Last week’s puzzler was two different kinds of LICHENS.
In North America alone there are 3,600 different kinds of lichens; worldwide there are more than 20,000 species of lichen!
So what is a lichen? A lichen is a symbiotic partnership of two organisms– a fungus and an alga or a cyanobacteria. The fungus holds water and provides the shape and structure, while the alga makes food from the sunlight. Together they form a lichen and can be found all over the world, from tropical rain forests, to the wilderness of the Arctic to dry deserts. Unlike plants, lichens have no roots, stems or leaves.
Lichens grow super slowly–some only a fraction of a millimeter each year–and are a great indicator of clean air. Because they absorb everything in their environments, including pollution, scientists can learn a lot by studying them. Some lichens are over 4000 years old!
Lichens are used by many animals. In North America, more than 50 species of birds, including hummingbirds and golden plovers, use lichen for their nests. For other animals such as the caribou, spruce grouse, and wild turkey, lichen provides an important source of food. Many insects and spiders resemble lichen so they can hide from predators or some use the lichen to hide in or under.
People have traditionally used lichen too, for dyes, clothing, decoration and even supplementing their diet. 
To read more about lichen, check out this link: