Systematic anatomy of vegetative organs of the Hydrocharitaceae

The anatomy of the Hydrocharitaceae is described in relation to the modes of life of the family. Leaf morphology depends on the ecology of the species. The xylem is simple with relatively primitive characters, but the phloem shows a contradictory evolutionary trend, possessing the highly evolved characters of large, wide sieve-tube elements with more or less horizontal, simple sieve-plates and a single companion cell to each element. Characters of taxonomic value within the family exist but are lewer and less satisfactory than those in families such as the Cyperaceae; such characters are the shape of the axillary scales, the pattern of occurrence of tannin secretory cells and the diaphragm cells of roots. A microfiche of data and plates of illustrations not printed in the journal is available.