Aspects of floral development in Philodendron grandifolium and Philodendron megalophyllum (Araceae)

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron grandifolium and Philodendron megalop hyllum. Pistillate flowers are initiated on the lower portion of the inflor escence, and the staminate flowers are initiated on the distal portion. The presence of extracellular calcium oxalate is observed on the surface of im mature stamens of P. megalophyllum. An intermediate zone consisting of ster ile male flowers and bisexual flowers with fused or free carpels and stamin odes is also present on the inflorescences. This zone is located between th e male and female floral zones. In general, the portion of bisexual flowers facing the male zone forms staminodes, and the portion facing the female z one develops an incomplete gynoecium with few carpels. In P. grandifolium, the incomplete separation of some staminodes from the gynoecial portion of the whorl shows that they belong to the same whorl as the carpels. The bise xual flowers of P. grandifolium and P. megalophyllum are believed to be a c ase of homeosis in which carpels have been replaced by sterile stamens on t he same whorl.