A division (formerly Lycopodiophyta) of the subkingdom Embryobionta which represents one of two main lineages that evolved during the Early Devonian from the earliest land plants to develop vascular tissue and multiple sporangia. Integration of living and fossil taxa has allowed tentative reconstruction of the evolutionary history of the lycophyte group, which is generally regarded as monophyletic (includes all the descendants of a single putative ancestor). The division Lycophyta contains two classes: the extinct Zosterophyllopsida (zosterophylls) and the Lycopsida (club-mosses), which contains 10 extant genera. See also Lycopsida; Zosterophyllopsida.
Living lycophytes are confined to the Lycopsida and are of far less phenotypic diversity and ecological significance than the fossils; most are small-bodied rhizomatous herbs or tuberous pseudoherbs occupying moist niches of low interspecific competition. Their economic significance is confined to various industrial applications of the abundant, small, and unusually uniformly sized spores of Lycopodium. The extant genera represent perhaps half of the major lycopsid groups known in the fossil record.
The lycophytes have a small gametophyte that is morphologically distinct from, and physically independent of, the larger sporophyte. Gametophytes are either supraterranean and photosynthetic or subterranean and saprophytic. The primitive growth habit is unipolar; rhizomes periodically generate adventitious roots and aerial branches. Vegetative branches are small, nonwoody, dichotomously branched, and either naked or, more commonly, scattered with cortical projections. The primary xylem undergoes external maturation. Other key features of the Lycophyta are unvascularized, kidney-shaped eusporangia that are positioned laterally rather than terminating axes. The spores are released through distal lateral dehiscence slits.
The evolutionary history of the lycophytes generally is documented by increases in body size, vegetative complexity, and reproductive sophistication.
