MARCHANTIA, in botany, a genus of the order of algae, belonging to the cryptogamia class of plants. There are eight species, of which the most remarkable are, 1. The polymorpha, or great star-handed marchantia, is a native of Britain, growing on the banks of rivulets, on shady moist rocks, the sides of wells, and sometimes bogs. The leaves are about three inches long; from half an inch to an inch broad, lying flat on the ground, and adhering closely to it by numerous downy radicles, which grow out of the middle and base of the leaf on the under side. These leaves are situated on their edges, their upper surface of a dark, shining, green colour, reticulated with numerous, minute, rhomboidal, or lozenge-like scales; variously divided into obtuse lobes, and in the middle by a blackish purple vein; their under side is of a paler green, and their substance coriaceous, and nearly opaque. There are three varieties, from one of which is produced a yellow powder, showing a most curious and wonderful mechanism when examined by the microscope. The leaves have a strong aromatic smell, and acrid taste; and are recommended, in a decoction of skimmed milk, as good in the jaundice and other disorders of the liver. 2. The conica, or conic-mushroom marchantia, with wasted leaves, grows on moist shady banks by the sides of rivulets. The leaves are broad, flat, about two inches long, dichotomous, obtusely lobed, and lie upon one another. Their surface is of a pale-green glossy colour, curiously tessellated with rhomboidal and hexagonal tubercles, each having a white vesicle or wart in the centre, with a puncture on its head. The leaves have a peculiar strong fragrant smell, and acrid aromatic taste. They are supposed to possess the same attenuating quality as the first, but in a higher degree. They are also recommended as an antiscorbutic, and for thinning the blood.