Hierarchical developmental morphology: the case of the inflorescence of Philodendron ornatum (Araceae)

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron ornatum. The development of the inflorescence of P. ornatum can be divided into two morphogenetic phases: (i) before and (ii) after the initiation of the floral organs. Before the initiation of the floral organs, the ratio between the width and the length of the inflorescence is greater than after their initiation. The first phase corresponds to the establishment of the phyllotactic pattern, and the second phase corresponds to the differentiation of floral organs. Pistillate flowers are initiated on the lower portion of the inflorescence, and the staminate flowers are initiated on the distal portion. An intermediate zone consisting of sterile male flowers and atypical bisexual flowers (ABFs) with carpels and staminodes inserted on the same whorl is also present. The portion of the ABFs facing the male zone forms staminodes, and the portion facing the female zone develops an incomplete gynoecium with a few carpels. This phenomenon raises the issue of relationships between hierarchical levels and their mutual influence on the developmental morphology of ABFs. In this article, this question is addressed in the context of the basic triadic system developed by Salthe.