Variation in Angiosperm Wood Structure and Its Physiological and Evolutionary Significance

Abstract

Angiosperms show extensive variation in wood structure that reflects their evolutionary diversification and adaptation to a wide range of environments. Evolutionary shifts between an herbaceous and woody habit are common and have produced a wide array of growth forms, including herbs, lianas, succulents, trees and shrubs. As angiosperms moved into new environments, wood structure changed to reflect a balance between functions in water transport and storage, carbohydrate and mineral nutrient storage, and mechanical support. The extent and timing of wood production were modified and new cell types were produced in varying pro- portions and spatial arrangements. In particular, taxonomic variation in water con- ducting elements and parenchyma distribution affect a plant’s ability to withstand drought and freezing temperatures. In this chapter, I interpret the evolutionary sig- nificance of variation in angiosperm wood structure with references to biogeogra- phy, phylogenetics, molecular development, ecophysiology and paleobotany. Cell type-specific techniques in gene expression will continue to be key to the study of these processes.