Southern Beardless Tyrannulet (Camptostoma obsoletum) - HBW 9, p. 275

Taxonomy: Muscicapa obsoleta Temminck, 1824, Curitiba, Paraná, Brazil.
Forms a superspecies with C. imberbe; the two overlap slightly without intergrading in WC Costa Rica. Numerous races have been described, many of which weakly defined and intergrade broadly with neighbouring ones. Races form five geographically and morphologically discrete groups, within which the various taxa could arguably be merged: Central American (flaviventre, orphnum, majus), N South American (pusillum, caucae, napaeum), W South American (sclateri, maranonicum, griseum), W Amazonian (olivaceum) and C South American (bolivianum, cinerascens, nominate). Some of these groups possibly merit status of full species; this especially true of extreme W Amazonian olivaceum, which sharply bounded on all sides by much paler races and, moreover, is believed to have distinctive vocalizations. Other described races are venezuelae (N Venezuela), considered indistinguishable from pusillum, and bogotense (upper Magdalena Valley, in Colombia), merged with caucae as it represents a barely discernible intergrade between that taxon and pusillum. Thirteen subspecies recognized.