Seedless Vascular Plants Although the tracheophytes include all seed-bearing plants, vascular tissue is also found in many groups of plants that do not produce seeds. Among the seedless vascular plants alive today are three phyla commonly known as club mosses, horsetails, and ferns. DOL•23

The most numerous seedless plants are the ferns. More than 11,000 species of ferns are living today. Ferns have true vascular tissues, strong roots, creeping or underground stems called rhizomes (RY zohmz), and large leaves called fronds, shown in Figure 22–13. Ferns can thrive in areas with little light. They are most abundant in wet, or at least seasonally wet, habitats.

Life Cycle The large plants we recognize as ferns are actually diploid sporophytes. The fern life cycle is shown in Figure 22–14. Ferns and other vascular plants have a life cycle in which the diploid sporophyte is the dominant stage.

In the fern life cycle, spores grow into thin, heart-shaped haploid gametophytes. Although it is tiny, the gametophyte grows independently of the sporophyte. As in bryophytes, sperm and eggs are produced on these gametophytes in antheridia and archegonia, respectively.

Fertilization requires at least a thin film of water, so that the sperm can swim to the eggs. The diploid zygote produced by fertilization immediately begins to develop into a new sporophyte plant. As the sporophyte matures, haploid spores develop on the undersides of the fronds in sporangia, and the cycle begins again.

FIGURE 22–13 Structure of a Fern Ferns are easily recognized because of their delicate leaves, called fronds. Before a frond unfurls, it is called a fiddlehead.

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