Plant Kingdom · Lesson 5 of 9
Liverworts and Mosses
“Marchantia gemmae and reproductive branches, moss protonema, leafy shoots and sporophyte development.”
• Distinguish liverworts and mosses through body form and representative genera. • Explain Marchantia gemma-cup reproduction and sexual reproductive structures. • Trace the two gametophyte stages of a moss and describe its foot, seta and capsule. • Identify structures in labelled illustrations of Marchantia, Funaria and Sphagnum. • Relate each reproductive process to generation and chromosome number.
Two ways to organise a bryophyte body
A liverwort such as Marchantia spreads across damp ground as a flattened green thallus. A moss such as Funaria produces an upright leafy shoot. Both are bryophytes and share a dominant haploid gametophyte, water-dependent sexual fertilisation and an attached diploid sporophyte. Their different shapes, methods of vegetative reproduction and development of the gametophyte give useful clues for identification.
Bryophytes commonly occupy shaded stream banks, moist soil and tree bark. Liverwort thalli may be closely pressed against the substrate, whereas a moss cushion rises above it through many compact shoots. The difference is not simply that one is 'smaller' than the other. It concerns how the body is organised and how reproductive structures are positioned.
Liverworts: thalloid and sometimes leafy forms
Having distinguishable upper (dorsal) and lower (ventral) surfaces, often with different functions or structures.
Marchantia has a relatively flat, dorsiventral thallus with a recognisable upper surface and lower surface bearing rhizoids. Its branching body absorbs light across a broad area while remaining close to a moist substrate. Some liverwort species instead possess a leafy shoot with small leaf-like parts commonly arranged in rows. Thus 'liverwort' does not mean every member is a flat green sheet.
Marchantia may bear raised stalk-like reproductive structures. Male structures, called antheridiophores, carry antheridia; female structures, called archegoniophores, bear archegonia. The distinguishing names identify which reproductive organs occur on the structures. Depending on species, male and female structures can develop on separate gametophytes or in related arrangements.
A specialised male reproductive branch or structure bearing antheridia in Marchantia.
A specialised female reproductive branch or structure bearing archegonia in Marchantia.
Gemma cups: asexual reproduction without fertilisation
A small multicellular vegetative propagule able to grow into a new individual without gamete fusion.
On the dorsal surface of a Marchantia thallus, small cup-like structures called gemma cups contain green multicellular gemmae. Rainwater striking a cup can disperse gemmae from the parent thallus. If a gemma reaches a suitable wet surface, its cells divide and establish a new haploid gametophyte. The process is vegetative and does not require the production or fusion of antherozoids and eggs.
A gemma is not a seed, spore or zygote. It is a multicellular piece of the haploid gametophyte produced by ordinary growth processes. Its ploidy is n, the same as the thallus that formed it. After dispersal, a gemma directly gives rise to a new gametophyte rather than passing through a diploid sporophyte stage.
Liverwort sexual reproduction and sporophyte
Antheridia release motile male gametes, which need liquid water to reach archegonia. Fertilisation forms a diploid zygote that stays within protective maternal tissues and develops into a sporophyte. The liverwort sporophyte is commonly described as having a foot, seta and capsule, although exact morphology differs across species. The foot maintains attachment and nutrient transfer; the seta supports the capsule; and the capsule produces spores through meiosis.
The words 'spore' and 'gemma' describe different propagules. A spore formed by meiosis in the diploid sporophyte is a single haploid reproductive cell. A gemma is a multicellular vegetative fragment formed from the haploid gametophyte. The new gametophyte can develop from either, but the cellular origins and reproductive mechanisms are different.
Mosses: protonema before leafy shoot
An early, generally filamentous haploid stage produced after a moss spore germinates.
A moss spore first develops into a protonema, typically a green branched filament spreading over a damp surface. It can resemble a green alga, but it is a developmental stage of a moss, not an independent algal species. Cells within the protonema photosynthesise and divide, allowing the young gametophyte generation to expand before recognisable leafy shoots emerge.
Buds develop on the secondary protonema, giving rise to upright leafy gametophytes. In Funaria and related mosses, these shoots possess a slender axis with small leaf-like parts arranged around it. Multicellular rhizoids attach the plant to the substrate. The leafy shoot is still haploid, despite its more elaborate appearance.
The moss reproductive apparatus
Mature leafy moss gametophytes produce antheridia and archegonia near the tops of reproductive shoots. Water enables antherozoids to move to archegonia. After fertilisation, a diploid sporophyte develops. In a typical Funaria-like structure, the foot transfers resources from the gametophyte, a seta raises the capsule and the capsule contains developing spores.
The moss sporophyte may be greener and more structurally elaborate than that of many liverworts, but it remains attached to and nutritionally supported by the gametophyte. Raising a capsule improves spore release to moving air; fine details of capsule opening and dispersal vary between moss taxa. Spores formed by meiosis are haploid and germinate to begin the protonemal stage.
| Character | Marchantia liverwort | Funaria moss |
|---|---|---|
| Main gametophyte | Flattened dorsiventral thallus | Leafy upright shoot after protonema |
| Vegetative propagation | Fragmentation and gemma cups | Fragmentation, budding in protonema |
| Rhizoids | On underside of thallus | Multicellular, commonly branched |
| Sex organs | Often on specialised reproductive branches | Often at apex of leafy shoots |
| Sporophyte | Foot, seta, capsule (form varies) | Foot, elongated seta, capsule |
| Distinctive visible clue | Gemma cups; antheridiophore/archegoniophore | Protonema and leafy gametophyte |
Sphagnum and its ability to retain water
Sphagnum forms dense growth in wet habitats and contains specialised water-retaining tissues in many species. This supports the formation of peat in waterlogged, slowly decomposing environments. The resulting material has been used historically for fuel and packaging because of its capacity to absorb water. Peatlands are also important carbon stores; ecological consequences of drainage or extraction should be considered before treating peat as an unlimited resource.
The textbook figure includes Sphagnum branches and specialised reproductive regions. Some mosses place male and female organs on distinct branches or shoots. These visual details help students recognise that mosses share a general reproductive plan but need not have exactly the same external appearance.
A ploidy checkpoint for difficult comparisons
| Item | Expected ploidy | Reason |
|---|---|---|
| Marchantia thallus cell | n | Part of gametophyte |
| Marchantia gemma cell | n | Vegetative outgrowth of haploid thallus |
| Funaria protonema cell | n | Germinates from a haploid spore |
| Funaria leaf-like cell | n | Part of the leafy gametophyte |
| Zygote and young sporophyte | 2n | Formed after fertilisation |
| Spore mother cell before meiosis | 2n | Part of sporophyte |
| Released spore | n | Product of meiosis |
Chromosome number cannot be inferred simply from whether a cell is large, green, mature or part of a reproductive structure. Ask which generation produced it. A moss leaf-like cell and a gemma are both haploid because they belong to a gametophyte. A sporophyte capsule contains diploid tissues, while the spores produced after meiosis in that capsule are haploid.
Problem
A student sees a green multicellular structure inside a cup on a Marchantia thallus and calls it a spore. How should this be corrected?
- 1.A gemma cup holds multicellular gemmae formed from the haploid gametophyte.
- 2.Gemmae disperse and develop without gamete fusion or meiosis; they are vegetative propagules.
- 3.Spores are formed by meiosis within the diploid sporophyte's capsule and are generally single cells when released.
Quick Quiz
Quiz
What is the usual major body form of Marchantia?
What is a gemma?
What develops directly from a germinating moss spore?
Which structure generally raises the moss capsule?
A Marchantia gemma cell belongs to which chromosome phase?
Where are moss spores formed?
Practice Problems
- Compare the body organisation of Marchantia and Funaria, including reproductive structures.
- Trace how one Marchantia gemma can establish a new individual.
- Describe protonema formation and its role in moss development.
- Label a moss sporophyte and explain the function of foot, seta and capsule.
- Explain why a gemma cell, protonema cell and leafy shoot cell are all haploid but a capsule wall cell is diploid.
Marchantia has a dorsiventral thallus with rhizoids and gemma cups; its specialised reproductive branches can carry sex organs. Funaria has a protonema followed by a leafy gametophyte; a diploid foot-seta-capsule sporophyte remains attached.
Key Takeaways
Marchantia is a liverwort with a dorsiventral thallus, rhizoids, gemma cups and sometimes specialised male and female reproductive branches. Gemmae are multicellular haploid vegetative propagules, not spores or zygotes. A moss spore germinates into a protonema; buds develop into a leafy haploid gametophyte. After fertilisation, the attached diploid sporophyte develops a foot, seta and spore-producing capsule. Funaria and Sphagnum are important moss examples; Sphagnum can retain water and contribute to peat formation.