Trends in Plant Evolution

Trends in Plant Evolution - conducting cells of the xylem...

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Trends in Plant Evolution Several evolutionary trends within the plant kingdom have been noted. The monophyletic nateure of this kingdom is not in dispute, with the first major division being between vascular and nonvascular plants. Wihin the vascular plants we see increasing changes in the relationship between sporophyte and gametophyte, culminating in flowering plants. Developing from green algal ancestors, plants show a trend for reduction of the complexity, size, and dominance of the gametophyte generation. In nonvascular plants the gametophyte is the conspicuous, photosynthetic, free-living phase of the life cycle. Conversely, the angiosperm gametophyte is reduced to between three and eight cells (hence it is very inconspicuous) and is dependent on the free-living, photosynthetic sporophyte for its nutrition. Plants also developed and refined the root-shoot-leaf axis with its specialized
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Unformatted text preview: conducting cells of the xylem and phloem.The earliest vascular plants, such as Cooksonia and Rhynia , were little more than naked (unleafed) photosynthetic stems. Some plants later developed secondary growth that produced wood. Numerous leaf modifications are known, including "carnivorous" plants such as the Venus flytrap, as well as plants that have reduced or lost leaves, such as Psilotum and the cacti. A third trend is the development of the seed to promote the dormancy of the embryo. The seed allows the plant to wait out harsh environmental conditions. With the development of the seed during the Paleozoic era plants became less prone to mass extinctions. The fourth trend in plant evolution is the encasing of a seed within a fruit. The only plant group that produces true fruit is the flowering plants, the angiosperms. Fruits serve to protect the seed, as well as aid in seed dispersal....
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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