Hemp and cannabis both belong to the Cannabis sativa genus. In order to understand one of the major differences between hemp and cannabis, you should be aware of the generally accepted (although somewhat limiting) nomenclature used by botanists to distinguish between the two most common varieties of Cannabis sativa.

• Sativas are invigorating. They have tall, thin leaves, grow best in humid climates, and have a slow grow cycle.
• Indicas are sedating. They have short, fat leaves, grow best in mild climates, and have a fast grow cycle.

Cannabis can be a sativa, indica, or a mixture of the two, referred to as a hybrid. Hemp will only be a sativa.

https://www.benzinga.com/markets/cannabis/20/06/16397268/how-is-marijuana-different-from-hemp