Comparative floral ontogeny in Winteraceae

The flowers of Winteraceae have often been considered representative of the floral morphology of the earliest angiosperms. The diversity in number and arrangement of the (mostly) free floral organs gives an opportunity to critically examine floral developmental processes in this basal angiosperm family. Comparative ontogeny and morphology of flowers of eight species from six genera of Winteraceae were examined using scanning electron microscopy (SEM) and light microscopy. Results were compared with the floral morphology of Takhtajania perrieri (Capuron) Baranova & J-F. Leroy, the recently rediscovered species of Winteraceae from Madagascar. The analysis showed that the basic floral architecture in the family is one of varying numbers of decussate organs followed by whorls with four (or more) organs. Spiral and irregular patterns also occur, with irregularities in floral organ arrangement often the result of initiation of primordia on an asymmetrical floral meristem. The first organs initiated are a pair of sepals that are usually lateral relative to the subtending bract of the flower. Further growth of the calyx is via a ring of meristematic tissue encircling the floral meristem, producing a tubular calyptra bearing the sepals at its apex. The calyptra either encloses the bud until anthesis (Tasmannia and Drimys) or ruptures while the bud is still young (Zygogynum, Exospermum, Bubbia, Pseudowintera, and Takhtajania). Differences in the position of the sepals relative to the subtending bract and the position of the petals relative to the sepals create differences in floral architecture between taxa. These differences support Tasmannia and Drimys being considered separate taxa and Zygogynum and Exospermum being considered separate from Bubbia. The decussate and whorled floral architecture of Takhtajania perrieri reflects the basic pattern found throughout the family.