Blechnum, commonly known as hard fern, is a genus of ferns in the family Blechnaceae (order Polypodiales), placed in the subfamily Blechnoideae under the Pteridophyte Phylogeny Group classification of 2016 (PPG I). The genus has been subject to two very different circumscriptions: under the narrow PPG I system, Blechnum comprises around 30 species and is one of 18 genera in the subfamily; under a broader definition (Blechnum s.l.), it encompasses roughly 250 species and is one of only three genera recognised in the subfamily. The PPG I concept is mostly neotropical in distribution, with a small number of species from southern Africa.
Plants in Blechnum (sensu PPG I) are predominantly terrestrial or saxicolous (rock-dwelling), with very few epiphytic species. Their rhizomes can be upright or creeping and bear scales with entire or nearly entire margins. A characteristic feature of the genus is the regular production of stolons. The sterile and fertile fronds are usually similar in form, with blades that are pinnatisect or unipinnate and rarely entire. Leaf venation is typically free, with veins dividing one to three times and terminating near the frond margin in enlarged tips. The spore-bearing sori are protected by indusia (scale-like coverings). Well-known members of the genus include Blechnum spicant (deer fern), a widespread species of temperate woodlands in the Northern Hemisphere.
Distribution
In the narrow PPG I circumscription, Blechnum is primarily a neotropical genus, with its roughly 30 species concentrated in Central and South America and a small number of species in southern Africa. Under the broader Blechnum s.l. concept, the approximately 250 species span a much wider range across tropical and subtropical regions worldwide.
Taxonomy Notes
The genus Blechnum is treated very differently depending on the authority followed. The Pteridophyte Phylogeny Group (PPG I, 2016), following Gasper et al. (2016), recognises a narrow Blechnum of about 30 species within a subfamily Blechnoideae of 18 genera. Other authorities use a broadly defined Blechnum s.l. that subsumes most of those segregate genera, recognising only two others in the subfamily and placing roughly 250 species in Blechnum. Regardless of circumscription, the genus sits in family Blechnaceae, order Polypodiales, class Polypodiopsida.
