HETEROPHYLLY IN HIPPURIS, A PROBLEM IN IDENTIFICATION

Although the primordia of all types of leaves in Hippuris show no distinguishing characteristics until they are 50 microns long, their further development is strongly influenced by their environment. At maturity they can, for convenience, be thought of as belonging to one of five types, or some intermediate of these types. The five types of leaves are: rhizome, juvenile aquatic, adult aquatic, juvenile aerial, and adult aerial. Field and experimental studies indicate that the leaf form in Hippuris is influenced by light and the water relations between the plant and its environment. There is great uniformity of foliar morphology on plants from stocks of diverse origin when grown under uniform conditions, and there is wide diversity of foliar morphology on plants of the same stock material when grown under different environments in the laboratory. Thus the taxonomic subdivision of genus Hippuris into species, varieties, and forms using leaf morphology as the main criterion appears questionable.