The marsh frog (Pelophylax ridibundus) is a species of water frog native to Europe and parts of western Asia.
Taxonomy
History of naming The first scientific description of the marsh frog was published in 1771 and written by Prussian zoologist Peter Simon Pallas, who gave it the scientific name Rana ridibunda after collecting specimens of it during an expedition through the Russian Empire. Pallas did not precisely specify the type locality (where he found the frogs), only noting it as "versus mare Caspium; Volgae et Iaico" (opposite to the Caspian Sea, Volga, and on the Yaik River). A more precise location of "Gurjew" on the north coast of the Caspian Sea (now the city of Atyrau in Kazakhstan) was given in a 1928 publication written by German herpetologists Robert Mertens and Lorenz Müller. However, a 1994 paper by herpetologists Alain Dubois and Annemarie Ohler noted that because Pallas never designated a holotype specimen, a neotype needs to be selected for the species. The restriction of the type locality done by Mertens and Müller is therefore invalid unless a specimen from Atyrau is designated as the neotype, which Dubois and Ohler suggest should be done. Though Pallas initially considered the marsh frog to be a species in the genus Rana, later authors would move it into other genera or treat it as a variant of other species. French naturalist Pierre Joseph Bonnaterre was the first to do so, moving it into Bufo under the name Bufo ridibundus in an encyclopedia published in 1789, and the same classification was used in a book written by German naturalist Johann Gottlob Theaenus Schneider in 1799. The species would later be moved back into Rana but treated as a variant of the edible frog (which formerly had the scientific name Rana esculenta), with Belgian-British zoologist George Albert Boulenger addressing it as Rana esculenta var. ridibunda in works published in 1885 and 1898. The marsh frog would be listed as a species separate from other frogs again in 1891, when German herpetologist Erwin Schulze established a subgenus of Rana called Baliopygus and listed the marsh frog as a species of it, thus naming it Rana (Baliopygus) ridibunda. In a 1986 paper, Alain Dubois stated that frogs of the edible frog species group should be moved into the subgenus Rana, which means the scientific name of the marsh frog would be Rana (Rana) ridibunda. However, Dubois would later divide Rana into 33 subgenera and place this species in the subgenus Pelophylax under the name Rana (Pelophylax) ridibunda. A study published in 2005 further divided the species placed in the genus Rana at the time into several different genera, with those of the subgenus Pelophylax being assigned to the genus Hylarana, thus the marsh frog was considered to be part of this genus under the name Hylarana ridibunda. In 2006, another publication on amphibian taxonomy elevated the rank of Pelophylax from subgenus to genus, a revision which is further supported by a study published the following year, so the scientific name of the marsh frog was recombined once again into Pelophylax ridibundus.
Obsolete names In addition, some marsh frog specimens were formerly thought to represent distinct, separate forms. They have since been found to represent the same species and the taxa erected based on them are thus considered synonymous. German naturalist Johann Friedrich Gmelin established the name Rana gigas in 1789 for a species of frog found in Persia (now known as Iran), but without designating a holotype or even listing what specimens he studied. In a book printed in 1814 (but whose publication was delayed to 1831), Pallas would erect the names Rana cachinnans and Rana caucasica without listing the specimens studied for any of these supposed species. Additionally, he states that his description of R. caucasica is copied from manuscript notes written by Baltic German explorer Johann Anton Güldenstädt, who referred to it as Rana bufoides instead. Because Güldenstädt's notes were never formally published and the two names refer to the same specimens, R. bufoides is objectively a junior synonym of R. caucasica. Baltic German polymath Karl Eichwald declared R. gigas to be a junior synonym of R. cachinnans in 1842, which itself and R. caucasica were synonymised with R. ridibunda by George Albert Boulenger in 1898. In 1837, Russian zoologist Johann Krynicki erected the species Rana dentex based on multiple specimens found along the Podkumok River in Russia, of which two still exist but were noted to be in "bad condition" in 2009. This species would then be lumped with Rana ridibunda by Boulenger in 1898. The name Rana taurica was first published as a synonym of the Rana esculenta (the edible frog) by French biologist Charles Lucien Bonaparte in 1840, who read the name on a label in the Wien Museum, though a 1994 publication considered it to represent the marsh frog instead. Boulenger established the species Rana fortis in 1884 based on his study of German specimens, but would synonymize it with Rana ridibunda the following year. The species Rana florinskii and Rana mangischlakensis were erected in 1913 and 1925 respectively, the former based on specimens from Tomsk, Russia and the latter based on ones from Mangyshlak, Kazakhstan, but both were synonymized with Rana ridibunda in 1994.
Subspecies There is much debate among herpetologists regarding how many subspecies the marsh frog has. Several similar types of frogs have been named and described as separate species, with proponents for their validity considering them to form a species complex. However, some argue that they should be treated as subspecies of Pelophylax ridibundus instead. A phylogenetic study published in 2024 recovered the following subspecies:
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