Why do some club moss gametophytes live underground?

In many species of club moss (family Lycopodiaceae), the gametophyte is subterranean and lacks chlorophyll, meaning it cannot produce its own food through photosynthesis. To survive and continue growing, these underground gametophytes rely on a symbiotic relationship with an associated fungus for nutrition.12

These subterranean gametophytes are typically slow-growing, often requiring five or more years to reach sexual maturity. They vary in shape—appearing carrot-shaped, rod-shaped, or disk-shaped—and generally remain underground throughout their development. This life cycle is distinct from other species of club moss that produce small, green, lobed gametophytes that grow on the soil surface.2