The game of numbers in homeotic flowers ofPhilodendron(Araceae)

Abstract

In Philodendron, pistillate flowers are initiated on the proximal portion of the inflorescence and staminate flowers are initiated on the distal portion. Between the staminate and pistillate flowers, there is a transition zone consisting of sterile male flowers adjacent to the male zone and a row of atypical bisexual flowers between the sterile male zone and the female zone. The portion of the atypical bisexual flower facing the male zone forms stamens, and the portion facing the female zone develops into an incomplete gynoecium with few carpels. The atypical bisexual flowers of Philodendron are believed to be a case of homeosis where carpels are replaced by sterile stamens on the same whorl. In Philodendron melinonii Brongniart ex Regel, Philodendron pedatum (Hooker) Kunth, Philodendron squamiferum Poeppig., and Philodendron solimoesense A.C. Smith, there is a significant quantitative relationship between the number of carpels and the number of staminodes involved in the homeotic transformation in atypical bisexual flowers. On the other hand, such a significant correlation does not exist in Philodendron fragrantissimum (Hooker) Kunth and Philodendron insigne Schott, and Philodendron callosum K. Krause. There is a one to one organ replacement in homeotic flowers in both P. pedatum and P. squamiferum whereas, in P. solimoesense, an average of 2.56 staminodes replace one carpel. The average number of organs developing on an atypical bisexual flower and the number of organs involved in a homeotic transformation appear to be two independent phenomena. The number of carpels in female flowers is correlated with the maximum total number of appendages (carpels and staminodes) that can develop in atypical bisexual flowers.Key words: development, inflorescence, gradient, position, information.