One of the key synapomorphies of the land plants is development from an embryo that is protected by tissues of the parent plant. For this reason, land plants are sometimes called embryophytes (phyton, “plant”). The green plants, the streptophytes, and the land plants have each been called “the plant kingdom” by different authorities; others take an even broader view and include red algae and glaucophytes as “plants.” To avoid confusion in this chapter, we will use modifying terms (e.g., “land plants” or “green plants”) to refer to the various clades of Plantae shown in Figure 27.1.

The land plants that exist today fall naturally into ten major clades (listed by their common names in the center column of Table 27.1). Members of seven of those clades possess well-developed vascular systems that transport materials throughout the plant body. We call these seven groups, collectively, the vascular plants, or tracheophytes, because they all possess fluid-conducting cells called tracheids (discussed in more detail in Chapter 34). The remaining three clades (liverworts, mosses, and hornworts) lack tracheids and are referred to collectively as nonvascular land plants. Note, however, that the three groups of nonvascular land plants do not form a clade (unlike the vascular plants, which are a clade).