SHORTER NOTE

Abstract

Asplenium scolopendrium var. americanum (Aspleniaceae) Found in New Mexico, USA.—Asplenium scolopendrium var. americanum (Fernald) Kartesz & Gandhi (the American hart’s-tongue fern) is among the most distinctive and rarest members of the North American fern flora. First discovered near Syracuse, New York by Frederick Pursh in 1807, reports of new populations of this taxon have drawn considerable interest, due to its rarity, unusual distribution, and close relation to the well-known European hart’s-tongue fern, A. scolopendrium var. scolopendrium L. Following Pursh’s initial discovery, additional populations were found in Tennessee (Williamson, Bulletin of the Torrey Botanical Club 6:347–348. 1879), Ontario (Soper, American Fern Journal 44:129–147. 1954), Alabama (Short, American Fern Journal 69:47–48. 1979), and Michigan (Futuyma, American Fern Journal 70:81–87. 1980). Known localities in the United States, where the species is protected under the Endangered Species Act (ESA), are mostly restricted to areas with heavy lake-effect snow on limestone escarpments in the Great Lakes region, with small disjunct populations in limestone sinkholes and caves in the southeastern US. Plants from Mexico and Haiti have sometimes been treated as a distinct variety (in the segregate genus Phyllitis as P. scolopendrium var. lindenii (Hook.) Fernald) or even a different species (P. lindenii (Hook.) Maxon) but little evidence apart from geography has been presented to support their distinctiveness from A. scolopendrium var. americanum, and they have been treated as synonyms of the latter in recent treatments (e.g., Mickel and Smith, Pteridophytes of Mexico, 2004). Even under this broader taxonomic concept, the American hart’s-tongue fern is restricted to a few scattered localities, and no significant range extensions have been reported since the discovery of plants in Nuevo León, Mexico, in 1983 (Arreguı́n-Sánchez and Aguirre-Claverán, Phytologia 60:399–403. 1986). In February 2017, two of us (L. Baumann and E. Weaver) found a population of A. scolopendrium growing in a protected microsite within a small lava tube in El Malpais National Monument, near Grants, Cibola County, New Mexico. The site was discovered during regular surveys of cave features associated with the McCartys lava flow, which comprises the youngest portion of the ZuniBandera volcanic field (Dunbar and Phillips, New Mexico Geology 16: 80. 1994). In February 2020, the five authors coordinated a trip to survey the population and search for additional possible localities. A snowstorm delayed the start of the trip and nearly caused its cancellation, but conditions settled and we were able to get in the field by early afternoon. Even in good weather conditions, finding the A. scolopendrium population would be difficult; reaching it involves a 40km drive and hiking nearly 2km across a lava field of