The phylogenetic position of the genus Didymeles has been much debated since its description in the early 19th century. It has been allied with various families such as Leitneriaceae, Fagaceae, Myricaceae, Euphorbiaceae, Thymelaeaceae, Hamamelidaceae, Balanopaceae, Daphniphyllaceae, and Buxaceae. Recent molecular and combined molecular and morphological analyses strongly support the sister relationship of the monogeneric Didymelaceae and Buxaceae and place them in a grade of families at the base of eudicots between ranunculids and core eudicots. Didymeles has two species, which are endemic to Madagascar. They are evergreen, dioecious trees with inconspicuous flowers in axillary compound racemes or thyrses. Flowers are extremely simple. Male flowers are described as being perianth-less and composed of only two stamens; female flowers are reported to have a variable number of scale-like sepals and one carpel. However, many aspects of the structure of inflorescences and flowers are only poorly known; for example, the delimitation of female flowers is debated. In the axil of a bract on the main inflorescence axis, there is a pair of transverse bract-like organs on a stalk. In the axil of each bract-like organ, a carpel is situated. The dorsiventral plane of each carpel is slightly deflected abaxially in relation to the main inflorescence axis. The question arises whether this group of organs corresponds to two unicarpellate flowers as in some Proteaceae, or to one bicarpellate flower as present in some other basal eudicots. Here we present a more detailed study on the structures of female inflorescences and flowers of Didymeles integrifolia and discuss the results in comparison with inflorescences and flowers of the sister family Buxaceae and other members of basal eudicots.

Key words: basal eudicots, Didymelaceae, floral structure, inflorescence structure