Development of the inflorescence and flower ofPhilodendron fragrantissimum(Araceae): a qualitative and quantitative study

Abstract

The early stages of inflorescence development in Philodendron fragrantissimum (Hook.) G. Don are 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. Male flowers have 6-8 stamens (sometimes 5) and female flowers have a multilocular ovary consisting of 6-10 locules. A transition zone consisting of sterile male flowers and bisexual flowers with fused or free carpels and staminodes is also present. This zone is located between the male- and female- flower zones. Generally, the portion of the bisexual flower adjacent to the male zone forms staminodes and the portion bordering the female zone develops an incomplete gynoecium with few carpels. The different floral organs of the bisexual flowers are all inserted in the same whorl. Pistillate and staminate flowers are inserted on the same contact parastichies along the inflorescence; there is no spatial 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. A quantitative analysis of a series of parameters (i.e., length and width of flower types and inflorescence zones) indicates that each zone of the inflorescence has its own particular nature as far as rhythm of growth and geometry are concerned. There appears to be evidence for some form of partitioning in the global development of the inflorescence. The growth of a zone seems to be more variable in size and geometry than that of individual flowers. During later stages of development, the size of the flowers of the intermediate zone, especially the sterile male flowers, increases considerably, until it exceeds that of both male and female flowers.Key words: homeosis, morphogenesis, gradient, allometry, reproduction.