Which is the aquatic bryophyte?

Concept

Bryophytes are small, non-vascular plants whose life cycle depends on water for fertilisation. Most live on damp land, but a few liverworts have floating or submerged aquatic forms.

Application

Riccia fluitans is a thalloid liverwort commonly known as floating crystalwort. Its narrow, repeatedly branching thallus can float in ponds and other still or slow-moving water, so it matches the aquatic habit asked about.

Contrast

• Marchantia palmata is associated with moist terrestrial substrates; moisture dependence does not make it a free-floating aquatic bryophyte.

• Riccia discolor is a terrestrial Riccia; sharing the genus name does not imply the floating habit.

• Marchantia polymorpha usually grows on damp soil, rocks, or disturbed ground rather than as a floating aquatic thallus.

Therefore, the aquatic bryophyte among the given species is Riccia fluitans.