I can't tell from the picture what species it is.

Is it Giant (otherwise known as purple moonflower) Morningglory? We have some acres of that one down here. It gets BIG, thus the name. The seed is black and shaped just like other species, but it is big, the size of soybean or pea. The plant has some spines on the vines that look like thorns, but are soft to the touch. It runs about twenty feet or so in all directions, and the base will get to be bigger in diameter than regular types of morningglory.