Betula n.

genus of the birches, from Latin betula "birch," from Gaulish betu- "bitumen" (source also of Middle Irish beithe "box tree," Welsh bedwen "birch tree"). According to Pliny, so called because the Gauls extracted tar from birches. Birch tar still is sold as an analgesic and stimulant and made into birch beer by the Pennsylvania Dutch.