Cystopteris diaphana (Bory) Blasdell, Mem. Torrey Bot.

Smith, Alan R. & Kessler, Michael, 2018, Prodromus of a fern flora for Bolivia. XXVIII. Cystopteridaceae, Phytotaxa 344 (1), pp. 75-79 : 76-77

Cystopteris diaphana (Bory) Blasdell, Mem. Torrey Bot. Club 21(4): 47. 1963.

Range: —Range uncertain, because of taxonomic confusion with C. fragilis , but throughout Mexico and Mesoamerica (probably also the Greater Antilles), South America (all Andean countries, also at least northwestern Argentina and southeastern Brazil); and eastern and southern Africa and islands the Indian Ocean. In Bolivia, C. diaphana is known from CH, CO, LP, SC, and TA. Sparse molecular data available suggest that “southern” populations of the Cystopteris fragilis complex (including C. diaphana ) form a clade ( C. tasmanica from Australia and New Zealand and C. douglasii from Hawaii being the only exceptions; Rothfels et al. 2013, 2014, 2017), which may be referable to this species. The type is from Réunion.

Ecology: —Common; terrestrial and occasionally epiphytic in humid to semihumid montane forests and alpine habitats, usually in rocky, locally moist and shady habitats, but also on rocky roadside banks, along streams and ditches, and in scrub; 1200–3200(–3750) m, lower in temperate regions and on the Peruvian coast.

Notes: —Specimens of C. diaphana from Bolivia exhibit considerable variation, with small, fully fertile specimens having leaves less than 15 × 2.5 cm (e.g., Kessler 5122, UC) and barely more than 2-pinnate (basal pinnules approaching pinnate-pinnatifid), to individuals with leaves 35 × 6 cm (e.g., Jimenez 1336, UC; Kessler 10478, UC), 3-pinnate-pinnatifid, and sometimes with very narrow ultimate segments <1 mm wide. Similar variants occur in southeastern Brazil (the illustration of Gonzatti 141, RB, by Arana & Mynssen, 2015, of a specimen from Rio Grande do Sul, Brazil, is typical of many in Bolivia) and northern Argentina, as well as northward, into Peru, Ecuador, Colombia, and western Venezuela, and probably into Mesoamerica and Mexico as well. However, specimens of Cystopteris from the southern half of Argentina (to Tierra del Fuego), southern Chile, and Juan Fernández Islands appear to be mostly referable to C. fragilis s.l. (but see below).

Blasdell (1963) accorded C. diaphana a wide range in South America, as well as in Mexico, Central America, the Greater Antilles, and Africa (including offshore islands). He excluded the U.S.A. and Canada from the range, but cited numerous putative hybrids, or introgressants, with C. fragilis from Alaska, Canada, and the U.S.A., and a few from South America (including Bolivia). In temperate North America, these records are now believed to be referable mostly to C. tenuis (Michx.) Desv. , an allopolyploid between elements of a hypothetical diploid ancestor of C. fragilis and C. protrusa (Weath.) Blasdell ( Haufler et al. 1993). The ploidal level of C. diaphana was reported by Blasdell (1963) as n = 42 (diploid), from Chile, and n = 126 (hexaploid), from Costa Rica; counts for C. fragilis are both tetraploid and hexaploid, even occasionally octoploid, from a wide range of localities including Argentina and Peru ( Blasdell 1963). These findings, and many subsequent results by workers in Europe (e.g., Vida 1974, Vida & Mohay 1990) and North America, give a picture of rampant polyploidy and frequent hybridization, resulting in a highly reticulate pattern of evolution in the Cystopteris fragilis complex ( Rothfels et al. 2014, 2017), which includes C. diaphana .