Homeosis in Araceae Flowers: The Case of Philodendron melinonii

Abstract

The early stages of development of the inflorescence of Philodendron melinonii were examined using scanning electron microscopy. Pistillate flowers are initiated on the lower portion of the inflorescence and staminate flowers are initiated on the distal portion. The male flowers have four to five stamens. The female flowers have a multilocular ovary consisting of four to six locules. A transition zone consisting of sterile male flowers and bisexual flowers with fused or free carpels and staminodes is also present on the inflorescences. This zone is located between the male and female flower zones. Generally, the portion of the bisexual flower facing the male zone forms stamens, and the portion facing the female zone develops an incomplete gynoecium with few carpels. In P. melinonii, the incomplete separation of staminodes from the gynoecial portion of the whorl shows that the staminodes and carpels belong to the same whorl. The bisexual flowers of P. melinonii are believed to be a case of homeosis where carpels have been replaced by sterile stamens on the same whorl. At the level of the inflorescence, pistillate and staminate flowers are inserted on the same contact parastichies along the inflorescence; there is no discontinuity between the female zone, the bisexual zone, and the male zone. The presence of bisexual flowers is believed to correspond to a morphogenetic gradient at the level of the inflorescence as a whole.