The bryophytes probably are the most recently 

 evolved phylum. The oldest known moss and liver- 

 wort fossils occur in Pennsylvanian rocks, and thus 

 are about 300 million years old. Other phyla gener- 

 ally have remains at least 400 million years old, and 

 most are much older than that. 



Bryophyte features imply their relationship to the 

 vascular plants. Although bryophytes lack true roots, 

 stems, and leaves, their body parts and life cycle are 

 similar to those of the vascular plants; also moss and 

 liverwort gametophytes often resemble those of the 

 more primitive vascular plants. For this reason, the 

 Bryophyta and Tracheophyta regularly are united as 

 the Subkingdom Embryophyta and are commonly 

 called "embryo plants" or "land plants." Prior to 

 discussing liverworts and mosses, we will further 

 examine their possible affinity to the Tracheophyta. 



SUBKINGDOM EMBRYOPHYTA 

 ( Land or Embryo Plants) 



Although the fossil record shows little that can be 

 construed as evidence for a common ancestry of the 

 two Embryophyta phyla (Bryophyta and Tracheo- 

 phyta), these plant groups do have various features 

 in common. 



It should be mentioned that the expression "land 

 plants" is deceiving. Many Algae are land plants in 

 the sense that they are plants and are terrestrial, not 



aquatic. Conversely, many Embryophyta are aquatic, 

 some being completely submerged, and a few are 

 marine. However, the Algae do not comprise the vast 

 majority of the terrestrial flora as embryophytes do. 

 For this reason, and because embryophytes were the 

 most successful plants to invade the land, the use of 

 "land plants" as a descriptive common name for this 

 subkingdom is justified. 



Diagnosis: tissue or organ organization; individual 

 cells of generalized to specialized types derived devel- 

 opmentally from generalized cells; generalized cells 

 with nuclear, cytoplasmic, and cell wall components 

 essentially the same as in the Chlorophyta; body 

 organization of tissues with tissue layering (Bryo- 

 phyta) or organs (Tracheophyta) in the sporophyte; 

 organ systems are not typical of entire land plants 

 but occur in the form of cones or flowers; asexual 

 reproduction without spore formation; life cycle 

 diplobiontic with definite alternation of generations 

 and with sporophyte showing progressively more 

 complex development until the embryo sporophyte 

 is not a parasite upon the gametophyte (some Rhodo- 

 phyta have parasitic sporophytes, but not a definite 

 embryo stage); mostly terrestrial. 



Reproduction: definite sporophyte and gameto- 

 phyte generations. Asexual spores (produced by mito- 

 sis) never are formed; the only spores are formed by 

 the sporophyte and are sexual spores (produced by 

 meiosis); asexual reproduction mostly in gametophyte 



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