lichen
dr. dolittle | December 21, 2013
Unlike Santa's reindeer living in the lap of luxury at the North Pole, wild reindeer that live in the barren tundra have to find their own food. Being too chilly for trees, the tundra is hospitable to only shrubs, grasses and lichen, which are abundant during the warmer seasons. However, during the winter when the grasses and shrubs are scarce reindeer survive off lichen, comprised mainly of quick-energy in the form of carbohydrates. In fact, they reportedly eat about 4-11 pounds of lichen each day.
Source:
Animal Planet