Minnesota gives qualified status to any group that runs a statewide candidate and gets at least 5%. In the November 2018 election, the Grassroots-Legalize Marijuana Party got 5.73% for Attorney General. And the Legal Marijuana Now Party got 5.29% for Auditor. Therefore, they are both qualified for the next two elections. Thanks to Paul Frankel for this news.
Minnesota law permits parties to change their names, so presumably if the two parties wish to merge, the law on party name changes would allow them to join together into a single party.