Comparative Rapidity of Evolution in Various Plant Types

The most recently evolved element in the floras of temperate North America and of Europe, as determined by a study of the indigenous endemic genera, is composed almost entirely of plants which are herbaceous in habit. 2. Herbs tend to be grouped in fewer and larger genera and families than woody plants. 3. It is therefore concluded that herbaceous plants, presumably because of the brevity of their life cycle and the rapid multiplication of generations consequent thereto, are in most cases undergoing evolutionary development much more rapidly than are trees and shrubs. 4. From this conclusion are drawn inferences as to the origin of the herbaceous habit and the antiquity of the Angiosperms.