Pollen Diversity and Evolution in Myristicaceae (Magnoliales)

Myristicaceae consist of 21 genera and nearly 500 species of lowland rainforest trees with a pantropical distribution. This article presents new scanning electron microscopy observations on pollen of 13 genera, including all Asian genera, which had previously received very little attention from palynologists. While confirming that all Myristicaceae have monoaperturate pollen shed as monads with a sculptured aperture membrane, this study increases our knowledge of the diversity of pollen shapes, aperture shapes, tectal sculpture and microsculpture, and infratectal structure across the family. It also clarifies a few characters in previously investigated Afro‐Malagasy taxa. These results are discussed in the context of a recent phylogenetic study. While several pollen characters appear to be homoplastic, aperture shape, tectal sculpture, and infratectal structure seem to be of great phylogenetic value in Myristicaceae and clearly distinguish an Afro‐Malagasy clade of five genera (including Mauloutchia) from the rest of the family. Contrary to previous assumptions on character polarity, the ulceroid aperture shape and mixed (to granular) infratectum of most species in this clade both appear to be derived features, whereas the common ancestor of Myristicaceae likely was characterized by sulcate pollen with a columellar infratectum. A continuous tectum also clearly sets apart the members of this Afro‐Malagasy clade from the rest of the family, which has a reticulate to rugulate tectum. However, the status of this character in the ancestor of Myristicaceae remains equivocal.