It's well known that plants can't/don't provide all essential nutrients without supplementing. B12 is a major one amongst others.

Yet the reverse is true.

Sidenote: I wouldn't put much stock in Harvard school of "nutrition". They have massive conflicts of interest with companies like Monsanto and also numerous problems with their methodology like oversimplification of the issues. https://www.forbes.com/sites/trevorbutterworth/2013/05/27/to...