Lichens
Lichens are composites of two organisms: algae living within fungi. The algae provide the fungi with food through photosynthesis, and the fungi provide the algae with shelter from the elements. Combinations of algal and fungal species are so specific that they are given their own species names as lichens. Due to their small size, accurate identification of lichens can be tricky and may require a hand lens, a microscope, or chemical tests.
