Vitamin B2 (riboflavin) is found in a wide variety of plant foods in small amounts, including avocados, mushrooms, almonds, leafy green vegetables, and soybeans (1).
Symptoms of vitamin B2 deficiency are sores outside of the lips and in the corners of the mouth, swollen tongue and mouth cavity, and dermatitis (2).
References
1. Messina V, Mangels AR. Considerations in planning vegan diets: children. J Am Diet Assoc. 2001 Jun;101(6):661-9.
2. Groff J, Gropper S. Advanced Nutrition and Human Metabolism, 3rd ed. Wadsworth: 2000.