Lichens are those flat patches of green and yellow growing on rocks, boulders, and tree bark. Lichens are actually two different organisms (fungus and algae), both working together and living as one. The algae provide food for itself and the fungus through photosynthesis. The fungus provides protection for the algae. Lichens have been used for dyes, perfumes and in healing. Researchers have discovered beneficial chemicals in lichens with antibacterial, antiviral, compounds and can be processed into natural herbicides. Some lichens are poisonous and have been used on arrow tips to kill animals.