Species of Alsophila have a treelike growth habit, with an erect trunk that rarely branches, or sometimes a more shrublike habit, with a creeping stem. Their fronds are large, with a strawlike stalk (stipe), dark brown or black in colour. Brown or dark brown scales are present, with distinct margins. The blade (lamina) of the frond is divided one to three times (one- to three-pinnate). The sori (spore-producing structures) are rounded and borne on smaller veins on the lower surface of the frond. An indusium (a covering to the sori) may or may not be present; if present initially, it may be lost as the frond ages.
Alsophila is now separated from the other genera in the family Cyatheaceae primarily on the basis of molecular phylogenetic studies. The scales on the stalks (petioles) provide a morphological distinction. Alsophila has scales with distinct margins, unlike Sphaeropteris, and with an apical hair or spine (seta), unlike Cyathea. The ornamentation of the spores also distinguishes Alsophila and Cyathea.
The genus Alsophila was erected by Robert Brown in 1810. It is placed in the family Cyatheaceae. The division of the family into genera has had a long and controversial history. Three or four clades have been suggested based on molecular phylogenetic studies. The Pteridophyte Phylogeny Group classification of 2016 (PPG I) accepts three genera, placing the Gymnosphaera clade within Alsophila. In 2018, Dong and Zuo proposed the relationship shown in the cladogram below, and provided names in Gymnosphaera for species they considered to belong in this genus.
The Pteridophyte Phylogeny Group classification of 2016 (PPG I) accepts the genus Alsophila with 275 species. As of August 2019 , the Checklist of Ferns and Lycophytes of the World accepted the following species:
The genus Alsophila is native in tropical and subtropical areas, from North and South America, through Africa, Madagascar and tropical Asia, to eastern Australasia as far south as the subantarctic Auckland Islands. It is found in moist montane forests, on slopes or in ravines, forming part of the lower canopy, middle understorey, or ground layers.
Alsophila species all require frost-free or virtually frost-free, permanently moist, shaded conditions. Those which have been grown in Europe outside their native habitat include A. australis, A. cunninghamii, A. dealbata, A. leichhardtiana and A. rebeccae. Other species are grown in their native regions. In Australia, A. australis is commonly grown and is a robust species, capable of tolerating some sun if kept in moist soil.A. dregei is a popular garden plant in South Africa, with plants being collected for use from the wild sufficiently often to cause it to become extinct in some areas.
In the 1971 comedy film A New Leaf, Henrietta Lowell (played by Elaine May) is a botanist whose dream is to classify a new species of fern. On a honeymoon trip, she indeed discovers a new species which she names Alsophila grahami after her new husband Henry Graham (Walter Matthau). She describes the plant as having a vestigial indusium.