Homeosis in Araceae Flowers: The Case of Philodendron melinonii

The early stages of development of the inflorescence of Philodendronmelinonii were examined using scanning electron microscopy.Pistillate flowers are initiated on the lower portion of theinflorescence and staminate flowers are initiated on the distalportion. The male flowers have four to five stamens. The femaleflowers have a multilocular ovary consisting of four to sixlocules. A transition zone consisting of sterile male flowersand bisexual flowers with fused or free carpels and staminodesis also present on the inflorescences. This zone is locatedbetween the male and female flower zones. Generally, the portionof the bisexual flower facing the male zone forms stamens, andthe portion facing the female zone develops an incomplete gynoeciumwith few carpels. In P. melinonii, the incomplete separationof staminodes from the gynoecial portion of the whorl showsthat the staminodes and carpels belong to the same whorl. Thebisexual flowers of P. melinonii are believed to be a case ofhomeosis where carpels have been replaced by sterile stamenson the same whorl. At the level of the inflorescence, pistillateand staminate flowers are inserted on the same contact parastichiesalong the inflorescence; there is no discontinuity between thefemale zone, the bisexual zone, and the male zone. The presenceof bisexual flowers is believed to correspond to a morphogeneticgradient at the level of the inflorescence as a whole. Copyright2000 Annals of Botany Company Flower, development, gradient, inflorescence