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An unexpected error occurred. Previous Video The seedless vascular plants were the first to evolve specialized vascular systems—an adaptation that helped them become the first tall plants on Earth. Today, seedless vascular plants are represented by lycophytes and monilophytes. Lycophytes include clubmosses, spikemosses, and quillworts. Notably, none of the lycophytes are true mosses, which are nonvascular plants.
Monilophytes include ferns, horsetails, and whisk ferns and their relatives. Like all plants, seedless vascular plants display an alternation of generations in their life cycle, as shown here using a fern plant as an example. This means that they spend part of their life cycle as a haploid gametophyte, and the other part as a diploid sporophyte. Like nonvascular plants, seedless vascular plants reproduce using spores, rather than seeds. The spores are haploid, and are dispersed by structures called sori, clustered on the underside of the leaves.
The sori themselves contain many sporangia. Upon reaching maturity, these sporangia open, dispersing the haploid spores. The spores then grow via mitosis to form the haploid gametophyte.
At the gametophyte stage - which is typically very small and found on or just below the soil surface - haploid gametes are formed by mitosis. A single gametophyte is bisexual and develops two different structures - the antheridia and archegonia - that produce gametes in male and female forms respectively.
Like the nonvascular plants, the male sperm gamete is flagellated and requires water to travel to the female gamete, following a chemical attractant to find the egg. Because the gametes in a single gametophyte will be genetically identical due to their haploid origin, crosses typically occur between different gametophytes. Ferns can prevent any self-fertilization by having their antheridia and archegonia mature at different times.
Finally, the fertilized egg will grow a new diploid sporophyte from the diploid zygote of the gametophyte, completing the life cycle. Like seed plants, seedless vascular plants have life cycles dominated by sporophytes. However, unlike either of the other major plant lineages, their smaller gametophytes can live independently—meaning they do not provide nourishment to the sporophyte, or require it from the sporophyte.
Arguably the key feature of seedless vascular plants is their specialized network of vascular tissue, akin to that of the seed plants. This adaptation allowed them to transport water, nutrients, and other organic materials, and to attain greater sizes—which distinguished them from their nonvascular relatives.
Today, seedless vascular plants are represented by monilophytes and lycophytes. Ferns—the most common seedless vascular plants—are monilophytes. Whisk ferns and their relatives and horsetails are also monilophytes. Lycophytes include club mosses, spikemosses, and quillworts—none of which are true mosses. Unlike nonvascular plants, vascular plants—including seedless vascular plants—have an extensive network of vascular tissue comprised of xylem and phloem. Most seedless vascular plants also have true roots and leaves.
Furthermore, the life cycles of seedless vascular plants are dominated by diploid spore-producing sporophytes, rather than gametophytes. However, like nonvascular plants, seedless vascular plants reproduce with spores rather than seeds.
Seedless vascular plants are also typically more reproductively successful in moist environments because their sperm require a film of water to reach the eggs.
Like animals, seedless vascular plants and other plants alternate between meiosis and fertilization during reproduction. Meiosis is a cell division process that produces haploid cells—which contain one complete set of chromosomes—from a diploid cell—which contains two complete sets of chromosomes. While most ferns form large leaves and branching roots, the whisk ferns , class Psilotopsida, lack both roots and leaves, probably lost by reduction.
Photosynthesis takes place in their green stems, which branch dichotomously. Small yellow knobs form at the tip of a branch or at branch nodes and contain the sporangia Figure. Spores develop into gametophytes that are only a few millimeters across, but which produce both male and female gametangia.
Whisk ferns were considered early pterophytes. However, recent comparative DNA analysis suggests that this group may have lost both vascular tissue and roots through evolution, and is more closely related to ferns. Phylum Monilophyta: Class Polypodiopsida True Ferns With their large fronds, the true ferns are perhaps the most readily recognizable seedless vascular plants.
They are also considered to be the most advanced seedless vascular plants and display characteristics commonly observed in seed plants. More than 20, species of ferns live in environments ranging from the tropics to temperate forests. Although some species survive in dry environments, most ferns are restricted to moist, shaded places. The dominant stage of the life cycle of a fern is the sporophyte, which consists of large compound leaves called fronds.
Fronds may be either finely divided or broadly lobed. Fronds fulfill a double role; they are photosynthetic organs that also carry reproductive organs. The stem may be buried underground as a rhizome, from which adventitious roots grow to absorb water and nutrients from the soil; or, they may grow above ground as a trunk in tree ferns Figure.
Adventitious organs are those that grow in unusual places, such as roots growing from the side of a stem. The tip of a developing fern frond is rolled into a crozier, or fiddlehead Figure.
Fiddleheads unroll as the frond develops. On the underside of each mature fern frond are groups of sporangia called sori Figure a. Most ferns are homosporous. Spores are produced by meiosis and are released into the air from the sporangium. Those that land on a suitable substrate germinate and form a heart-shaped gametophyte, or prothallus, which is attached to the ground by thin filamentous rhizoids Figure b.
Gametophytes produce both antheridia and archegonia. Like the sperm cells of other pterophytes, fern sperm have multiple flagella and must swim to the archegonium, which releases a chemoattractant to guide them. The zygote develops into a fern sporophyte, which emerges from the archegonium of the gametophyte. Maturation of antheridia and archegonia at different times encourages cross-fertilization. The full life cycle of a fern is depicted in Figure. Visual Connection Reproductive cycle of a fern.
This life cycle of a fern shows alternation of generations with a dominant sporophyte stage. They were also familiar with the biology of the plants they chose. Among his many interests, Jefferson maintained a strong passion for botany.
