why should there be? Cannabis is a vascular plant, specifically a flowering herb. As all angiosperms (flowering plants), they contain cotyledons. So for all angiosperms, when the plant is no longer dependent on cotyledons for nutrient you can consider it on “veg” - and there is your standard for cannabis - i guess.
fyi my understanding of botany is not professional… I like these two books for thee types of questions: