Question

Compare liverworts. hornworts, and mosses in terms of their vegetative and reproductive morphologies.

Answer 1

Liverworts have thallose gametophytes but most are leafy. The leaves are arranged in two or three rows. Sex organs are present on
the surface and are protected by enveloping structures. The
rhizoids are unicellular. Leaves are usually lobed and without
a midrib. The whole leaf is one cell thick. The sporangium matures while still protected by enveloping structures. At maturity the
colourless seta pushes it and it comes out of the protective sheath. The seta remains erect due to water pressure within its cells. Spores
are shed when sporangium ruptures. It ruptures along the
four longitudinal lines due to which the spores and elaters are exposed to air. The elaters uncoil and the spores are dispersed.

The hornworts also possess a thallose gametophyte and the sex organs are entirely embedded in the thallus. The sporophyte is horn-shaped and consists of a sporangium. The sporangium matures from the apex downward to its foot. The spores are usually shed from the apex while growth above the foot continues. Due to this continued growth, it produces new spores as long as the favourable conditions are present.

The gametophyte in mosses is leafy and leaves are present in more than three rows. Sex organs are generally
protected by sheathing leaves. Rhizoids are multicellular
and profusely branched. Leaves are not lobed and possess a midrib which is several cells in thickness. The sporangium
is produced after seta elongates; the
seta is photosynthetic and rigid with thick-walled cells. Seta has a conducting system to transfer water and minerals to the developing sporophyte. The sporangium in mosses possess a lid at maturity to control spore dispersal.