This taxon is Not Recognised as a species by BirdLife International.
Alethe diademata and A. castanea (Sibley and Monroe 1990, 1993) were previously lumped into A. diademata following Dowsett and Forbes-Watson (1993), however Upper Guinea diademata is now accepted as a species separate from Lower Guinea A. castanea on account of: large white spots in tail (3); olive brown vs rufous-chestnut mantle to rump (3); black vs dark brown tail (2); juvenile with more clearly marked white chin and belly (u [1 or 2]).
BirdLife International (2016) Species factsheet: Alethe diademata. Downloaded from http://www.birdlife.org on 05/12/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 05/12/2016.