Some treatments merge the genus into Hypsipetes, often together with the rest of the traditional "Hypsipetes group" of bulbuls: Iole, Ixos, Microscelis and Tricholestes. But in this case, the closely related genera Alophoixus and Setornis would probably also have to be included, and as soon as the earliest described genus, Ixos, is merged with another its name would apply.[4]
In fact, Hemixos is not particularly close to Hypsipetes, and a merger is not well justified. mtDNANADH dehydrogenasesubunits 2 and 3 and nDNAβ-fibrinogenintron 7 sequence data puts it closer to (but still well distant from) the streaked bulbul (Ixos malaccensis). But whether that species represents the core group of Ixos – around its type speciesI. virescens (Sunda bulbul or green-winged bulbul) –, or a distinct lineage worthy of separation in a new genus – in which case Hypsipetes might be merged into the core group of Ixos – has not been studied. In any case, though minor, the Hemixos lineage with its stark white throat and light wing patches seems well distinct.[5]
Gregory, Steven M. (2000): Nomenclature of the Hypsipetes Bulbuls (Pycnonotidae). Forktail16: 164–166. PDF fulltext
Moyle, Robert G. & Marks, Ben D. (2006): Phylogenetic relationships of the bulbuls (Aves: Pycnonotidae) based on mitochondrial and nuclear DNA sequence data. Mol. Phylogenet. Evol.40(3): 687–695. doi:10.1016/j.ympev.2006.04.015 (HTML abstract)
Pasquet, Éric; Han, Lian-Xian; Khobkhet, Obhas & Cibois, Alice (2001): Towards a molecular systematics of the genus Criniger, and a preliminary phylogeny of the bulbuls (Aves, Passeriformes, Pycnonotidae). Zoosystema23(4): 857–863. PDF fulltext