Out of the entire dandelion plant, the leaves are the best part for the bearded dragons to eat.
The big dark green leaves are packed with vitamins and minerals.
This part of the dandelion is an excellent source of vitamins A, C, E, and K. Additionally, the leaves contain folate and small amounts of B vitamins. As for minerals, the leaves have a high amount of essential minerals that includes calcium, magnesium, potassium, and iron.
The dandelion flowers are very soft and easy to chew. Bearded dragons will definitely love them. The flowers are an excellent source of antioxidants and beta carotene.
Even though they may seem great to feed your bearded dragons, you should try to limit the number of flowers to feed them. 
The flowers are very filling and could prevent the reptile from eating other foods.
Just don’t load up on one type of green, as you have a vast variety of different greens to choose from, and they’re all great for your dragon in their way.