Explanation

Vitamin-$B_{12}$is not found in plants. However, it is considered that $Spirulina$ (an algae) contain$\ B_{12}$. Vitamin-$B_{12}$ is synthesized by intestinal bacteria, which in fact are main source of vitamin-$B_{12}$. Many micro-organisms (bacteria) of the stomach of ruminant mammals also synthesize large quantities of vitamin-$B_{12}$.