What is the Difference Between Liverworts and Hornworts

The main difference between liverworts and hornworts is that the liverworts contain lobate, green, leaf-like structures whereas the hornworts contain narrow, pipe-like structures. Furthermore, the sporophyte of liverworts is short and small while the sporophyte of hornworts is long and slender. In addition, the liverwort sporophyte does not contain stomata while the sporophyte of hornworts contain stomata.

Liverworts and hornworts are two divisions of bryophytes. They undergo the alteration of generations and consist of a prominent gametophyte stage.

Key Areas Covered

1. What are Liverworts
     – Definition, Characteristics, Reproduction
2. What are Hornworts
     – Definition, Characteristics, Reproduction
3. What are the Similarities Between Liverworts and Hornworts
     – Outline of Common Features
4. What is the Difference Between Liverworts and Hornworts
     – Comparison of Key Differences

Key Terms

Bryophytes, Gametophyte, Hornworts, Leaf-Like Structures, Liverworts, Sporophyte

What are Liverworts

Liverworts are a type of bryophytes that belong to the division Marchantiophyta. More than 7000 species of liverworts live on each type of terrestrial habitat on the earth. The main characteristic feature of liverworts is their lobate, leaf-like structures similar to the lobes of the liver. In addition, liverworts may contain openings that allow the gas exchange. However, these openings do not open or close actively. Therefore, they are not considered as stomata. Since these plants do not contain a cuticle, they keep water on the entire surface of the plant to prevent desiccation.

Figure 1: Liverworts

There are two main types of liverworts based on the structure: leafy or foliose liverworts and thalliod liverworts. The leaf-like structures of the leafy liverworts contain a fine hair cover, giving a woolly-look to the plants. For instance, thalloid liverworts are bigger than leafy liverworts. However, there are only fewer species of thalloid liverworts.

Figure 2: Liverwort – Life cycle

What are Hornworts

Hornworts are another division of bryophytes grouped under the division Anthocerotophyta. Around 100-150 species of hornworts live on the earth. The most significant feature of hornworts is the presence of narrow, pipe-like, leaf-like structures. The plant body of the hornworts is thalloid. Furthermore, its photosynthetic cells contain one or two chloroplasts.

Figure 3: Hornworts

Furthermore, the sporophyte of hornworts contains stomata. In addition, the sporophyte is long and contain horn-like capsules in hornworts. Many hornworts maintain symbiotic relationships with nitrogen-fixing, cyanobacteria.

Figure 4: Hornwort – Life Cycle

The gametophyte of hornworts contains embedded gametangia: archegonia and antheridia. Antheridia produce flagellated sperms that can swim to archegonia to fertilize eggs. The embryo develops into a long, slender sporophyte that produces spores inside the capsule. Pseudoelaters cover the spores, facilitating the propelling of the spores in the environment.

Similarities Between Liverworts and Hornworts

• Liverworts and hornworts are two divisions of bryophytes.
• Both undergo an alteration of generations.
• Also, their prominent stage of life is the haploid gametophyte. Therefore, the diploid sporophyte occurs on top of the gametophyte. Also, the sporophyte of these plants does not produce branches.
• Moreover, these plants are embryophytes but, non-vascular, land plants. That means; they do not contain a true vascular tissue that contains lignin.
• Besides, one of the characteristic features of these plants is their limited size.
• In addition, their plant body does not differentiate into stem, leaves, and root. Therefore, it is a thallus.
• Furthermore, they do not depend on the water and nutrients absorbed by their root-like structures called rhizoids. These rhizoids are unicellular.
• Therefore, they can grow in habitats where other vascular plants cannot grow. However, both types of plants prefer moist habitats.
• Also, both liverworts and hornworts produce enclosed reproductive structures including gametangia and sporangia.
• However, they do not produce flowers or seeds. They reproduce via spores released from capsules.
• Their asexual reproduction occurs via fragmentation of leaves to produce gammae. The gammae can disperse and develop into gemetophytes.

