[1] This genus includes roughly 90 to 110 species, and is found in North America, Europe, and Asia.

As a result, identification to the species can be challenging, and knowledge of the host plant can be valuable.

Parasitoids such as Lysiphlebus salicaphis and Aphelinus aureus are known to specialize in this genus.

As they feed on phloem sap, the aphids excrete honeydew, which is in turn consumed by ants.

Some members of this genus (C. populialbae and C. populeti) have been shown to vary the nutritional content of their honeydew depending on the presence of attending ants; however this has been shown to not be universal to the genus.