An order of liverworts of the subclass Marchantiidae, consisting of a single genus (Monoclea). The gametophyte is among the largest of all liverworts; its thallus consists of homogeneous cells except for scattered oil cells. The rhizoids are smooth and both thick-walled and thin-walled. The sex organs are grouped but not elevated: the antheridia are sunken in cavities and grouped into receptacles, while the archegonia are enclosed in groups by involucres. The very long, massive seta considerably elevates the capsules which dehisce spoonlike by one slit. The lobing of spore mother cells is unique in the subclass Marchantiidae.