ferns

Ferns are a group of seedless vascular plants comprising the true ferns and several related lineages. They reproduce via spores instead of seeds or flowers. Most ferns are terrestrial, though many are epiphytic or aquatic, and occur in moist, shaded environments worldwide, from tropical forests to temperate woodlands. The diagnostic features include fronds, or megaphylls, typically divided into pinnae; a creeping underground stem called a rhizome; and a spore-bearing structure often clustered on the undersides of fronds as sori, sometimes protected by a protective indusium. Ferns exhibit circinate vernation; young fronds unfurl as fiddleheads.

Reproduction involves alternation of generations. The dominant plant is the diploid sporophyte, which produces haploid spores in sporangia. Spores germinate to form a small, free-living gametophyte called a prothallus, which bears male and female sex organs. Fertilization requires free water for the sperm to swim to the egg, after which a new sporophyte grows.

Taxonomically, ferns are classified as pteridophytes and form a diverse clade within the vascular plants. They include thousands of species in several orders, with many adapted to moist forest understories, rocky outcrops, or tree canopies as epiphytes. The fossil record shows ferns among the earliest vascular land plants, appearing in the Devonian and reaching prominence in the Carboniferous.

Humans cultivate ferns widely as ornamental plants and in indoor settings; they also play ecological roles in forest ecosystems and can be indicators of ecosystem health. Conservation concerns include habitat destruction and the effects of invasive species on native fern populations.