Wall

Spore walls may be thick or thin. Thick-walled spores are capable of surviving for a number of years, in some cases up to several decades. Sporocarps (masses of sporangia) of 100-year-old waterclover (Marsilea) have been successfully germinated. Most natural germination of fern spores (except for water ferns) occurs on exposed damp surfaces of rock, on soil, or on dead plant materials.

A number of fern genera (e.g., Osmunda and its relatives, Grammitis and its relatives, Hymenophyllum, Trichomanes, Matteuccia, and Equisetum) possess thin-walled spores. In practically all known examples, such thin-walled spores are also green-pigmented, being provided with chloroplasts. Such spores are common among rainforest genera; they are often short-lived and require a short time for germination. Spores of Hymenophyllum, Trichomanes, and Grammitis remain viable only a few days, those of Osmunda and Equisetum a few months.