Leaf anatomy of Mallotus and the related genera Blumeodendron and Hancea (Euphorbiaceae sensu stricto )

The leaf anatomy of Mallotus and Hancea (both subtribe Rottlerinae, tribe Acalypheae) and Blumeodendron (tribe Pycnocomeae) from Euphorbiaceae sensu stricto (subfamily Acalyphoideae) was studied in detail on the basis of 84 specimens belonging to 71 species. Some leaf anatomical features do not show much variation; almost all species have a relatively constant dorsiventral mesophyll, paracytic stomata and collateral bundles in the mesophyll. However, the diversity of other characters is great, especially the hair types, and useful in characterizing infrageneric groups. Capitate glandular hairs are characteristic for Hancea , whereas globular to disc‐shaped glandular hairs occur in most Mallotus spp. Glandular hairs are absent in the two other genera. Morphological diversity in globular to disc‐shaped hairs in Mallotus also provides taxonomically important information. Hancea is characterized by the presence of brachysclereids and cristarque cells and by an abundance of columnar and fibriform mesophyll sclereids. Blumeodendron shares with Hancea the presence of brachysclereids and fibriform sclereids, but is further characterized by the presence of giant stomata. In this study, leaf anatomy is used to discuss the infrageneric delimitation of Mallotus and Hancea and to compare these genera with the more distantly related Blumeodendron . © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society , 2012, •• , ••–••.