In Mexican Christmas tradition, the red-and-green plant known as the Christmas Eve flower is the poinsettia.
The plant is native to Mexico and Central America, where it grows as a shrub or small tree. Its botanical name is Euphorbia pulcherrima, and its showy red parts are bracts—modified leaves—rather than true flowers. The small yellow flowers sit at the center of the colored bracts.
Its Christmas association comes from a Mexican legend connected with Christmas Eve worship. According to the story, a child named Pepita gathered weeds as a humble offering for the Christ Child; the plants reportedly blossomed into red poinsettias. The legend helped connect the plant with religious celebration.
The plant was named after Joel Roberts Poinsett, the first United States minister to Mexico, who sent specimens to the United States in the 1820s. In Mexico, it is commonly called flor de Nochebuena, meaning “Christmas Eve flower.”