Not a cabbage but an aquatic relative to the sweet potato.  It is thought to have originated in Africa, and is grown and used throughout southeast Asia.  This vegetable has become popular in Australia and In Florida and the Southeast United States.  The long spear shaped leaves connect to cylindrical shapes stems  that are hollow with small dark blossoms.

Select plants with glossy leaves and was carefully as insects are often found in the hollow stems.

With a light delicate flavor, it is used in stir fry and often cooked as you would cook spinach.