Liverworts are small, simple, non-vascular plants belonging to Bryophyta. They are among the earliest land plants and usually grow in moist, shady places such as damp soil, rocks, tree bark, and near streams. Since they require water for fertilisation, they are called the “amphibians of the plant kingdom.” Around 9,000 species of liverworts are known worldwide, with the greatest diversity found in tropical and temperate rainforests.
Characteristics of Liverworts
- A liverwort's dorsoventral thalloid plant body is referred to as a thalloid.
- Liverworts have flattened leaves that are organised in rows, usually three rows. Because they are leafy and thalloid so frequently coexist endosymbiotically with fungi.
- The leaves are frequently split or lobed. The edges of the lobes can occasionally be serrated or ciliated as well.
- Rhizoids are typically hyaline, unicellular, and have thin walls.
- They differ from the embryophytes because of having oil bodies, a special organelle that is membrane-bound.
- Liverwort sporophyte setae are parenchymatous. Instead of cell division, these parenchymatous cells enlarge.
- The cuticles, columella, and stomata that are typically present in mosses and the Hornwort are absent from their capsules.
Types of Liverwort
The different types of liverworts include:
- Thalloid Liverwort: Group of Marchantioid or complicated thalloid and thallose liverworts.
- Leafy or Scaly Liverworts: they are less common; they almost resemble mosses and small ferns.
Lifecycle of Liverwort
Liverworts show alternation of generations, in which two distinct phases occur in the life cycle: Gametophyte (haploid, n) – Dominant and independent stage and Sporophyte (diploid, 2n) – Dependent on gametophyte.
- Gametophyte Stage (n) – Dominant Phase: The green, flat plant body (thallus) is the gametophyte. It produces sex organs: Antheridia (male organs) → produce sperm and Archegonia (female organs) → produce egg
- In Marchantia, these are borne on special stalks: Antheridiophore and Archegoniophore
- The zygote develops into a sporophyte. The sporophyte remains attached to and dependent on the gametophyte.
- It has three parts: the foot (absorbs nutrients), the seta (stalk), and the capsule (spore-producing structure)
- Inside the capsule, meiosis occurs. Haploid spores (n) are produced. Spores are released and dispersed by wind.
Reproduction of Liverwort
There would be asexual and sexual reproduction.
Asexual Reproduction
- Asexual reproduction occurs in liverworts either by thallus fragmentation or through the development of unique structures known as gemmae.
- These gemmae grow in the gemma cups, which are tiny receptacles found on the plant body or thallus.
- They are green, multicellular and the type of asexual buds. These components separate from the parent plant's body and develop into new individuals.
Sexual Reproduction
- Usually, the enlargement and spore would divide to create a multicellular protonema, marking the beginning of spore germination. While the protonema is reduced to cells in the majority of hornworts and liverworts, it is a highly branching, thread-like structure in mosses.
- The protonema matures into a plant capable of producing gametes.
- The male and female sex organs are generated on either the same or distinct thalli during sexual reproduction. Here, the seta, capsule, and foot evolved from the sporophyte.
- After meiosis, spores are often formed inside the capsule. A free-living gametophyte develops when these spores germinate. Similar to hornworts, liverworts would be a heteromorphic cycle by having a very short-lived sporophyte that relies on the free-living gametophyte for nourishment.