Black bryony is out only native relative of the yam family; white bryony is a similar plant but belongs to a totally different family of plants.
Black bryony because the leaves are a very dark, glossy green which can look almost black in poor, shaded light. Once the leaves are seen then there should be no mistaking this plant and the leaves are far more striking than the small, rather insignificant green flowers. In autumn though these flowers turn in to strings of bright red berries.
Here is an interesting note I discovered in a book somewhere. Black bryony entwines clockwise whereas white bryony entwines anti-clockwise. Not a lot of people know that!