Brambles

A nonmagical wooden bludgeoning weapon you hold (such as a club, quarterstaff, greatclub, or boomerang) grows long, sharp spines like a hawthorn or locust tree.

While the spell lasts, the weapon becomes magical and deals 2d4 additional piercing damage on a hit. This spell ends if the weapon is no longer in your possession at the end of your turn, or if you cast it again.

Adapted from Complete Divine (3e).