Hartert (1907-1909) differentiated Seicercus (then called Cryptolopha Swainson) from Phylloscopus by its broad bill, similar to that of flycatchers, strongly developed rictal bristles at base of bill, nostrils covered by bristles, and roundish wings. He remarked that some Phylloscopus approached Seicercus, but they are never as broad-billed, and nostril bristles are less developed. Nests are domed (as in Phylloscopus), and eggs generally plain white. In keeping with this rather imprecise generic definition, Seicercus turned out to be polyphyletic. All of its species form part of the Phylloscopus molecular phylogenetic tree topology, but are dispersed to more than one branch (Olsson et al. 2004, Päckert et al. 2004), signifying splits to levels deeper than species [the generic type species of Seicercus is Cryptolopha auricapilla Swainson = Sylvia Burkii Burton = Seicercus burkii (Burton)]. Ernst Mayr (Mayr et al. 1986: 256) was of the opinion that 'Justification of the genus Seicercus is rather questionable. The included species seem to be nothing but tropical Phylloscopus'. Nevertheless, Seicercus is to be maintained until a sound and detailed molecular phylogeny of Phylloscopus and Seicercus together has been worked out. Only then can objective generic (and/or subgeneric) boundaries be set for the complex as a whole.
