Curaleaf Holdings (CURLF), a Massachusetts company that grows, processes and sells cannabis through dispensaries in 18 states, last week bought the Chicago cannabis cultivator and retailer Grassroots for $830 million. That makes Curaleaf the biggest cannabis company globally by sales, with expected annual revenue of about $1 billion. Curaleaf wants to build scale in the United States, where two-thirds of states have legalized cannabis for medical purposes. Meanwhile 11 states and Washington, D.C., permit recreational use and more are expected to do the same.