PRINCIPLES OF COMPARATIVE STOMATOGRAPHIC STUDIES OF FLOWERING PLANTS

Numerous unsolved taxonomic problems have caused systematists to go beyond the traditional methods of herbarium taxonomists and begin to utilize laboratory disciplines such as cytology, palynology, chemotaxonomy, and anatomy. The anatomy of wood and of leaves, among other things, have been used to provide data for systematic studies. The study of the morphology and ontogeny of the stomatal complex in leaves has been one fruitful area for research. The reader is warned that the taxonomic value of such leaf epidermal characters is very different in different taxa just as is true for traditional morphological characters. The terminology used for describing stomates and the whole stomatal complex or apparatus, as it has developed since the time of Vesque (1889) is given. The classifications of Vesque and Metcalfe and Chalk for angiosperms, and that of Florin for gymnosperms are given in detail. The problems inherent in including the ontogenetic development of the stomatal complex in the description and terminology of types are discussed. It is concluded that morphological classification of stomates is best based on their appearance in the mature leaf, excluding any attempt to include ontogeny as well. Fourteen morphological types of stomates are now recognized: anomocytic, anisocytic, paracytic, diacytic, actinocytic, encyclocytic (cyclocytic), tetracytic, pericytic, desmocytic, polocytic, staurocytic, hemiparacytic, laterocytic, and stephanocytic. Other kinds seen in the literature are subtypes of these. In actuality, intermediates between these types exist in nature, and it is not always easy to distinguish these types. Nonetheless, stomatal types and their ontogenies have been used with success in the resolution of many taxonomic problems. The author outlines the many difficulties encountered in the utilization of such data. Even so, examples from the Celastraceae, Chloranthaceae, Polemoniaceae, Hydrophyllaceae, Boraginaceae, Convolvulaceae, Solanaceae, other dicotyledonous families, and some monocotyledonous families are given. The paracytic stomatotype is regarded as probably primitive in both dicotyledons and monocotyledons. Other types of stomates have repeatedly been derived from the paracytic type, so that the presence of similar advanced stomatotypes is not a sure indication of close relationship.