Mushrooms do not contain chlorophyll and most are considered as saprophytes since they obtain their nutrition from metabolizing non living organic matter; i.e. they feed on decaying matter.
Edible mushrooms are a good source of B vitamins – especially niacin and riboflavin, and they are rank the highest among vegetables for protein content. Dried mushrooms have almost as much protein as veal. They are also low in fat and calories.
I also understand that the extracts of mushrooms have medicinal properties that are found to help modulate immune system responses and inhibit tumor growth.