How does a lycophyte spore develop into a new plant?

In lycophytes, the development of a spore into a new plant depends on whether the species is homosporous or heterosporous. This process involves an alternation of generations between a spore-producing sporophyte and a sex-cell-producing gametophyte.1

Homosporous Lycophytes

In the family Lycopodiaceae (e.g., Lycopodium), spores are identical and germinate to form bisexual gametophytes. Depending on the species, these gametophytes develop in two ways:12
* Surface growth: Some form small, green, lobed plants on the soil surface, maturing in eight months to a year.12
* Subterranean growth: Others develop underground, relying on a symbiotic fungus for nutrition. These are long-lived and may take up to eight years to reach sexual maturity.12

Heterosporous Lycophytes

Genera such as Selaginella and Isoetes produce two types of spores:12
* Microspores: Develop into male gametophytes.2
* Megaspores: Develop into female gametophytes.2

In these plants, development is often endosporic, meaning it begins within the spore wall. The gametophytes are microscopic and lack chlorophyll, relying on nutrients stored within the spore. After fertilization, an embryo develops, initially nourished by the gametophyte tissue via a specialized structure called a haustorial foot, before the sporophyte becomes independent.12