This distinctive Hawaiian endemic aquatic moss has a superficial resemblance to Fontinalis, but is not closely related. It is seen here in its native habitat under shallow water on the bed of a flowing stream in a forest opening at about 4,000 feet elevation on Kauai.
Large clumps of the aquatic moss Fontinalis hypnoides were attached to tree roots at the edge of Clear Lake, and partially emergent from the water. They were muddy and hard to photograph in the field, but I floated this piece in a bowl at home and obtained images.