The fungal group Basidiomycota, also known as the club fungi, includes some of the most familiar fungi. Within this group of 16,000 species are the mushrooms, toadstools, shelf fungi, and puffballs. Basidiomycetes play a key role in the environment as a decomposers of plant litter. They are distinguished from other fungi by their production of basidiospores, which are borne outside a club-shaped, spore-producing structure called a basidium. This group is poorly represented in the aquatic environment. There are very few species of freshwater species known and the majority of marine species are free-floating with a couple of lignicolous (found on wood) species.