|photo copyright Frank Tiemann|
The poinsettia's secret is out, so maybe you know already that the red "flowers" are actually modified leaves called bracts. The true flowers are clustered at the the center of these bracts and that's what you're looking at in these beautiful photographs from Flickr.
|photo copyright Martin Heigan|
Poinsettias (Euphorbia pulcherrima) share these very distinctive flowers with all euphorbs (also known as spurges). Unique structures called cyathia hold the flowers. Flowers are either male or female; each cyathium contains both. As the flowers mature, they begin to protrude from the top of the cyathia.
In the center of the photo above you see the fat pomegranate-like ovaries of the female flowers. Male flowers with their anther-topped filaments are more apparent at the extreme right of the photo in the picture below.
|photo copyright Rafael Buono|
Here, ants steal from the glandular nectaries before the plant can appreciate their visit; the anthers are still too immature to dust them with pollen.
The poinsettia was named for Joel Poinsett, a Carolinian who lived in Charleston. He brought the plant from Mexico (where it is native) to the US, in the 1800s.
The poinsettia has been determined to be not poisonous! The Poinsettia Pages by The University of Illinois Extension will fill you in on the facts about that, and all sorts of interesting and useful facts about the poinsettia.
"About the genus Euphorbia" is an excellent article (with beautiful diagrams).