Figure 84. This moss life cycle demonstrates generational alternation with a dominant gametophyte stage
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5.3 Reading Resource #3 The Major Divisions of Land Plants Land plants are divided into two major groups based on the presence or absence of vascular
tissue, as illustrated in Figure 85.
Nonvascular plants are those that lack vascular tissue, which is
made up of specialized cells that transport water and nutrients. The bryophytes, liverworts, mosses,
and hornworts are seedless and nonvascular, and likely appeared early in land plant evolution.
Vascular plants developed a network of cells that conduct water and solutes through the plant body.
The first vascular plants appeared in the late Ordovician period (461-444 million years ago) and were
most likely related to lycophytes, which include club mosses (not to be confused with mosses) and
pterophytes (ferns, horsetails, and whisk ferns). Seedless vascular plants include lycophytes and
pterophytes. They do not produce seeds, which are embryos encased in a hard casing that protects
their stored food reserves. The seed plants are the most numerous of all existing plants and thus
dominate the landscape. Gymnosperms, most notably conifers, produce "naked seeds," while
flowering plants, or angiosperms, protect their seeds inside chambers at the center of a flower, are the
most successful. The walls of these chambers later develop into fruits.
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(credit: modification of work by Mariana Ruiz Villareal)
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Figure 85. The major divisions of plants.
Key definitions Producer – an autotrophic organism that may produce biomass for other species to ingest, like a plant
Essential
