Lycophyta: Life History and Ecology

Modern lycophytes are low-growing understory plants, epiphytes, and submerged aquatics -- they are not a significant fraction of the modern vegetation. Their greatest diversity (as with virtually everything else) occurs in the wet tropics, though there are several alpine and subarctic species.

A number of species of Selaginella are known for their survival in extremely xeric conditions. These species occur in the dry, rocky regions of the southwestern United States where they cling to the sides of slopes and along the edges of outcrops, such as the one shown below in Llano County, Texas, near Austin. One species, Selaginella lepidophylla, is so tolerant of drying out that it has been dubbed the "resurrection plant", for it can recover from several months of complete drying. This is uncommon among vascular plants. Many tropical lycophytes experience xeric conditions as well. Those plants which live as epiphytes in the rainforest canopy are subject to intense light and drying winds.

Although they are a relatively inconspicuous component of the modern flora, the lycophytes included large trees of the late Paleozoic. These trees, some of which grew to be more than 35 meters tall, formed forests in the Carboniferous coal swamps of North America and Europe. The large number and good preservation of these ancient plants has allowed us to learn much about their biology, which will eventually be presented in a separate exhibit.

Like ferns and other seedless vascular plants, lycophytes produce gametophyte plants which develop independently of their parent sporophyte. In the club mosses, the gametophyte is usually quite small, and may even develop underground. It relies on a mycorrhizal fungus to help provide nutrients and water. Some of these lycopodalean gametophytes may persist for 15 years before relasing their sperm or producing a sporophyte. Other lycophytes, such as Selaginella, have gametophytes which devlop entirely within the wall of the spore, never venturing out into the environment. These gametophytes may begin their sexual phase while still within the parent's sporangium, producing the new sporophyte generation from within the tissues of the previous sporophyte generation.