5 - Evolution and systematics

Abstract

Systematics is a broad field of inquiry that uses the characteristics and data from many disciplines for describing, naming, classifying, identifying, and determining relationships among plants. Anatomy broadens the base of systematic investigations by providing another set of characters that indicate relationships in harmony with external features. As with morphological characters, some anatomical features are useful in determining phylogenetic trends, whereas others delimit families, genera, or species. The secondary xylem has proved to be highly significant in elucidating higher-level plant phylogenies. One of the greatest achievements of plant anatomy has been the elucidation of the origin and subsequent trends of specialization of the angiosperm vessel element. The angiosperm vessel elements have been phylogenetically derived from scalariform-pitted tracheids by the progressive loss of pit membranes in the regions of tracheid overlap. The methodology of cladistic analysis has become the most widespread approach to modern phylogenetic reconstruction. A hypothesis of the relationship between two or more taxa is based on their shared possession of a derived character state. Anatomy provides important derived character states for the recognition of closely related taxa.