Casting a knurl spell transforms a creature's arm into a tree branch of the same thickness, covered with bark and twigs. The new limb possesses neither elbow nor wrist joints – not even a hand. The “arm” remains attached to the shoulder. The spell's recipient can use it as a club but not to manipulate tools, weapons, or spell components.
The caster chooses which of the recipient's arms to affect. A character could use multiple knurl spells to transform both arms of a humanoid. The arm is treated for all purposes as a tree branch, becoming subject to fire, wood-altering spells, and tree diseases. A successful dispel magic spell ends the effect.
The material component is a small twig.
Notes: Uncommon for druids; optionally available to other nature priests.