poinsettia

The word comes from the obsolete genus name Poinsettia, honoring Joel Roberts Poinsett, a 19th-century US minister to Mexico, formed with the suffix -ia.

The name began as a scientific genus title built directly on a person's surname, and passed into everyday English as the common name for the plant itself.

It's tied to the surname Poinsett — the personal name doing double duty as a plant name, joined by the Latinate suffix -ia.