Exuberant in growth; rank; excessive; very abundant; as, a luxuriant growth of grass; luxuriant foliage
Luxuriant plants, trees, and gardens are large, healthy, and growing well. There were two very large oak trees in front of our house with wide spreading branches and luxuriant foliage
If you describe someone's hair as luxuriant, you mean that it is very thick and healthy. Hair that's thick and luxuriant needs regular trimming