This realistic-looking Poinsettia is about 2 3/4 inches across when crocheted in No. 10 crochet cotton with a US 4/2mm hook

You’ll need buttons, beads or other embellishment for the center of the flower.

The Lion Brand website listed here includes a very thorough and helpful photo-tutorial for the Poinsettia that was originally printed in Crochet Garden.

Here are instructions for turning the Poinsettia (and any other crochet motif) into an ornament: http://www.textilefusion.com/bookblog/?p=1031