Knurl

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: It becomes subject to fire, wood-altering spells, and tree diseases. Dispel magic ends the spell's effects.

[Complete Druid's Handbook]

Druidic

Sphere: Plant
(Alteration)
Level: 4

Range: 5 yards/level of caster
Components: V, S, M
Duration: 1 turn/level of caster
Casting Time: 7
Area of Effect: 1 person
Saving Throw: Negates

Material Components: a small twig (consumed)