An aquatic moss that hitchhiked into one of my tanks. It's growing about 1" tall on the surface of an unheated tank with hard water, low light, and liquid fertilizer. It's very buoyant, relatively slow growing, and will cover the entire surface of your tank if you let it. Looks kind of cool, but annoying when feeding fish from the surface.

This auction is for one large handful (~6 square inches) of moss from the top of my tank.

If anyone can ID this species, please comment!