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Evolution in the Plant Kingdom. Illustrate your essay with specific examples.

Introduction

There are four major groups of modern land plant: non-vascular land plants that include mosses , liverworts and hornworts; seedless vascular plants including ferns and horsetails; gymnosperms including conifers and cycads that are characterised by the protection conferred upon the embryo by a hardened seed casing; and angiosperms such that protect and disperse their seeds by flowering or fruiting, reviewed by (Raven et al., 2005), (Mader, 2007).

The evolution of modern land plants from unicellular prokaryotes that acquired the ability to photosynthesise will be discussed here. The evidence in favour of modern land plants sharing a relatively recent common ancestor with algae will also be presented. Additionally, the sequence of evolutionary divergences that have produced modern land plants from their prokaryotic ancestors will be discussed and the adaptations that modern plant groups have evolved in order to successfully exist on land will also be described.

In terms of the success of land plant groups, each group must be well adapted to the environment that it inhabits in order to survive the evolutionary process. In terms of species diversity, angiosperms of the phylum Anthrophyta contain around 250,000 species compared to around 25,000 species of bryophytes (that include the non vascular mosses, liverworts and hornworts) reviewed by (Raven et al., 2005), but in terms of the number of different environmental conditions they inhabit, the non-vascular plants could be described as being the most successful plant group and due to their adaptations in temperature resistance and in maximising small volumes of water, reviewed by (Mader, 2007). Lichens are known to survive extreme desiccation and inhabit a wide range of conditions on Earth, including arctic, boreal and desert environments, reviewed by DePriest, (2004).

Summary

Modern land plants have evolved over billions of years from a unicellular prokaryotic ancestor that underwent endosymbiosis with cyanobacteria and gained the ability to photosynthesise. Divergence from freshwater green algae and movement onto land was followed by the evolution of early land plants into the four modern groups that exist today. Each group of modern land-plants possesses evolutionary adaptations appropriate to the environmental conditions in which they inhabit and each can be described as successful within its own environment.

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