Meniscium Schreber, Gen. Pl.

Smith, Alan R. & Kessler, Michael, 2017, Prodromus of a fern flora for Bolivia. XXX. Thelypteridaceae, Phytotaxa 331 (1), pp. 1-34 : 25-26

Meniscium Schreber, Gen. Pl. , ed. 8 [a], 2: 757. 1791.

= Thelypteris Schmidel subg. Meniscium (Schreber) C.F.Reed, Phytologia 17: 254. 1968.

A neotropical genus of 25 species ( Fernandes et al. 2014, Fernandes 2015), 13 of which are known from Bolivia. It was monographed by Maxon & Morton (1938), and before that, summarized by Christensen (1913). More recently, Fernandes (2015) and Fernandes et al. (2014, 2016) have dealt with the South American species, and especially those in Brazil, many of which also occur in Bolivia.

Meniscium is easily distinguished and morphologically well defined by having short-creeping rhizomes; monomorphic or subdimorphic fronds (fertile pinnae often narrower and more densely hairy than sterile ones); simple or usually 1-pinnate blades with entire to serrate lateral pinnae plus a ± conform apical pinna; regularly anastomosing veins that form parallel rows of areoles, each areole including either a single free vein or a bisecting vein; and a chromosome base count of x = 36. There are at least 3 areoles and cross-veins (often many more) in a row between costae and pinna margins, and sori are usually confluent (at least in Bolivian species), forming oblong to lunate sori along the cross-veins. Species of Meniscium often grow along streams or even in swampy habitats, at low to, less often, middle elevations. Several species appear to be rather rare and are known from few collections. Meniscium giganteum Mett. , one of only two species of the genus with simple blades, occurs from Nicaragua to southern Peru and is likely to be found in Bolivia.

Meniscium is monophyletic and more closely related, as well as sister, to Cyclosorus s.s. ( Cyclosorus interruptus ) and paleotropical genera Mesophlebion Holttum and Ampelopteris Kunze ( Almeida et al., 2016) than to Goniopteris , which some species mimic. In its distinctive venation, Meniscium is very similar to some species of the paleotropical genus Pronephrium Holttum , but the resemblance is not indicative of a close relationship ( He & Zhang, 2012). Fernandes et al. (2014) made five new combinations for Meniscium species; combinations were already available for other recognized menisciums.

Species of Meniscium are distinguished from one another by a combination of characters: size of fronds; pinna width; pinna bases (cuneate vs. rounded or truncate); pinna margins (entire to undulate to serrate); number of rows of areoles between the costae and pinna margins; sterile areoles about as broad as long, with secondary veins (cross-veins) almost straight vs. much shorter than broad, the cross-veins often curving (subsigmoid); laminar pubescence (hairs spreading vs. adpressed); whether or not sporangial stalks or sterile sporangia (sporangiasters) bear acicular hairs ( Fernandes et al. 2014, 2016; Fernandes 2015). Miocene deposits of a fossil Meniscium have recently been found in Colombia ( Sanín et al., 2016).