Aquatic moss greatly help improve water quality in an aquarium. Mosses absorb various nutrients like nitrates from the water and can grow in less demanding conditions. They do not need high light or CO2 injection. They help in harbouring a lot of micro-organisms which act as feed for small fish fry and also as a place to escape predation. The more common varieties are Java Moss and Christmas moss. Other more demanding moss include Fissidens sp., Willow moss etc. Among the liverworts, Pellia and Riccia are well known in the hobby.