The species was first described in the 1844 Proceedings of the Entomological Society of London, which were published in 1845. A subsequent publication in 1846 misspelled the name, but is not the original spelling.
Some populations near the Pacific coast are entirely black, instead of the bluish coloration that is more widespread. Fujita's illustrated catalog (2010) erroneously treated the synonym P. coerulescens as a valid subspecific name, arbitrarily deciding that the black form deserved recognition from the widespread blue form by considering it to be the nominal subspecies. In fact the holotype of C. oregonensis is blue, and thus P. coerulescens is an obvious synonym. Regardless, such minimal color variations should not be recognized as subspecies.