Summary Vegetative characters of Isoetes are generally thought to be of little diagnostic value because of their plasticity and limited number of distinctive character states. The neglect of these vegetative features has resulted in incomplete species descriptions and taxonomic confusion. This problem is exemplified by L triquetra, a name based on a single sterile collection, which has previously been assumed, but never shown, to be synonymous with I. andina. A comparative study of ligule morphology indicates that the two names are indeed synonymous. The taxonomy of Isoetes is based to a great extent on the form and distribution of megaspore surface morphology features (ornamentation). While recent studies on the genus (Boom, 1982; Hickey, 1981; Kott and Britton, 1983; Taylor et al., 1975) support the view that such spore features represent the most reliable source of taxonomic information, this dependence on a single suite of characters results in a number of problems. The most obvious is the difficulty in identifying sterile collections. More importantly, however, is that the dependence on megaspore features has been at the expense of adequate and complete characterization and depiction of vegetative character states. In many cases, vegetative characters are considered of limited taxonomic value because of their infraspecific variability or their interspecific uniformity. It has been well documented that many vegetative characters vary as the result of phenotypic plasticity, ontogenetic development and age of the plant. However, ignoring apparently variable characters is not an acceptable substitute for documentation of their variability. Most systematic studies on Isoetes have been provincial in scope and have been primarily concerned with closely related species which show few significant differences in their vegetative features. As a result, characters showing little or no systematic variation for a given region have been neglected despite the fact that they may be of systematic importance to the genus as a whole. Most frequently this problem (one which is compounded by space limitations in many journals) takes the form of abbreviated, incomplete species descriptions which do not include apparently obvious and assumed data. Examples of poorly described character conditions in Isoetes are phyllotaxy and root branching. These two character conditions were considered to be of little systematic value because spiral phyllotaxy and dichotomously branched roots were assumed to be universal throughout the genus. This assumption changed with the publication of L tegetiformans Rury (Rury, 1978), a remarkable species which has a distichous phyllotaxy and unbranched roots. The discovery of I. tegetiformans indicates the need for complete data bases either in the form of species descriptions or discussions of character variability (e.g., Matthews and Murdy, 1969). Another situation supporting the need for better species characterization pertains to the identity of I. triquetra A. Braun. In British Ferns, Hooker (1861) submerged all previously published species of Isoetes into synonymy under the European I. lacustris. In the same article he recognized as distinct a species from Tasmania and another species from Quito, Ecuador. The Ecuadorian species was accompanied by a list of distinguishing characteristics and Spruce's manuscript name, "Isoetes Andina." Isoetes andina is a robust, amphibious