Marchantiopsida

Marchantiopsida is a class of liverworts within the division Marchantiophyta, commonly referred to as complex thalloid liverworts. Members of this class have dorsiventral, flattened thalli that are more morphologically elaborate than those of simpler liverworts. They are non-vascular bryophytes that rely on diffusion for most internal transport.

Anatomically, Marchantiopsida thalli typically show a thallus with internal air chambers and a photosynthetic upper surface, a ventral region with rhizoids, and often a central midrib. Many species contain oil bodies within their cells. The thallus can bear structures for vegetative propagation, such as gemma cups, which produce gemmae for asexual reproduction.

Reproduction in Marchantiopsida includes both sexual and asexual modes. Sexual reproduction is oogamous: female thalli bear archegonia on archegoniophores and male thalli bear antheridia on antheridiophores, with fertilization requiring water. The resulting sporophyte grows from the archegonium and remains attached to the gametophyte, producing a sporangium that dispenses spores, often with elaters to aid dispersal. Asexual reproduction is common as well, particularly through gemmae produced in gemma cups on the thallus.

Habitat and ecology: These liverworts favor moist, shaded environments and are commonly found on damp soil, rocks, decaying wood, and other substrates in tropical and temperate regions worldwide.

Taxonomy and significance: Marchantiopsida encompasses the more complex, thallose liverworts, with Marchantia as a well-known representative. The model species Marchantia polymorpha has been extensively used to study development, physiology, and evolution in land plants.