Latham (1781) first described the Robust Parrot (original specimen now lost) from J. Banks’ collection which Gmelin (1788) used for his type description of Psittacus robustus. Psittacus is the same genus as the African Grey Parrot (Psittacus erithacus).
The genus Poicephalus was proposed by Reichenow (1881) to replace Psittacus for this African Parrot group. Poicephalus robustus suahelicus (Reichenow) was described as Poicephalus suahelicus (Reichenow) with a specimen from Msua near Bagamoyo, Tanzania (Clancey 1963).
Clancey (1997) proposed P. robustus (which is associated with Afromontane forest habitats) be a separate species from P. fuscicollis. This was based on morphological, biogeographical and ecological differences. The arrangement of P. fuscicollis was revised with two subspecies: the Brown-necked Parrot (P. f. fuscicollis) (which historically occurred in W Africa but is now only common in Gambia) and the Grey-headed Parrot (P. f. suahelicus) (which occurs in low-lying woodland in south-central Africa). Coetzer et al. (2015) supported the proposed divisions from Clancey with genetic evidence for the separations of the Cape Parrot and the two P. fuscicollis subspecies.
A review paper by Perrin (2005) collates and summarises the ecological, behavioural, morphological and molecular data in relation to the taxonomy of the Cape Parrot. The paper also includes colour photos of the species.