Leaf anatomy of a rheophyte, Dendranthema yoshinaganthum (Asteraceae), and of hybrids between D. yoshinaganthumand a closely related non-rheophyte, D. indicum.

The rheophyte Dendranthema yoshinaganthum(Makino ex Kitam.) Kitam. is endemic to a region along the Naka River in Shikoku, Japan. Resembling other rheophytes that have adapted to environments along rivers, D. yoshinaganthumhas narrow leaves. In the native habitat of D. yoshinaganthumin Tokushima, Japan, natural hybridization with Dendranthema indicum (L.) Des Moul. has resulted in a species complex with conspicuous variation in leaf shape and, in particular, in leaf width. In this study, D. yoshinaganthum and hybrids with natural variation in leaf shape were cultivated under identical conditions and the anatomy of their leaves was examined. Variation in leaf width in the species complex was attributable, for the most part, to variation in the number of cells per leaf lamina and also, to some extent, to variation in cell size. This is the first report of natural variation in leaf width that is attributable to variation in both the size and the number of leaf cells.