Packets of cannabis seeds line the shelves of legal grow shops in Madrid. Many carry labels reporting the percentage of sativa and indica, two types of cannabis. Breeders often label plants that produce a more exciting high as sativa and plants that provide a more mellow feeling as indica, suggesting that cross-breeding tailors that buzz. The conceit is widespread. Botanist Jonathan Page at the University of British Columbia in Vancouver, Canada, says he sees the same at local grow shops.
For reasons that go beyond assessing the quality of the user experience, botanists such as Page are investigating the evolution and present-day diversity of cannabis. To do this, they must confront centuries-old taxonomic questions, including whether cannabis is one species, Cannabis sativa, with several subspecies or varieties, or if it is several distinct species, such as C. sativa, Cannabis indica and Cannabis ruderalis. “It’s complicated taxonomically because of its intimate relationship with humans for long periods of time,” Page says. People have long bred cannabis as a source of fibre, food and oil — as well as for its mind-altering effects (see page S10). As governments relax cannabis laws, commercial growers want more clarity about the chemical properties and capabilities of the herb’s many varieties. In parallel, regulatory bodies trying to establish a legal framework want to be able to classify whether a given type of plant is for fibre (hemp) or recreational or medical use (marijuana).
