Psilophyta are the simplest vascular plants. They evolved from rhyniophytes. They have megaphylls, which are multiveined leaves. As stems branched dichotomously, one eventually became the major axis and tissue filled in the side branch to form leaves [Solomon, Berg, Martin, Villee 1997]. They have vascular stems, an underground rhizome covered with rhizoids, and no true leaves. Sporangia, found along the stem, release spores in the soil. These gametophytes depend on symbiotic fungi for nutrients. Flagellated sperm swim through the soil.

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