Marchantia polymorpha (Common liverwort)
Species: M. polymorpha
Binomial name: Marchantia polymorpha
Synonyms: Marchantia alpestris, Marchantia aquatica
Common names: Common liverwort, Umbrella liverwort
Marchantia polymorpha is a large liverwort and it is found worldwide from tropical to arctic climates. It grows on moist soil and rocks in damp habitats such as the banks of streams and pools, bogs, fens and dune slacks. It rapidly colonizes burnt ground after fires. It often grows in man-made habitats such as gardens, paths and greenhouses and can be a horticultural weed. It is variable in appearance and has several subspecies. It is dioecious, dense, fleshy mat that grows prostrate over the surface. It has separate male and female plants. It is a thallose liverwort which forms a rosette of flattened thalli with forked branches. The thalli (leaf-like structure) grow up to 10 cm long with a width of up to 2 cm. It is usually green in colour but older plants can become brown or purplish. The upper surface has a pattern of hexagonal markings. The underside is covered by many root-like rhizoids which attach the plant to the soil. The plants produce umbrella-like reproductive structures known as gametophores. The gametophores of female plants consist of a stalk with star-like rays at the top. These contain archegonia, the organs which produce the ova. Male gametophores are topped by a flattened disc containing the antheridia which produce sperm.
Marchantia polymorpha can reproduce both sexually and asexually. Sexual reproduction involves sperm from the male plant fertilizing ova from the female plants. A fertilized ovum develops into a small sporophyte plant which remains attached to the larger gametophyte plant. The sporophyte produces male and female spores which develop into free-living gametophyte plants.
Asexual reproduction can occur when older parts of the plant die and newer branches develop into separate plants. It can also occur by means of gemmae, balls of cells which are genetically identical to the parent and contained in cup-like structures on the upper surface of the plant. These are dispersed when rain splashes the cups and develop into new plants.
Marchantia polymorpha has a dual life-cycle with one generation producing male and female parts, and the next generation producing spores in gemmae cups. See photos below.
Marchantia polymorpha rosette of flattened thalli with forked branches. The round discs on the thalli are gemmae cups that hold the asexual stage. Rain drops disperse them.