who introduced the poinsettia to the united states
Joel Roberts Poinsett
Poinsettia
 It derives its common English name from Joel Roberts Poinsett, the first United States Minister to Mexico, who is credited with introducing the plant to the US in the 1820s. 
wiki:1120798
Poinsettia [SEP] Introduction
The poinsettia ( or ) ("Euphorbia pulcherrima") is a commercially important plant species of the diverse spurge family (Euphorbiaceae). Indigenous to Central America, it was described as a new species in 1834. It is particularly well known for its red and green foliage and is widely used in Christmas floral displays. It derives its common English name from Joel Roberts Poinsett, the first United States Minister to Mexico, who is credited with introducing the plant to the US in the 1820s. Poinsettias are shrubs or small trees, with heights of . Though often stated to be highly toxic, the poinsettia is not dangerous to pets or children.