The monotypic Thectocercus (Ridgway, 1912) genus includes a single Neotropical parakeet: Blue-crowned Parakeet.
The Blue-crowned Parakeet was until 2013 included in the Aratinga genus but recent DNA studies resulted in a split.
The five subspecies are native to Bolivia, Brazil, Argentina, Uruguay, Columbia and Venezuela.
It is a medium size parrot with an overall green plumage; the greater wing coverts are green and the tail is green with red in the inner webs.
The nominate subspecies has a dull blue colour on the forehead, crown, cheaks and ear coverts; the other subspecies has less blue colouration.
Most subspecies have a white eye-ring except the T.a. neumanni, which has an orange eye-ring.