Aphids of the genus Cinara found in Canada east of the Rockies are, with few exceptions, large, dark in colour, and compact in form. They live entirely on coniferous hosts and each species is restricted either to a single species of plant, or to plants of the same genus. Their unvarying choice of a host plant makes it possible to separate the species into groups according to the genus of plant on which they occur; this characteristic is used in the following key.