The developmental basis of floral variation in Drimys winteri (Winteraceae)

Flowers within a tree of Drimys winteri vary markedly in floral organ number and arrangement. This variation can be linked to developmental differences between flowers in different parts of the inflorescence. Floral organ number varies most markedly between terminal and lateral flowers, whereas variation in organ arrangement is correlated with the shape of the flower. Key events during development, including changes in meristem shape and a delay in initiation of petals, allow a remarkable variety of whorled and spiral phyllotactic patterns to arise. Relatively few flowers showed Fibonacci phyllotaxis, which is otherwise very common in plant systems. Variation in divergence angle within flowers is correlated with meristem shape, whereas variation in plastochron ratio is shown to depend both on meristem shape and on divergence angle. Differences in floral morphology are interpreted as the result of an ordered process of initiation of primordia superimposed on variation in the symmetry of the floral meristem. In flowers with more or less circular floral meristems, organs appeared to be initiated sequentially at a regular divergence angle, whereas during early development of flowers with more elliptic meristems there was a preferential initiation of organs toward the poles of the elliptic meristems. This study is the first to examine how variation in floral organ number and arrangement is partitioned within individuals of D. winteri, or indeed any other member of the Winteraceae.