Left tree radical, four strokes for trunk, branches, and roots. It indexes
杖 in the wood-objects family:
板 plank,
枝 branch,
桥 bridge,
杆 pole,
棍 cudgel. A
杖 is a wooden staff — walking stick, monk's staff, executioner's rod — so the radical does the literal semantic work: this is a thing made of wood.
