flowers possess from three to six stamens, rarely seven to nine. The female flowers possess a multilocular ovary comprising from 8 to 12 locules. Each locule corresponds to a closed carpel. The styler canals remain separate up to the upper part of the gynoecium. In this inflorescence, one observes an intermediary zone comprising bisexual flowers with fused or free carpels and stamens, inserted in the same whorl. Generally, the portion of the bisexual flower facing the male zone is formed by stamens, and that facing the female zone is formed by an incomplete gynoecium comprising few carpels. The separation between the two parts of a bisexual flower is generally clear; however, in rare cases, a stamen appears between two carpels, or a carpel between two stamens. Nevertheless, in all cases, the different flower parts are inserted on the same whorl. The presence of bisexual flowers corresponds probably to a morphogenetic gradient at the level of the overall inflorescence. The genes controlling the expression of flower sex are probably governed by chemical processes that act at the level of the overall inflorescence.