Floral Morphology and Phylogeny in the Hydrocharitaceae

The vascular anatomy of 13 of the 15 genera of the Hydrocharitaceae has been studied, and certain aspects of floral morphology are considered. The flowers of the family show a broad range of specialized structures combined with primitive characteristics. The origin of paired and single stamens is interpreted as probable modifications of fascicled stamens. Extreme reduction in the androccium is shown for several genera. Tendencies toward reduction and fusion within the gynoecium are pronounced. Most genera are at least slightly syncarpous, but a few are apocarpous. The inferior ovary is appendicular in nature, with some genera exhibiting more complete fusion than others. The carpels arc open and show no signs of closure. The multicarpellate genera have the most primitive gynoecia within the family while the tricarpe11ate genera exhibit the most advanced types in the family. Intermediate forms are Blyxa and Vallisneria.