It is, however, not commonly known by this scientific name. Most resources online and in print will use Blechnum spicant. However, a 2016 paper by Gasper et al., Molecular phylogeny of the fern family Blechnaceae (Polypodiales) with a revised genus-level treatment, asserts this should no longer be the case. To summarize the changes, the authors published an additional paper, A classification for Blechnaceae (Polypodiales: Polypodiopsida): New genera, resurrected names, and combinations where they state in the abstract:
The fern family Blechnaceae, with about 250 species, has traditionally comprised one large genus, Blechnum, plus seven to nine smaller genera, most with fewer than 10 species. Several phylogenetic analyses strongly suggest that Blechnum in the traditional sense is not a monophyletic group. We propose a new classification for the family, with three subfamilies and 24 genera.
Or, perhaps a more approachable (and open-access) summary of the changes is available courtesy of the British Pteridological Society: A New Classification of Blechnum. Interestingly, the author of that article states, “Our native Hard Fern (Blechnum spicant) becomes Struthiopteris spicant a name that was well known in the past”. It seems like a case of what’s old has become new again; first named by Linnaeus as Osmunda spicant in 1753, Friedrich Weiss renamed it to Struthiopteris spicant in 1770. It would be another 2.5 decades before there was a suggestion that this entity belonged in Blechnum. I interpret the words of the author of the BPS article to mean that Struthiopteris spicant was a name used for many years, until it fell out of favour to Blechnum spicant.
Within Struthiopteris (according to the paper above),
…species related to this clade [group] have compact erect stems, with clustered frond rosettes at stem apices. Stems also produce long-creeping rhizomes that grow and form new rosettes. Other morphological characteristics include having strongly dimorphic fronds (but with occasional reversion in S. spicant to the monomorphic condition), pinnatifid sterile blades having many pairs of gradually reduced proximal pinnae
This contrasts with the core Blechnum, which typically have monomorphic fronds. If you are confused by the monomorphic / dimorphic distinction, see the second photograph; the upright fronds are reproductive and distinct from the basal vegetative fronds (and thus dimorphic, or two forms). True species of Blechnum will (typically) only have one physically distinct frond that is responsible for all of the photosynthesis and spore production.
Struthiopteris spicant is an excellent garden plant for temperate shade or woodland gardens. It is recognized as both a Great Plant Pick for our local bioregion and a UK RHS Award of Garden Merit plant for UK gardens. I associate it as a trailside plant along some of my favourite British Columbian rainforest ambles, so I have a particular fondness for it (it also helps that it is perhaps the easiest fern to identify locally when the reproductive fronds are present).