Ultrastructural data for the practicing plant systematist

Abstract

During the past decade, ultrastructural data from both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to determine relationships among flowering plants. Modern studies in plant systematics rely upon many kinds of comparative data such as morphology, cytology, cytogenetics, chemistry, and anatomy; and ultrastructure is another important source of information. Practicing plant systematists put most of their efforts into making classifications, which involve grouping and ranking. Ultrastructure appears suitable for use in classification, and it has the advantage of allowing comparisons of structure at the cellular or subcellular level, and this may help reveal homologies more clearly. For systematics of the flowering plants, pollen grains, seed coats, and leaves have been investigated most intensively so far, and the first two have been particularly useful because of their ontogenetic and environmental stability. From leaves, cuticular waxes, generalized epidermal cells, stomata, and trichomes have been studied most frequently. Within stems, sieve-tube plastids have been used as characters at the higher taxonomic levels. In general, those internal features that are best viewed via TEM are those most important at the higher levels in the taxonomic hierarchy. External features viewed best with SEM are more useful at the lower levels. Ultrastructural studies add new potential to systematic research through such efforts as the determination of the adaptive nature of taxonomic characters, and the use of ultrastructure to understand evolutionary dynamics such as ecotypic differentiation and hybridization. © 1979 by the American Society of Zoologists.