There are many different types of kale some are grown to be eaten and others as ornamental kale. Both edible and ornamental varieties have curly leaf edges and do not form a head like other culinary type brassicas.
Kale has high nutritional value having high levels of beta carotene, vitamin K, vitamin C, it is also rich in calcium.
Ornamental varieties are grown for the lovely colouring of creamy white to green and pink to purple.
You can see these planted out as border edging plants in the city gardens of Tokyo - strange at first sight but most ornamental, especially in winter when there's not much else to provide colour.