Family of ferns
Blechnaceae is a family of ferns in the order Polypodiales, with a cosmopolitan distribution. Its status as a family and the number of genera included have both varied considerably. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family has 24 genera, and excludes genera placed in the separate family Onocleaceae. The family is divided into three subfamilies, including Blechnoideae s.s. Alternatively, the entire family may be treated as the subfamily Blechnoideae s.l. of a very broadly defined family Aspleniaceae, and include genera others place in Onocleaceae.
Description.
Most are ground dwelling, some are climbers, such as "Stenochlaena". A characteristic feature of many species is that the young opening fronds are usually tinged with red.
Taxonomy.
The family was created by Newman in 1844. In 2014, Christenhusz and Chase submerged it as subfamily Blechnoideae within the family Aspleniaceae and included Onocleaceae in it. The PPG I classification of 2016 restored it to family status.
Blechnaceae is a member of the eupolypods II clade (now the suborder Aspleniineae), in the order Polypodiales. It is related to other families in the clade as in the following cladogram:
Subdivisions.
The number of genera accepted within Blechnaceae (or Blechnoideae when treated as a subfamily) has varied between authors. Christenhusz and Chase (2014), treating the group as a subfamily, describe the situation as follows: "Blechnoideae comprise three major clades, one corresponding to "Onoclea" "sensu lato", a second corresponding to "Woodwardia", sister to all other species that can be treated as the single genus "Blechnum". However, the subclade sister to the rest of "Blechnum" "sensu lato" contains the vining taxa "Stenochlaena", "Salpichlaena" and a few non-vining "Blechnum" species with long-creeping rhizomes, which may have to be accepted at the generic level pending further studies. "Brainea", "Doodia", "Pteridoblechnum" and "Sadleria" belong to "Blechnum" sensu lato."
Perrie et al. (2014) retained the family rank and excluded "Onoclea" as a separate family, Onocleaceae, sister to Blechnaceae. They identified three major clades within the remaining Blechnaceae, which they labelled "Woodwardia", super-"Stenochlaena" and super-"Blechnum", with the latter two as sister groups. They did not consider "Blechnum" as monophyletic and recommended revision of intergeneric boundaries, resulting in seven genera.
Gasper et al. (2016), independently of Christenhusz and Chase, examined the deeper relationships of the 
Blechnaceae, retaining its family status and excluding Onocleaceae, and allocated the three major clades of Perrie et al. (2014) to subfamilies: Woodwardioideae, Stenochlaenoideae and Blechnoideae. Their approach to the polyphyletic nature of "Blechnum" was to create a series of monophyletic segregate genera, resulting in 24 genera in total. The relationship between the three subfamilies was found to be as follows:
The approximate relationship between some of the taxa used in the classifications of Christenhusz and Chase (2014) and PPG I (2016) is shown in the table below.
Subfamilies and genera.
In 2016, the Pteridophyte Phylogeny Group followed Gasper et al. (2016) in accepting 24 genera, grouped into three subfamilies with approximately 265 species, most of which are placed in the subfamily Blechnoideae.
Subfamily Woodwardioideae 
Subfamily Stenochlaenoideae 
Subfamily Blechnoideae 
Subfamily "incertae sedis"
References.
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Bibliography.
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