Liverworts - Characteristics and Life Cycle

Table of Contents:

• Bryophytes
• What are Liverworts?
• Classification
• Characteristic Features of Liverworts
• Liverworts – Life Cycle
• Frequently Asked Questions

Bryophytes

Bryophytes are amphibians within the plant kingdom. They face harsh and diverse environmental conditions that also give opportunities for them to diversify. There are approximately 18000 to 23000 extant species of bryophytes. The three widely accepted groups of bryophytes are –

• Mosses
• Liverworts
• Hornworts

These groups share common ancestors and also a number of biological and ecological traits.

What are Liverworts?

Liverworts are a diversified group of small, terrestrial, herbaceous plants, that approximately comprise about 9000 species. They are usually less than 10 cm in length. They most occupy a variety of habitats, like the soil along river banks, trails, rocks, trees, etc. They are found worldwide and are especially concentrated in the southern rainforests.

Let’s look at the classification, life cycle and various characteristic features pertaining to this division of plants.

Classification

Internal Classification

The liverworts are subdivided into –

• Marchantioid group or complex thalloids
• Jungermannioid group with simple thalloids (Metzgeriales) and leafy liverworts (Jungermaniales)
• There is a diverging lineage leading to a third class called Haplomitriopsida.

Characteristic Features of Liverworts

• The plant body of a liverwort is called a thalloid, which is dorsoventral in nature.
• The leaves of liverworts are arranged in rows (typically three rows) and tend to appear flattened. Both their thalloid and leafy forms often have an endosymbiotic relationship with fungi.
• The leaves are commonly lobed or divided. Sometimes, the lobe margins can also be toothed or ciliated.
• Rhizoids are thin-walled, unicellular, and usually hyaline.
• They are distinguished from other embryophytes by the presence of oil bodies, a unique membrane-bound organelle.
• The sporophyte setae of liverworts are parenchymatous. These parenchymatous cells elongate by expansion instead of cell division.
• Their capsules lack cuticles, columella and stomates that are usually common in hornworts and mosses.

Liverworts – Life Cycle

Liverworts can be monoicous or dioicous. Also, they show both sexual and asexual reproduction.

Asexual Reproduction

In liverworts, asexual reproduction takes place by fragmentation of the thallus, or by the generation of special structures called gemmae. These gemmae are multicellular, green, asexual buds that develop in the gemma cups, which are small receptacles present on the plant body or thallus. These structures become disconnected from the parent plant body and then germinate into new individuals.

Sexual Reproduction

Spore Germination – Typically, spore germination is initiated with swelling and division of the spore to form a multicellular protonema. The protonema is a highly branched thread-like structure in mosses, whereas it is reduced as cells in most hornworts and liverworts. The protonema develops into a mature gamete-bearing plant.

In sexual reproduction, the female and male sex organs are produced either on the same or different thalli. Here, the sporophyte is evolved into seta, capsule and foot. Usually the spores are produced inside the capsule, after meiosis. These spores germinate to form a free-living gametophyte.

Like hornworts and mosses, they have a heteromorphic life cycle with a sporophyte that is comparatively short-lived and nutritionally dependent on the free-living gametophyte.

Also Explore: NEET MCQs on Bryophyta

Further Reading: Difference between Liverworts and Mosses

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