A Comparative Approach to Floral Ontogeny in Melastomataceae

Abstract

The floral diversity of Melastomataceae is stunning and clearly expressed in sepal and stamen structure and in the position of the ovary. Comparative developmental studies are effective in order to understand these variations because they reveal the often-enigmatic origin of the structures. The diverse calyx structure originates from variations in the degree of union between the sepals. The contort corolla aestivation, widespread in the family, is influenced by the floral architecture. Stamen size and shape depend on the space available in the floral bud after the growth of the perigynous hypanthium that may cause the delay in stamen emergence and flexion. Dimorphic stamens originate from differences in their developmental time and position. Prolonged connectives and most of their appendages are formed late during floral development. Ontogeny also explains the decrease or increase in organ number. The intercalary meristems can promote the formation of a hypanthium associated with the gynoecium, and their extension is responsible for the gradual variation in ovary position. These meristems also act on the development of a perigynous hypanthium. Thus, intercalary meristems play an important role for floral diversification in Melastomataceae. The potential of comparative floral development is wide and is illustrated here through several examples in this family.