In Mexico the flower’s true name is Flor de Nochebuena, or Christmas Eve Flower. It is native to Mexico and had been used by the ancient Aztecs for medicine and red dye. Today in Mexico, as in the US and UK, it is a symbol of Christmas.
The Christmas Eve flower was introduced to the USA in 1825 by Joel Roberts Poinsett, and of course it was decided to rename the flower after Poinsett, as if he had discovered the flower. Because nothing ever exists until white people know about it.
As if that weren’t bad enough, Poinsett wasn’t exactly beloved by Mexicans. He served as the first US Minister to Mexico. His primary job was to convince Mexico to give now-Texas to the US government. But in the midst of the political turmoil of Mexico’s early Republic, Poinsett stepped outside the bounds of his role as minister and began meddling in Mexican politics. Eventually he got involved in some very suspicious presidential election circumstances that lead to his recall as Minister in 1829. At that point, even the people he supported wanted him out of there.