Around this time of year we start to see a lot of poinsettias. The plant is native to western Mexico and Guatemala. For the Aztecs the poinsettia (which they called cuetlaxochitl) was a symbol of purity (rather like the lotus in East Asia). I expect the red color would suggest blood to most ancient Mesoamerican cultures. A reddish-purple dye was made from the plant’s bracts, and its sap was used to treat fevers.
The plant is named for Joel Roberts Poinsett, U.S. ambassador to Mexico from 1825 to 1829. He sent some speciments to Robert Carr at the Bartram Nursery, who introduced the plant into wider cultivation.
LINK: How pointsettias became popular
Image from the U.S. Agricultural Research Service