Androecium diversity and evolution in Myristicaceae (Magnoliales), with a description of a new Malagasy genus, Doyleanthus gen. nov.

Myristicaceae (Magnoliales) consist of 20 genera and nearly 500 species of lowland rainforest trees with a pantropical distribution. They are distinctive in having small, unisexual flowers with stamens fused into a synandrium, which consists of a single whorl of sessile anthers borne around a sterile central column. With its short filaments and more complex anther phyllotaxy, the Malagasy genus Mauloutchia represents a notable exception to this pattern. New scanning electron microscope (SEM) examinaitons of Brochoneura, Cephalosphaera, Knema, Mauloutchia, and Staudtia are incorporated into a broader review of androecium diversity across the family. These new results are discussed in the context of a phylogenetic study of the family, based on combined molecular and morphological data. The unusual synandrium of Mauloutchia, nested among genera with strictly sessile anthers fused to the column, appears to be secondarily derived. Furthermore, the diversity of patterns observed within the genus may be interpreted as the result of a stepwise transformation involving reappearance and elongation of filaments, increase of anther number, and modification of anther phyllotaxy. However, the question of the origin of stamen fusion in Myristicaceae remains unanswered and requires more developmental studies. Finally, a new Malagasy genus of Myristicaceae (Doyleanthus) is described, which is similar to Mauloutchia in most characters but fundamentally different in androecial traits.