There's only Cannabis sativa and Cannabis indica. While Cannabis ruderalis may be considered to be a sub-species of Cannabis sativa, it's more than likely that Cannabis ruderalis is in a species of it's own. When identifying strains, it's widely popular belief that pure Cannabis sativa strains are tall and laxly branched with relatively narrow leaflets, while pure Cannabis indica is shorter, conical in shape, and has relatively wide leaflets. Pure Cannabis ruderalis strains, while staying as short as most Cannabis indica strains, differ somewhat from it's two cousins only in one way; they don't branch -- meaning, they only produce one, long vertical growth mass. Supposedly most ruderalis strains are auto-flowering. Whether this is true or not hasn't been physically documented by me, so don't take my word for it.