leather-cup, a genus of the order of algae, belonging to the cryptogamia clasps of plants. Of this genus there is but one species known, which grows naturally on the banks of ditches and rivulets, in a gravelly or sandy soil, both in England and Scotland. It grows flat upon the ground in a circle or patch, composed of numerous thin, green, pellucid leaves, marked with a few whitish veins near the base, divided and subdivided into obtuse segments obscurely crenated on the edges. The margins of the leaves are a little elevated, but the interior parts adhere close to the ground by a fine down, which answers the purpose of roots. The seeds are so small as to be almost imperceptible.