Roger Wicker, a Mississippi Republican, received a letter containing ricin, a toxin derived from the castor oil plant.

WSJ: Best of the Web Today: Fascism by the Numbers

Plants in this family, which include the rubber tree, castor oil plant and the cassava shrub, are typified by small blossoms, the researchers comment.

BBC: NEWS | Science/Nature | Family found for gigantic flowers

The plants grow wild along highways and in other spots in the U.S. They are also considered ornamental by some gardeners and are cultivated for medicinal castor oil and other products.

WSJ: 'The perfect poison': Ricin used in 3 recent cases