Main Events of Plant Evolution (20):

• Plants evolved from Green Algae; from a group called the Charophytes
• It is believed that ancestral Charophytes lived in shallow water that often dried up

       -Natural Selection would have favored waxy cuticles and layers of tissue surrounding embryos to protect plants from             drying out

• These pre-adaptations paved the way for the transition onto land
• In order to move onto land, early plant ancestors had to change their mode of reproduction to suit life on land

       -gametes became contained within gametangia
       -the egg became fertilized within a female gametangium

• Keeping the embryo contained is a fundamental difference between algae and plants
• Early land plants had no competition with other plants nor were they preyed upon by herbivores

       -therefore, natural selection quickly dictated the expansive diversification of plants

• The first land plants lacked vascular tissue (like modern mosses) so they were limited in ability and size
• Root and shoot development and specialization quickly followed and this required the development of a vascular system
• Early vascular plants had begun to diversify by 400 mya
• In the Carboniferous period, large ferns and other seedless plants dominated the Earth
• Next came the transition from homospory to heterospory; since homosporous plants required water for fertilization, they were limited to damp areas or environments; heterospory allows plants to expand to different environments (not dependent on water)
• Heterospory led to the development of the seed which gave the new evolving plants more freedom since they now had a protected embryo capable of mobility and dormancy
• Among seed plants, some developed flowers and fruits which furthered the survival and success rate of the seed to propagate the new plant generations
• These plants, angiosperms, now represent over 235,000 species versus gymnosperms which only include 700 species

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