What is the common name of poinsettias?

Poinsettia is the common name of the poinsettia (Euphorbia pulcherrima).

Specifically, the common name is a made-up name. It is a combination of the last name "Poinsett" and the suffix "-ia." The name honors Joel Roberts Poinsettia (March 2, 1779 - December 2, 1851). Poinsett introduced the plant into the United States of America. Previously, the plant was known only to the indigenous inhabitants and Spanish-speaking settlers of southwestern Mexico.