Backyard Field Guide: Pinpointing the Poinsettia

Getting ready for our neighborhood holiday party we've bought a few of the usual poinsettia and out of pure curiosity this morning I thought: what's the story of these plants? if they grow wild, where?

I've only found bits and pieces of information but from what I understand the plant is native to the Pacific coast of Mexico. The ancient Aztecs thought the flower a symbol of purity, a belief which was then adopted (appropriated?) by the first Christian colonists. The above image was taken in the Chihuahua desert and can be found on a local Texas desert site. Looking at it and comparing it to the common greenhouse ones we have here, I can't get over the elegant shape of the wild one's bracts (top leaves, not flower petals as is commonly thought).

Speaking of the borderlands, ecology and religious interpretations: Last night I finished the new Ana Castillo novel The Guardians and highly recommend it.