(Business 2.0) – Could tobacco cure cancer? Or alfalfa treat drug addiction? Betting that crops will be the new pharmaceutical factories, biotechnology startups are genetically modifying rice, safflower, and other plants to fight diseases. Many drugs created this way are now headed for clinical trials, and by 2015 the category could be worth an estimated $20.7 billion, according to Kalorama Information.

Plants can produce drugs faster and at a lower cost than traditional manufacturing, argues Elliott L. Fineman, CEO of plant-pharma firm Planet Biotechnology. "You can expand as soon as you get the seeds in the ground." In fact, capital costs for farm-grown drugs are about a quarter of those needed to build a factory, says Andrew Baum, CEO of SemBioSys Genetics. Because safety groups worry that modified seeds might infiltrate traditional fields, companies are using greenhouses and plants that don't cross-pollinate, such as tobacco, to keep seeds contained. Here's a guide to the remedies cropping up.