limoncillo

from The Century Dictionary.

• noun In Porto Eico, any one of several trees of the myrtle family, especially Pimenta racemosa, from the leaves of which is distilled the oil used for making bay-rum.
• noun In the southwestern United States and Mexico, any one of several species of Pectis, especially P. papposa, P. diffusa, and P. uniaristata, small, yellow-flowered composites, with linear glandular-dotted leaves, and a strong odor of lemon. In many localities these plants are used for making beverages and are administered in the form of decoctions as a remedy for fever and ague and for other maladies. Also called lemonweed and romerillo.