Nonvascular Plants

Forest floors, streambeds, and cracks in the sidewalk: what commonality do these places share? Often, you will see mosses growing, barely an inch tall, out of these different environments, covering the earth in a shade of green. Mosses, liverworts, and hornworts are all examples of the group of land plants known as nonvascular plants (Fig. 1), which lack vascular systems but have other adaptations for living on land. Keep reading to learn more about Nonvascular Plants, their life cycle, characteristics, and more.

Nonvascular Plants Nonvascular Plants

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Table of contents

    What Is a Nonvascular Plant?

    Land (vascular and nonvascular) plants share one common feature, which plant biologists believed was essential for surviving on land. That characteristic is that their embryos contain tissues from the mother plant to prevent desiccation (drying out). There isn't an abundance of water on land to protect growing plants from drying out, meaning the development of this tissue was essential for survival on land. Both nonvascular plants and vascular plants share this trait.

    Nonvascular plants, Photograph of a liverwort, StudySmarter

    Figure 1. Photograph of a liverwort.

    The Definition of Nonvascular Plants

    Nonvascular plants are a group of early land plants defined by their lack of a vascular system.

    The nonvascular plants are the mosses, liverworts, and hornworts. They also have other characteristics which have helped them survive on land.

    Characteristics of Nonvascular Plants

    Despite not having a vascular system, nonvascular plants still have many important features that have allowed them to succeed on land. Life on land means nonvascular plants need mechanisms to prevent drying out, find water and nutrients and have structures that provide support.

    Preventing Desiccation

    To prevent desiccation or drying out, plants have evolved stomata. Stomata are special openings that allow gas exchange between the plant and its environment. They are controlled by guard cells that will open to let CO2 in for photosynthesis and expel oxygen as a byproduct of photosynthesis. The mosses and hornworts have stomata, but the liverworts do not.

    Another way to prevent drying out is by having a cuticle or a waxy covering. Some species of nonvascular plants have thin cuticles to help prevent drying out, while others do not. Still, their cuticles are quite thin, meaning it is important for nonvascular plants to live in moist environments.

    Finding Water and Nutrients

    Although nonvascular plants lack true leaves, stems, and roots, they still have a dominant haploid gametophyte that can photosynthesize. These gametophytes are often leaf-like. The diploid sporophyte relies on the gametophyte for nutrients and is not free-living (Fig. 2).

    Nonvascular plants Moss Gametophyte and Sporophyte StudySmarterFigure 2. Moss gametophyte (haploid) and sporophyte (diploid) generations.

    Nonvascular plants have root-like structures called rhizoids that help with water absorption. Water can be absorbed through the leaf-like and stem-like structures in the plant, and nonvascular plants often live in water-rich environments. They rely on osmosis to absorb water through their cells to transport water from cell to cell. Osmosis is the movement of water from areas of low solute concentrations to areas of higher solute concentrations.

    The root-like structures, rhizoids, absorb water and provide support for the plant. The cell walls of these plants contain cellulose, which helps provide structure outside of a watery, buoyant environment.

    The Life Cycle of Nonvascular Plants

    One quality of all land plants is the life cycle mechanism known as the alternation of generations. In the alternation of a generation's life cycle, a plant goes through both a multicellular diploid stage (sporophyte) and a multicellular haploid stage (gametophyte). The life cycle of the nonvascular plants follows this basic structure. More detail is provided for each step below (Fig. 3).

    Nonvascular Plants Life Cycle StudySmarterFigure 3. This diagram shows the life cycle of moss.

    1. The diploid multicellular plant, called a sporophyte, will produce spores via meiosis in a sporangium structure. These spores are haploid and unicellular.

    2. The spores will be released and grow into a haploid plant called a gametophyte. The gametophyte is multicellular and has chloroplasts for photosynthesis.

    1. The gametophytes of nonvascular plants have sex organs called gametangia. On the gametangia are archegonium- the female sex organs that make eggs- and antheridium- the male sex organs that make sperm. Eggs and sperm are made via mitosis.

    2. When the sperm are released, they must swim to the egg. Nonvascular plants rely on water for fertilization.

    3. Once the sperm reaches the egg, the diploid sporophyte plant will grow out of the archegonium. This diploid plant relies on the gametophyte for nutrients and is NOT independent.

    4. The cycle restarts when the sporophytes produce spores via meiosis and releases them to grow into new gametophytes.

    Reproduction of Nonvascular Plants

    As discussed above, in the life cycle of a moss, the sexual reproduction of nonvascular plants has a few key features. First, the production of gametes happens in the gametophyte, meaning that they are produced via meiosis, NOT mitosis. The male sex organ is the antheridium and produces sperm or male gametes. The archegonium is the female sex organ that contains the egg, or the female gamete.

    That sperm must swim to the egg and thus requires water or a damp environment to complete fertilization. This requirement is important because it limits the environments that nonvascular plants can live in.

    The fertilized egg will grow into a sporophyte that makes haploid spores via meiosis. The production of the gametophyte from spores is a method of asexual reproduction. That means that the alternation of a generation's life cycle of nonvascular plants includes sexual and asexual reproduction at the different stages.

    Some nonvascular plants may also reproduce asexually in the gametophyte stage. Gametophytes produce " gemma " buds that can fall off and become new plants.

    Nonvascular vs Vascular Plants

    Let's take a look at some of the similarities and differences between nonvascular and vascular plants.

    Similarities

    Nonvascular and vascular plants, although sharing many differences, also share many commonalities. Both nonvascular and vascular plants have:

    • Embryo protection: a way to protect their embryo from drying out using maternal tissue.
    • Alternations of generations: a diploid and haploid stage in their life cycle.

