Lycopodiopsida

Lycopodiopsida is a class of vascular plants in the division Lycopodiophyta, commonly referred to as lycophytes. They are among the oldest lineages of land plants, with a fossil record extending back to the Silurian. The class comprises three living orders: Lycopodiales (clubmosses and their relatives), Selaginellales (spikemosses), and Isoetales (quillworts). Most species are small herbs, though some Lycopodiales can form creeping or climbing growth forms. Members typically have microphyll leaves arranged along dichotomously branching stems; many form horizontal rhizomes and, in some species, underground photosynthetic or mycotrophic gametophytes.

Reproduction is by spores; the sporangia are usually borne in specialized structures. Lycopodiales are predominantly homosporous, producing a single size of spore and a free-living, photosynthetic gametophyte. Selaginellales and Isoetales are heterosporous, producing microspores and megaspores with distinct male and female gametophytes, often with more dependence on the sporophyte. The life cycle is dominated by the diploid sporophyte, with gametophytes typically small and short-lived.

Ecology and distribution: lycophytes are widespread in temperate and tropical regions, occupying forests, rocky slopes, and wetlands. Isoetales and many Isoetes species inhabit damp aquatic or semi-aquatic habitats, while Lycopodiales commonly form ground cover in shaded, forested areas. Evolutionary significance: lycophytes were once dominant in Carboniferous forests and contributed to coal formation; today they persist as relicts and provide insight into early vascular plant evolution. The group remains a key lineage for understanding plant morphology and physiology in ancient vascular plants.