Why write a strain review? Help other patients find trustworthy strains and get a sense of how a particular strain might help them. A great way to share information, contribute to collective knowledge and giving back to the cannabis community. Cannabis strains are either pure or hybrid varieties of the plant genus Cannabis, which encompasses the species C. sativa, C. indica and C. ruderalis. Varieties are developed to intensify specific characteristics of the plant, or to differentiate the strain for the purposes of marketing or to make it more effective as a drug. Cannabis Types: The Two Main Strains of Weed Indica and Sativa are the two main strains of cannabis. Most of what is available is some combination or variation of the two. Most of what is available is some combination or variation of the two.