Développement et phyllotaxie de l'inflorescence du Symplocarpus foetidus (Araceae)

Abstract

The inflorescence of Symplocarpus foetidus constitutes good material to analyse the biological processes and physical constraints involved in the development of plants. At the adult stage, the inflorescence has an ovoid form. It contains about 65 flowers with a pentagonal or hexagonal form. The floral primordia appears in alternate rows from the basal to the upper part of the inflorescence. Growth zones can be recognized, but it is not possible to determine the exact order of appearance 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 changes during growth. In the early stages, when the floral primordia appear, the inflorescence is as wide as long. Afterwards, it becomes longer than wide. The younger primordia have a circular form that they lose when the floral organs begin to grow. The contact parastichies are recognized during the first stages of development but, as the floral parts 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 appear, the phyllotactic system could be explained by global processes at the inflorescence level. During the second period, the development of floral parts produces patterns which can be explained by local processes at the floral level. In this analysis, the author defines the concepts 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 growth. Key words: angiosperms, morphogenesis, phyllotaxis, development, model.