DEVELOPMENT AND PHYLLOTAXIS OF THE INFLORESCENCE OF SYMPLOCARPUS-FOETIDUS (ARACEAE)

The inflorescence of Symplocarpus foetidus constitutes good material t o analyse the biological processes and physical constraints involved i n the development of plants. At the adult stage, the inflorescence has an ovoid form. It contains about 65 flowers with a pentagonal or hexa gonal form. The floral primordia appears in alternate rows from the ba sal to the upper part of the inflorescence. Growth zones can be recogn ized, but it is not possible to determine the exact order of appearanc e of successive flowers. The phyllotactic systems observed are 5(2,3), 4(3,4), 2(4,3), 6(1,2), and (9,8). The form of the inflorescence chan ges during growth. In the early stages, when the floral primordia appe ar, the inflorescence is as wide as long. Afterwards, it becomes longe r than wide. The younger primordia have a circular for that they lose when the floral organs begin to grow. The contact parastichies are rec ognized during the first stages of development but, as the floral part s begin to grow, the phyllotactic system loses its regularity. During the development of the inflorescence, two morphogenetic periods can be distinguished (i) before and (ii) during and after the initiation of floral parts. During the first period, when the floral primordia appea r, the phyllotactic system could be explained by global processes at t he inflorescence level. During the second period, the development of f loral parts produces patterns which can be explained by local processe s at the floral level. In this analysis, the author defines the concep ts of open system and closed system in phyllotaxis. In a closed system (e.g., spadix), the elements are arranged on a continuous and closed surface. In an open system (e.g., shoot apex), the elements appear on a surface periodically renewed and are spaced by the intercalary growt h.