Scientifically (and legally), all cannabis plants are considered to be Cannabis sativa L..
In practice, Indica and Sativa are broad categories used to indicate a particular strain’s place in the the ‘spectrum’ of cannabis. There are a multitude of different growth-patterns, qualities and effects within this spectrum and the variations between strains are largely due to the fact that cannabis displays a remarkable ability to adapt to a wide range of different environments.
Since all branches of the cannabis family tree can interbreed freely (including industrial hemp and Cannabis ruderalis J.), some botanists consider all forms of the plant to be members of a single polymorphic species.