Have you ever noticed little green plants growing in unusual places like forest floors, streambeds, and even sidewalks? These tiny plants, barely an inch tall, are actually a type of land plant called nonvascular plants. Mosses, liverworts, and hornworts are all part of this group of plants (check out Fig. 1). Unlike other plants, they don't have vascular systems. But don't let that fool you—they have other cool ways of living on land.
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 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.
Nonvascular plants have managed to survive on land even without a vascular system because they have developed some important features. In order to prevent drying out, they have evolved stomata, which are special openings that let gases in and out. Mosses and hornworts have stomata, but liverworts don't. Nonvascular plants also have a thin waxy covering, called a cuticle, to help prevent drying out. They don't have true leaves, stems, or roots, but they do have a dominant part of the plant called the gametophyte that can photosynthesize. Nonvascular plants absorb water through their root-like structures called rhizoids, and they rely on osmosis to transport water from cell to cell. Rhizoids also provide support for the plant, and the cellulose in the cell walls helps keep the plant structured outside of a watery environment (see Fig. 2).
All land plants share a life cycle mechanism called the alternation of generations. This means that they go through both a multicellular diploid stage (sporophyte) and a multicellular haploid stage (gametophyte). Nonvascular plants also follow this basic structure in their life cycle. Here's more detail on each step (see Fig. 3):
The life cycle of nonvascular plants follows the alternation of generations, meaning they have both a multicellular diploid stage (sporophyte) and a multicellular haploid stage (gametophyte). The sporophyte produces spores via meiosis in a structure called a sporangium. These spores are unicellular and haploid. They will grow into a multicellular haploid plant called a gametophyte that has chloroplasts for photosynthesis. The gametophyte has sex organs called gametangia, which have archegonium for female sex organs and antheridium for male sex organs. The eggs and sperm are produced through mitosis. In nonvascular plants, water is needed for fertilization, as the sperm needs to swim to the egg. Once the sperm reaches the egg, the diploid sporophyte grows out of the archegonium and relies on the gametophyte for nutrients. The sporophyte is not independent. The life cycle restarts when the sporophytes produce spores via meiosis, which are released to grow into new gametophytes (see Fig. 3).
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.
Let's take a look at some of the similarities and differences between nonvascular and vascular plants.
Nonvascular and vascular plants share many similarities despite their differences. Both have mechanisms for protecting their embryos from drying out using maternal tissue. They also follow the alternation of generations life cycle, which involves a diploid and haploid stage. Both nonvascular and vascular plants have stomata, except for liverworts, to allow for gas exchange. Additionally, both groups of plants have mutualistic relationships with fungi, which help them access nutrients more easily. Cuticles are also present in both types of plants, with vascular plants having more developed cuticles that provide better protection against drying out. These similarities show that nonvascular and vascular plants have evolved similar strategies to survive and thrive in their environments.
See the table below comparing nonvascular and vascular plant differences (Table 1).
Nonvascular plants, such as mosses, liverworts, and hornworts, may not have the flashy features of other plants, but they are important in our environment. They help hold riverbanks together and prevent erosion, and they are often the first plants to colonize an area after a disaster or extinction event, making the soil more hospitable for other plant and animal life. Nonvascular plants have adapted to living on land with thin cuticles, stomata (except liverworts), relationships with fungi, and root-like structures called rhizoids. The haploid gametophyte is the dominant generation of nonvascular plants, and the diploid sporophyte is dependent on it. Nonvascular plants reproduce both sexually and asexually, with haploid spores growing into gametophytes and eggs and sperm being made through mitosis. Understanding the importance and unique characteristics of nonvascular plants is essential to appreciating the diversity and complexity of life on our planet.
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: Nonvascular plants DO NOT have vascular systems, vascular plants do contain vascular systems.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.Nonvascular plants have a dominant haploid gametophyte generation. Vascular plants have a dominant diploid sporophyte generation.Nonvascular plants remain small in size and cannot grow tall because they have no vascular system. Vascular plants can grow large and tall.Nonvascular plants are the mosses, hornworts, and liverworts. Vascular plants make up 80% of all plant species, including flowering plants.
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