The sole member of the genus Tyrannopsis, the relationships of Sulphury Flycatcher have proven somewhat difficult to elucidate, even with the advent of molecular techniques. It resembles some speices of kingbird (Tyrannus), but has been considered to be most closely related to the genera Conopias, Myiozetetes, or Megarynchus. Sulphury Flycatcher occupies a wide range over much of Amazonia, as well as in pre-Amazonian savannas, especially at the southeast edge of the range of the species. Sulphury Flycatcher perhaps is most easily detected by its voice, which has been most appropriately described as an 'electrified screeching', and which permits Sulphury Flycatcher to be readily separated from other equally dull-looking tyrant-flycatchers. Throughout its range, Sulphury Flycatcher is closely tied to moriche or buriti palms (Mauritia), but it is not exclusively dependent upon them. Nonetheless, nests are usually placed in palms.