Polystichum

Polystichum is a genus of about 260 species of ferns with a cosmopolitan distribution. The highest diversity is in eastern Asia, with about 120 species in China alone; the region from Mexico to Brazil has nearly 100 additional species; Africa (17 species), North America (15 species), and Europe (5 species) have much lower diversity. Polystichum species are terrestrial or rock-dwelling ferns of warm-temperate and montane-tropical regions (a few species grow in alpine regions). Many ferns of this genus have stout, slowly creeping rootstocks that form a crown, with a vase-like ring of evergreen fronds 30 to 200 centimetres (10 to 80 in) long. The sori are round, with a circular indusium. The stipes have prominent scales. The genus differs from the well-known and allied fern genus Dryopteris in the indusium being circular, not reniform, and in having the leaf blades with asymmetrical segments—one side of the segment is much longer than the other at the base. Several species are grown as ornamental plants in gardens, notably P. setiferum. One species, P. tsus-simense of eastern Asia, is commonly offered as a houseplant. Hybridisation is frequent in the genus, with several named hybrids, including:- Polystichum species are used as food plants by the larvae of some Lepidoptera species including Pharmacis fusconebulosa. Specimens of some of these can be found at the Royal Botanic Gardens, Sydney. Apomixis, the development of an embryo without the occurrence of fertilization, is particularly common among ferns. Apomixis evolved several times independently in three different clades of polystichoid ferns. The genus Polystichum includes, but is not limited to, the following species. In this list, a species name preceded by (=) is considered to be a synonym of the accepted species name above it. Species that were at one time considered part of the genus Polystichum, but are now categorized elsewhere, include: