Lesson 6 of 12 · 6 min
Liverworts and mosses
NCERT §3.2.1–3.2.2
Beside a stream the club finds a different green: flat, lobed sheets pressed to the wet bank, dotted with tiny cups holding green specks. The guide calls it a liverwort and lets them compare it with the upright moss on the boulder.
The lesson in notes
In short
Liverworts grow in moist, shady spots: stream banks, marshy ground, damp soil, tree bark and deep in woods.
A thalloid liverwort such as Marchantia has a dorsiventral thallus pressed flat against the ground. Leafy liverworts carry tiny leaf-like appendages in two rows on stem-like parts.
Liverworts reproduce asexually by fragmentation of the thallus, or by gemmae (singular gemma): green, multicellular asexual buds formed in small cups, the gemma cups, on the thallus. Gemmae break off and grow into new plants.
Male and female sex organs may be on one thallus or on separate thalli. The sporophyte has a foot, a seta and a capsule; spores form in the capsule after meiosis and grow into free-living gametophytes.
In mosses the gametophyte is the main stage, and it has two parts. The protonema grows straight from a spore and is creeping, green, branched and often filamentous.
The leafy stage grows as a lateral bud from the secondary protonema. It has upright, slender axes with spirally arranged leaves, held in the soil by multicellular, branched rhizoids, and it carries the sex organs.
Mosses reproduce vegetatively by fragmentation and by budding in the secondary protonema. Antheridia and archegonia form at the tips of the leafy shoots.
After fertilisation the zygote forms a sporophyte of foot, seta and capsule, more elaborate than a liverwort's. Spores form in the capsule after meiosis, and mosses have an elaborate way of dispersing them. Examples: Funaria, Polytrichum, Sphagnum.