Eriosorus Fée, Mém. Foug.

Kessler, Michael, Smith, Alan R. & Prado, Jefferson, 2017, Prodromus of a fern flora for Bolivia. XXVII. Pteridaceae, Phytotaxa 332 (3), pp. 201-250 : 218-219

Eriosorus Fée, Mém. Foug. 5: 152, t. 13B, fig. 1. 1852.

= Nephopteris Lellinger, Amer. Fern J. 56(4): 180. 1966.

Eriosorus is characterized by creeping rhizomes bearing hairs, glabrous or hairy petioles, blades lacking scales, free veins, and absence of indusia. Hybrids between species are probably frequent in Eriosorus and can make identification difficult; they have intermediate morphology and may have malformed spores (but many suspected hybrids appear to have normal, viable spores). A neotropical, mainly Andean genus of about 30 species (A. Tryon 1970).

The genus is intricately intertwined evolutionarily with Jamesonia , and hybrids with species in that genus are suspected (A. Tryon 1970) but not well documented. Several phylogenetic studies have shown that it may not be possible to separate the two genera (Sanchez B. 2004a, 2004b, Cochran et al. 2014, Pabón-Mora & González 2016). A study by Cochran et al. (2014), including a sampling of several Bolivian species ( E. cheilanthoides , E. elongatus , E. flexuosus , E. hirtus ) does show Eriosorus as a monophyletic clade nested within Jamesonia s.l., but with inclusion of extraterritorial species in analyses, Eriosorus sensu A. Tryon (1970) is not monophyletic. However, we maintain Eriosorus and Jamesonia as separate genera, for expediency and pending further research, because their historical separation, based primarily on blade dissection, is a useful character for recognition. The enigmatic genus Nephopteris , monotypic and known only from Colombia, has recently been shown to be sister to a clade comprising some species of Jamesonia + Eriosorus ( Pabón-Mora & González 2016) ; anatomical characters and conservation status of Nephopteris were studied by González et al. (2015).

All species of both Eriosorus and Jamesonia thus far studied cytologically have shown n = 87, presumed hexaploids on a base of x = 29 (see Löve et al. 1977). This suggests that these genera may have evolved at this high polyploid number, in the last 10–20 million years, perhaps coincident with the uplift of the Andes, which is the major center of diversity in the clade.