Heirloom cannabis strains are strains that have existed for many generations. However, this is not the only thing that makes them unique. Heirloom cannabis strains are distinct from other cannabis strains because of the purity which they offer. Unlike most strains of cannabis, heirloom cannabis strains have never been crossbred with any strain, only existing in their pure, natural form.  This unadulterated and unchanged state gives heirloom cannabis its status as a prized strain.