Based on a single specimen (currently ZMK 1180), Reinhardt and Lütken (1862) described a new species, Leiuperus verrucosus, from near Juiz de Fora, State of Minas Gerais, Southeastern Brazil. In a postscript to the same paper, however, the authors proposed a new genus, Ischnocnema, to accomodate that species, under the combination Ischnocnema verrucosa. For a summary of the taxonomic history and redescription of this species, see Lynch (1972).
With the synonymization of Oreobates JiménezdelaEspada, 1872 to Ischnocnema, this genus also included I. quixensis (JiménezdelaEspada, 1872), as reviewed by Lynch and Schwartz (1971). Later, Lynch (1974), Duellman (1990), Harvey and Keck (1995), and Padial et al. (2005) described I. simmonsi, I. saxatilis, I. sanctaecrucis, and I. sanderi, respectively, completing the six species currently recognized in the genus.
The genus Ischnocnema was distinguished from Eleutherodactylus by Lynch (1971, 1972) and Lynch and Schwartz (1971) mainly on basis of the shape of the distal phalanges: Tshaped in Eleutherodactylus, and knobbed in Ischnocnema. The other characters listed for Ischnocnema by Lynch (1971) are included in the variation of Eleutherodactylus characters, except by the anterior rami of pterygoids reaching the neopalatines in Ischnocnema. Lynch and Schwartz (1971) examined only specimens of I. quixensis, but Lynch (1971, 1972) also examined the holotype of I. verrucosa, although apparently did not observe the condition of its phalanx. Osteological characters listed by Lynch (1971) to the genus Ischnocnema were observed by the author in I. quixensis, the sole species of this genus cleared and stained in his work. The osteological features herein observed in I. verrucosa agree with that attributed to Eleutherodactylus by Lynch (1971) but not with that attributed to Ischnocnema by this author. These findings permit the association of I. verrucosa, type species of the genus Ischnocnema, with the genus Eleutherodactylus.