Like any hot and relatively new sector, the cannabis industry can be confusing, with high potential for scams, as the Securities and Exchange Commission has warned, so investors need to know the basics. To start with, there are a handful of large companies that actually touch the marijuana plant — an important distinction — and there are metrics that are unique to the industry that can help investors understand the underlying business. There are six large public cannabis companies that demand attention: Aphria Inc.APHQF, -4.04% APH, -3.97% , Aurora Cannabis Inc. ACBFF, -3.94% ACB, -2.85% , Cronos Group Inc. CRON, -3.59% CRON, -3.42% , Canopy Growth Corp. CGC, -7.57% WEED, -6.96% , GW Pharmaceuticals PLC GWPH, +1.55% and Tilray Inc.TLRY, -5.23% TLRY, -5.23% . Five are Canadian and trade on the Toronto Stock Exchange and on U.S. exchanges or on the over-the-counter market, while one is U.K.-based. All produce thousands of kilograms of weed each quarter, which is critical, as there are dozens of smaller businesses both public and private that have yet to bring products to market. Some of those are expected to die, and some are expected to thrive.