birch (n.)

"hardy, slender northern forest tree noted for its white bark," Old English berc, beorc (also the name of the rune for "b"), from Proto-Germanic *berkjon (source also of Old Saxon birka, Old Norse börk, Danish birk, Swedish and Icelandic björk (which is also a girl's given name), Middle Dutch berke, Dutch berk, Old High German birihha, German Birke).

This is from PIE *bhergo (source also of Ossetian barz, Old Church Slavonic breza, Russian bereza, Lithuanian beržas, Sanskrit bhurjah, all names of birch-like trees, Latin fraxinus "mountain ash"), from root *bhereg- "to shine; bright, white," in reference to the bark. Birch beer is by 1827, American English.

"to flog," 1830, from the noun in the sense "bunch of birch twigs used for flogging" (1640s); see birch (n.). Related: Birched; birching.