Studies in the comparative anatomy of the Clethraceae

Abstract

These 20 species represent collections form the almost world wide distribution of this family. Anatomically all species studied were found to be homogeneous showing a gradual advancement from the most primitive species studied to the most advanced. From a morphological and geographical viewpoint three groups are recognized. The Clethraceae is generally considered to have but one genus, Clethra L. Results of this study show this to be a valid classification. The Clethraceae appears to be monophyletic in origin. Close relatives of the Clethraceae are thought to be the Theaceae and the lower Ericaceae.