    • Stomata: Besides the liverworts, both nonvascular and vascular plants have these openings to allow for gas exchange.

    • Relationships with fungi: Mutualistic relationships with fungi have allowed both groups of plants to access nutrients more readily.

    • Cuticles: Although more developed in vascular plants, cuticles protect from drying out.

    Differences

    See the table below comparing nonvascular and vascular plant differences (Table 1).

    Nonvascular plantsVascular plants
    DO NOT have vascular systems. Rely on moist environments and diffusion of water. Have well-developed vascular systems for water and nutrient transport.
    Do not have true roots, shoots, or leaves. Have root-like structures, rhizoids, and leaf-like and stem-like structures. Have true roots, shoots, and leaves because of the presence of the vascular system.
    The dominant generation is the haploid gametophyte. They rely on water to reproduce.The dominant generation is the diploid sporophyte. They have many different reproduction strategies, not relying on water.
    They are often small because of a lack of a vascular system.They can grow large and tall because of a vascular system.
    Include the mosses, hornworts, and liverworts. They make up 80% of all plant species. Include the non-seed vascular plants (ferns), the flowering plant, and the gymnosperms (conifers, ginkgos, etc.).

    Table 1: Differences between nonvascular and vascular land plants.

    The Importance of Nonvascular Plants

    Although nonvascular plants like mosses, liverworts, and hornworts are small and do not have flowers, seeds, or other flashy appendages, they play an important role in our environment.

    Have you ever seen a riverbank covered in mosses? Those mosses are more than just slippery, pillowy residents on that riverbank. They help hold the riverbank together and prevent erosion. Mosses, liverworts, and hornworts, growing in dense mats, also do this in other places like the arctic tundra or tropical rainforests.

    They are also often called "pioneer species" because they will be some of the first plants to colonize an area after a natural disaster or other extinction events. They help make the soil more hospitable for other plant and animal life.

    Nonvascular plants - Key takeaways

    • Nonvascular plants are early land plants that lack a vascular system but have protected embryos (protected with maternal tissue).
    • Nonvascular plants include mosses, hornworts, and liverworts.
    • Nonvascular plants have certain adaptations to help them live on land, including thin cuticles, stomata (except liverworts), relationships with fungi, and root-like structures called rhizoids.
    • The dominant generation of nonvascular plants is the haploid gametophyte. The diploid sporophyte is dependent on the gametophyte.
    • Nonvascular plants reproduce both sexually and asexually. The haploid spores that grow into the gametophyte are made via meiosis. The egg and sperm (that make the sporophyte) are made via mitosis.
    • Nonvascular plants differ from vascular plants because they do not have true roots, leaves, and shoots because they do not have vascular systems.

    References

    1. Figure 1: Liverwort (https://commons.wikimedia.org/wiki/File:Liverwort_-_Flickr_-_treegrow.jpg) by Katja Schulz (https://www.flickr.com/people/86548370@N00) Licensed by CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/deed.en).
    Frequently Asked Questions about Nonvascular Plants

    What is an example of a nonvascular plant? 

    Nonvascular plants are collectively called the "bryophytes". They include three groups of plants: the mosses, the liverworts, and the hornworts.

    Do nonvascular plants have roots? 

    No, nonvascular plants do not have true roots. They do, however, have rhizoids, which are root-like structures that nonvascular plants can use to anchor themselves and absorb water. 

    How do nonvascular plants reproduce?

    Nonvascular plants, like all land plants, go through alternations of generations. This means they have both diploid and haploid phases of their life cycle. They can reproduce both sexually and asexually. 


    In sexual reproduction, the sperm and egg are made via mitosis because they are made from sex organs on the gametophyte, which is haploid. The sperm swims to the egg and the zygote develops within the female sex organ of the gametophyte. The zygote is diploid and will grow into a sporophyte. In nonvascular plants, the sporophyte remains dependent on the gametophyte for its entire life cycle. 


    Once the sporophyte is grown, it will produce spores via meiosis. These spores are haploid and unicellular. The spores will be released and once in s suitable environment, they will grow into haploid gametophytes. The cycle will start again. 


    In asexual reproduction, the gametophytes produce buds called "gemma" (via mitosis) that can break off and become new gametophytes. 

    How do nonvascular plants get water?

    Water can be absorbed through the leaf-like, stem-like, or root-like structures in the plant, and nonvascular plants often live in water-rich environments to prevent drying out. They do not have vascular systems to move water throughout their bodies.

    What is the difference between vascular and nonvascular plants? 

    These are the main differences between vascular and nonvascular plants: 

    1. Nonvascular plants DO NOT have vascular systems, vascular plants do contain vascular systems.
    2. Nonvascular plants DO NOT have true roots, shoots, and leaves because of their lack of a vascular system. Vascular plants have true roots, shoots, and leaves.
    3. Nonvascular plants have a dominant haploid gametophyte generation. Vascular plants have a dominant diploid sporophyte generation.
    4. Nonvascular plants remain small in size and cannot grow tall because they have no vascular system. Vascular plants can grow large and tall.
    5. Nonvascular plants are the mosses, hornworts, and liverworts. Vascular plants make up 80% of all plant species, including flowering plants. 


    Test your knowledge with multiple choice flashcards

    Nonvascular plants are a group of plants including the (pick the correct answer) that live on land and lack vascular systems. 

    Stomata are...

    True or False: Nonvascular plants do not have true roots, shoots, or leaves.

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