Some green walnuts in tree. Walnuts are rounded, single-seeded stone fruits of the walnut tree. The walnut fruit is enclosed in a green, leathery, fleshy husk. This husk is inedible. After harvest, the removal of the husk reveals the wrinkly walnut shell, which is in two halves. This shell is hard and encloses the kernel, which is also made up of two halves separated by a partition. The seed kernels — commonly available as shelled walnuts — are enclosed in a brown seed coat which contains antioxidants.