Mullein leaves (Verbascum thapsus) is often mentioned as containing B12. Fine. MAybe it does, and maybe the ratio between bioavailable, active B12 and inactive B12 analogues is terrific.

But - why don't the sites that mention mullein list threir sources? If they hae seen reliable information about this, it should also, ideally, contain information about how much B12 mullein contains, and if the studies include information about the inactive/inactive B12 ratio.