Rhubarb

Latin name: Rheum sp.
Plant Family:  Buckwheat (Polygonaceae)
Lifespan: Perennial
Origin: Originally from China but cultivated all over the world.
Growing: This plant is resilient and can grow just about anywhere. It prefers full sun but will tolerate light shade.
Edibility: While the leaves are toxic, the stalks are one of the most popularly used perennial vegetables in the west. Mainly know for pies. The flowers are also edible and are similar to cauliflower. 
Medicinal uses: It's a purgative and used to treat constipation. 
Permaculture Uses: It's a dynamic accumulator of nutrients and a great mulch crop due to it's large leaves. The large leaves are also a great ingredient for the compost.
Price: $5 per plant