Most studies of plant domestication have been carried out on food crops. The Christmas poinsettia (Euphorbia pulcherrima) has been used as an ornamental and for ceremonial purposes since pre-Columbian times. Today, the poinsettia is the floral symbol of Christmas and is one of the highest-selling potted plants in the world. This chapter presents work exemplifying this plant as an evolutionary model for ornamental plants. An analysis is presented of its geographic context, with maps of the potential distribution of the species and of the geographical distribution of the genetic variants of both wild and cultivated plants. These, along with their genealogies, allowed the identification of the source of the germplasm of commercial cultivars, supporting the legend that the poinsettias that J. R. Poinsett sent to the USA in 1828 came from Guerrero, Mexico. Nearly 200 years later, allometric relationships and morphological and biomechanical differences between wild and cultivated poinsettias were analyzed. Intense artificial selection did not break the natural relationship between leaf area and stem volume. Compared to wild ancestors, cultivated plants show an increase in branching, shorter internodes, and stems with greater resistance to breakage.