You may have seen various spirulina supplement labels claiming that the product has a significant amount of vitamin B12. Some science writers even point to algae as a plant source of this nutrient. But the truth is that this statement conveys misinformation.
Spirulina contains a vitamin B12 analogue, which is an inactive form of the vitamin. That means that it doesn't fulfill the usual role of active vitamin B12.
Many vegans are led to believe that they can get their vitamin B12 needs using spirulina (or another algae), so be careful not to fall into this trap!