Lycophytes

Lycophytes, or Lycopodiophyta, are a division of vascular plants comprising three living lineages: Lycopodiaceae (club mosses), Selaginellaceae (spike mosses), and Isoetaceae (quillworts). They are among the oldest surviving lineages of land plants, with a fossil record extending back to the Silurian. Today they are small, herbaceous plants found worldwide in temperate and tropical regions, typically in moist forests, bogs, and wet grounds, and in some cases in shallow waters.

A defining feature of lycophytes is their microphylls, small leaves with a single unbranched vein. The sporophyte is the dominant life stage and may be creeping or upright, often with underground rhizomes. Sporangia are produced on specialized leaves called sporophylls, and in many species these sporophylls are aggregated into strobili (cones). Reproduction is by spores rather than seeds. Most Lycopodiaceae are homosporous, producing one type of spore that gives rise to a bisexual gametophyte. In contrast, Selaginellaceae and Isoetaceae are heterosporous, producing distinct megaspores and microspores that develop into separate female and male gametophytes, which are often reduced and can be mycotrophic or subterranean.

Ecology and evolution: Lycophytes were ecologically dominant in some Paleozoic forests and contributed to coal formation. Today, modern lycophytes are relatively limited in diversity compared with other vascular plants, but they occupy a range of habitats from forest floors to wetlands. They are of interest for understanding early land plant evolution and, in horticulture, are cultivated for ornamental foliage in some settings.