Difference Between Liverworts and Hornworts

Definition

Liverworts refer to small, flowerless, green, plants with leaf-like stems or lobed leaves, occurring in moist habitats while hornworts refer to submerged aquatic plants with narrow forked leaves that become translucent and horny as they age. These definitions explain the main difference between liverworts and hornworts.

Division

Liverworts belong to the division Marchantiophyta while hornworts belong to the division Anthocerotophyta.

Morphological Characters of the Gametophyte (n)

Structure

Liverworts can be either thalloid or foliose while hornworts are thalloid.

Symmetry

Moreover, liverworts show a radial or dorsiventral symmetry while hornworts show dorsiventral symmetry.

Leaf-Like Structures

Another difference between liverworts and hornworts is that liverworts contain lobate leaf-like structures similar to the lobes of the liver while hornworts contain narrow, pipe-like structures.

Oil Bodies

The cells of the liverwort leaf-like structure contain oil bodies while the cells of hornworts do not contain such oil bodies.

Chloroplasts per Cell

In addition, liverworts contain many chloroplasts per cell while hornworts contain a single chloroplast per cell.

Storage of Carbon Dioxide

The chloroplasts of the liverworts do not store carbon dioxide while the chloroplasts of the hornworts can store carbon dioxide.

Protonemata

While liverworts contain reduced protonemata, hornworts do not contain protonemata.

Gametangia

The gametangia of liverworts are superficial while the gametangia of hornworts are immersed.

Morphological Characters of the Sporophyte (2n)

Structure

The sporophyte of liverworts is small and does not contain chlorophyll while the sporophyte of hornworts is large and contain chlorophyll. Hence, this is another difference between liverworts and hornworts.

Growth

The sporophyte of liverworts shows a defined growth while the growth of the sporophyte of hornworts is continuous.

Persistence

Persistence of the sporophyte is also a difference between liverworts and hornworts. the sporophyte of liverworts does not last for a long time while the sporophyte of hornworts lasts for a long time.

Stomata

Liverworts do not contain stomata while hornworts contain stomata.

Seta

Furthermore, liverworts contain seta while hornworts do not contain seta.

Capsule

The capsules of liverworts are small while the capsules of hornworts are elongated.

Maturation of Spores

Another difference between liverworts and hornworts is that liverworts show a simultaneous maturation of spores while hornworts show a gradual maturation.

Dispersion of Spores

Liverworts use elasters, a type of cells that can change their shape depending on the moisture content of the dispersal of spores while hornworts use pseudo-elasters that are single-celled structures.

Collumella (Axis of the Sporophyte)

Whereas liverworts do not contain collumella, hornworts contain collumella. Thus, this is another difference between liverworts and hornworts.

Conclusion

Liverworts contain lobate, leaf-like structures while hornworts contain narrow, leaf-like structures. The prominent life stage of both liverworts and hornworts is the gametophyte. The sporophyte of liverworts does not contain stomata while the sporophyte of the hornworts does. Moreover, the former is a small structure while the latter is long. The main difference between liverworts and hornworts is the morphology of both gametophyte and sporophyte.

Reference:

1. “Bryophytes.” Boundless Biology, Lumen Learning, Available Here

Image Courtesy:

1. “Lunularia cruciata” (Public Domain) via Commons Wikimedia    
2. “Liverwort life cycle” (Public Domain) via Commons Wikimedia    
3. “Hornwort (3144429129)” By Jason Hollinger – HornwortUploaded by Amada44 (CC BY 2.0) via Commons Wikimedia  
4. “Hornwort life cycle” By derivative work: Smith609 (talk)Hornwort_life_cicle_svg_diagram.svg: Mariana Ruiz user:LadyofHats – Hornwort_life_cicle_svg_diagram.svg (CC BY 3.0) via Commons Wikimedia