Title: Phylogeny - Major evolutionary steps | Britannica
Headings: Major evolutionary steps
Major evolutionary steps
Cyanobacteria, algae, and other early forms of life
Evolution of land plants
Animal evolution
Applications of phylogeny
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Content: Other theories of animal evolutions include their descent from one or more groups of protozoans. Evolution of land plants
Land plants contain two major groups, bryophytes and tracheophytes, which differ in many ways but which share distinctive characteristics for adaptation to dry land. Those include housing the plant embryo in maternal tissue. Bryophytes are descended from green algae and include mosses, liverworts, and hornworts. Only small quantities of water are needed for their reproduction, so that the sperm may travel to the eggs. The fertilized egg matures within the maternal tissue. The plant is protected from desiccation by a waxy cuticle. All the dominant plants on Earth are included in the tracheophytes. The tracheophytes’ development of large plant bodies was made possible by vascular parts that carry water and food inside those plants and by a dominant sporophyte stage (the nonsexual phase in the alternation of generations in the life cycle of certain plants and algae) with a microscopic-sized gametophyte (the sexual phase in the alternation of generations). Tracheophytes’ tissues have differentiated into leaves, stems, and roots and, in the highest plants, into seeds and flowers.