Struthiopteris Scopoli 1754

Struthiopteris Scop. (Figure 9D‒H; Figure 14). Type:— Struthiopteris spicant (L.) Weiss. Plants terrestrial; rhizomes erect, not stoloniferous, dark, covered with linear-lanceolate, triangular-lanceolate, or ovate-lanceolate, concolorous or discoloured, chestnut to dark chestnut scales, with sclerosed centre or not, entire margins or with sparse excrescences; fronds dimorphic, subdimorphic (S. spicant var. homophyllum) or monomorphic (S. fallax), sterile fronds with stipes slender, round in section, short, dark, brown, or black, sometimes atropurpureous, with scales proximally similar to those on the rhizome, glabrous distally, striate or densely to smoothly punctate, laminae lanceolate to ovate-lanceolate, 1-pinnate or pinnatifid, gradually reduced towards the base, with glandular hairs on the lamina surface, apices pinnatifid to conform, rachis black to dark brown proximally, grooved adaxially; pinnae adnate, oblong-linear to linear-falcate, with entire margins; costae green, grooved abaxially, prominent adaxially; veins free, simple to 1-furcate, catadromous, ending in adaxial submarginal hydathodes, stomata aligned following veins on abaxial face of pinnae; fertile fronds longer and more erect (in the dimorphic taxa); stipes similar to the sterile ones but much longer, sometimes as long as the laminae, laminae similar in shape to the sterile ones, but with pinnae contracted, with almost not green tissue; rachises and costae as those in the sterile fronds; sori linear, continuous, sometimes interrupted (S. spicant var. homophyllum and S. spicant var. pradae), forming coenosori on both sides of costa; indusia linear, continuous or not, entire; sporangia with 12‒20 arc cells in the ring; spores monolete, perispores brown, irregularly folded. Distribution:— Northern Hemisphere. Northwest America, Europe, the Macaronesian archipelagos and North of Africa and Japan (Figure 1). Basic chromosome number:— n = 34. Taxonomic notes:— The genus most closely related within the family is Spicantopsis. For differences see the Taxonomic notes section of that genus. The other two genera to which it is phylogenetically most closely related are Brainea and Blechnidium (Gasper et al. 2016, 2017, Molino et al. 2019b), however, morphologically they are not similar, these genera presenting anastomosing venation (vs. simple venation in Struthiopteris). Despite not being phylogenetically closely related, it has some resemblance to some species of the genus Austroblechnum, but differs in the margins of the pinnae, which are crenulate to serrate in Austroblechnum and entire in Struthiopteris, however, this difference is not always clear. They also differ in the spores, since in Austroblechnum the perispore is smooth and never has folds, while in Struthiopteris is always folded (Moran et al., 2018, Molino et al. 2020). In addition, Austroblechnum has an austral distribution (Gasper et al. 2016), while Struthiopteris is only found in temple areas of the North Hemisphere. Also, although phylogenetically distant too, it is very similar to Cleistoblechnum. It differs in that the fronds of this genus the margins of the pinnae are strongly revolute (vs. straight in Struthiopteris) and the laminae are more coriaceous.