The hylocitrea (Hylocitrea bonensis), also known as the yellow-flanked whistler or olive-flanked whistler, is a species of bird endemic to montane forests on the Indonesian island of Sulawesi.Boles, W. E. (2007). Yellow-flanked Whistler (Hylocitrea bonensis). pp. 411 in: Del Hoyo, J.; Elliot, A., & Christie D. eds. (2007). Handbook of the Birds of the World. Vol. 12. Picathartes to Tits and Chickadees. Lynx Edicions, Barcelona. It is monotypic within the genus Hylocitrea. It was traditionally considered a member of the family Pachycephalidae, but recent genetic evidence suggests it should be placed in a monotypic family of its own, Hylocitreidae, related to the waxwings in the family Bombycillidae, the hypocolius in the family Hypocoliidae, the palmchat in the family Dulidae, the silky-flycatchers in the family Ptiliogonatidae, and the now-extinct Hawaiian family Mohoidae (Hawaiian honeyeaters). Some earlier authors took a broader view of this group, treating them as subfamilies in a wider family Bombycillidae, but they are now considered sufficiently diverse and ancient to be classified as a superfamily Bombycilloidea comprising these several families. Within the group, Hylocitrea was found to be a sister group to a clade containing the hypocolius (Hypocoliidae) and the extinct Mohoidae, with the clade containing all three being a sister group to the silky-flycatchers (Ptiliogonatidae). The divergences forming these families occurred in the early Miocene, about 20-23 million years ago.
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