same species, different cultivar

Hemp is cannibis plant containing less than 0.3% THC. Marijuana is cannibis plant with more than 0.3% THC.

It's an imperct categorization. It's like categorizing citrus based on their sugar content, some are sweet, some are sour.  It doesn't address the biological differences. 

In fact hemp and marijuana looks exactly the same, and it can be from the same species. 

https://zhidao.baidu.com/question/936868332702543772.html?qbl=relate_question_1

Hemp growing are legal, but is regulated by license.  Technically as long as the plant has less THC, it's fine.