Chapter 13 - The Origin and Early Evolution of Green Plants

Abstract

This chapter discusses the origin and early evolution of green plants. The chapter defines green plants and discusses the green plant body plans, and the evolutionary history of some of the basic types. The unicellular flagellate is considered to be the most ancestral green plant body. There are three main sexual life history patterns expressed in green plants. Each type is determined both by the evolutionary history of the species and the environment in which it has evolved. The chapter discusses the core structure of the green plant phylogenetic tree; the archegoniate line, the chlorophyte line, and the prasinophytes. The unresolved nodes in the phylogenetic tree, with special reference to those areas that are most relevant to larger issues of phototroph evolution in aquatic environments are discussed. A brief note on green plants in today's marine environment is also presented. Certain branch points, especially at the base of the tree and at important nodes such as the ones associated with the evolution of the “seaweed” genera and with the early radiations of the archegoniate plants, remain to be resolved. As nuclear genome sequencing becomes more prevalent, comparative data from this source will need to be employed.