Asplenium is a genus of about 700 species of ferns, often treated as the only genus in the family Aspleniaceae, though other authors consider e.g. Hymenasplenium separate. A few species are occasionally placed in the separate genera Camptosorus, Ceterach and Phyllitis, but these species can form hybrids with other Asplenium species and because of this are usually included in a more broadly defined Asplenium. Some classifications elevate the Aspleniaceae to an order Aspleniales.
It has been found that in some species, the chloroplast genome has evolved in complex and highly unusual ways. This makes standard cladistic analyses unsuited to resolve the phylogeny of that particular group of ferns, and even very sophisticated computational phylogenetics methods yield little information. In addition to hybridization running rampant in parts of this genus, there are also some species like the Mother Spleenwort (A. bulbiferum) or A. viviparum which mainly reproduce asexually, essentially cloning themselves over and over again. While most are diploid or tetraploid, some species (e.g. A. shuttleworthianum) are octoploid.
The most common vernacular name is spleenworts, applied to the more "typical" species. A. nidus and several similar species are called bird's-nest ferns, the Camptosorus group is known as walking ferns, and distinct names are applied to some other particularly well-known species.
A few of these ferns have some economic importance in the horticulture trade. The bird's-nest ferns (A. nidus and several very similar, closely related species) are commonly found for sale as a house plant. The Australian Mother Spleenwort (A. bulbiferum is sometimes available at greenhouses, and is of interest, along with the related A. viviparum, for the many small bulblets borne on the fronds that may grow into new plants. This characteristic is also shared with the eastern North American Walking Fern (A. rhizophyllum) and several Mexican species including A. palmeri. The Ebony Spleenwort A. platyneuron is also sometimes sold in nurseries as a hardy plant. However, many spleenworts are epipetric or epiphytic and difficult to cultivate.
Asplenium species are used as food plants by the larvae of some Lepidoptera species including Batrachedra bedelliella which feeds exclusively on A. nidus. For diseases of Asplenium, see List of foliage plant diseases (Polypodiaceae).