A landscape designer will plan traditional public spaces—such as botanical gardens, parks, college campuses, gardens, and larger developments—as well as natural areas and private gardens. The restoration of natural places encroached on by human intervention, such as wetlands, also requires the expertise of a landscape designer. Coursework in architecture and design software is also required for the completion of the degree. The successful design of a landscape rests on an extensive knowledge of plant growth requirements such as light and shade, moisture levels, compatibility of different species, and susceptibility to pathogens and pests.
Mosses and ferns will thrive in a shaded area, where fountains provide moisture; cacti, on the other hand, would not fare well in that environment. The future growth of individual plants must be taken into account, to avoid crowding and competition for light and nutrients.
The appearance of the space over time is also of concern. Shapes, colors, and biology must be balanced for a well-maintained and sustainable green space. Art, architecture, and biology blend in a beautifully designed and implemented landscape Figure. The Importance of Seedless Plants Mosses and liverworts are often the first macroscopic organisms to colonize an area, both in a primary succession—where bare land is settled for the first time by living organisms, or in a secondary succession—where soil remains intact after a catastrophic event wipes out many existing species.
Their spores are carried by the wind, birds, or insects. Once mosses and liverworts are established, they provide food and shelter for other plant species. In a hostile environment, like the tundra where the soil is frozen, bryophytes grow well because they do not have roots and can dry and rehydrate quickly once water is again available.
Mosses are at the base of the food chain in the tundra biome. Many species—from small herbivorous insects to musk oxen and reindeer—depend on mosses for food.
In turn, predators feed on the herbivores, which are the primary consumers. Some reports indicate that bryophytes make the soil more amenable to colonization by other plants. Because they establish symbiotic relationships with nitrogen-fixing cyanobacteria, mosses replenish the soil with nitrogen. By the end of the nineteenth century, scientists had observed that lichens and mosses were becoming increasingly rare in urban and suburban areas. Because bryophytes have neither a root system for absorption of water and nutrients, nor a cuticular layer that protects them from desiccation, pollutants in rainwater readily penetrate their tissues as they absorb moisture and nutrients through their entire exposed surfaces.
Therefore, pollutants dissolved in rainwater penetrate plant tissues readily and have a larger impact on mosses than on other plants. The disappearance of mosses can be considered a biological indicator for the level of pollution in the environment.
Ferns contribute to the environment by promoting the weathering of rock, accelerating the formation of topsoil, and slowing down erosion as rhizomes spread throughout the soil. The water ferns of the genus Azolla harbor nitrogen-fixing cyanobacteria and restore this important nutrient to aquatic habitats. Seedless plants have historically played a role in human life with uses as tools, fuel, and medicine. For example, dried peat moss , Sphagnum , is commonly used as fuel in some parts of Europe and is considered a renewable resource.
Sphagnum bogs Figure are cultivated with cranberry and blueberry bushes. In addition, the ability of Sphagnum to hold moisture makes the moss a common soil conditioner. Even florists use blocks of Sphagnum to maintain moisture for floral arrangements! The attractive fronds of ferns make them a favorite ornamental plant.
Because they thrive in low light, they are well suited as house plants. More importantly, fiddleheads of bracken fern Pteridium aquilinum are a traditional spring food of Native Americans, and are popular as a side dish in French cuisine. The licorice fern, Polypodium glycyrrhiza, is part of the diet of the Pacific Northwest coastal tribes, owing in part to the sweetness of its rhizomes. It has a faint licorice taste and serves as a sweetener.
The rhizome also figures in the pharmacopeia of Native Americans for its medicinal properties and is used as a remedy for sore throat. Go to this website to learn how to identify fern species based upon their fiddleheads.
By far the greatest impact of seedless vascular plants on human life, however, comes from their extinct progenitors. The tall club mosses, horsetails, and tree-like ferns that flourished in the swampy forests of the Carboniferous period gave rise to large deposits of coal throughout the world.
Coal provided an abundant source of energy during the Industrial Revolution, which had tremendous consequences on human societies, including rapid technological progress and growth of large cities, as well as the degradation of the environment. Coal is still a prime source of energy and also a major contributor to global warming. The seedless vascular plants show several features important to living on land: vascular tissue, roots, and leaves.
Vascular systems consist of xylem tissue, which transports water and minerals, and phloem tissue, which transports sugars and proteins. With the development of the vascular system, leaves appeared to act as large photosynthetic organs, and roots to access water from the ground. Small uncomplicated leaves are termed microphylls. Large leaves with vein patterns are termed megaphylls. Modified leaves that bear sporangia are called sporophylls. Ferns form large leaves and branching roots.
In contrast, whisk ferns , the psilophytes, lack both roots and leaves, which were probably lost by evolutionary reduction. Evolutionary reduction is a process by which natural selection reduces the size of a structure that is no longer favorable in a particular environment.
Photosynthesis takes place in the green stem of a whisk fern. Small yellow knobs form at the tip of the branch stem and contain the sporangia. Whisk ferns have been classified outside the true ferns; however, recent comparative analysis of DNA suggests that this group may have lost both vascular tissue and roots through evolution, and is actually closely related to ferns. With their large fronds, ferns are the most readily recognizable seedless vascular plants [Figure 8]. About 12, species of ferns live in environments ranging from tropics to temperate forests.
Although some species survive in dry environments, most ferns are restricted to moist and shaded places. They made their appearance in the fossil record during the Devonian period — million years ago and expanded during the Carboniferous period, — million years ago [Figure 9].
Go to this website to see an animation of the lifecycle of a fern and to test your knowledge. Landscape Designer Looking at the well-laid gardens of flowers and fountains seen in royal castles and historic houses of Europe, it is clear that the creators of those gardens knew more than art and design.
They were also familiar with the biology of the plants they chose. A landscape designer will plan traditional public spaces—such as botanical gardens, parks, college campuses, gardens, and larger developments—as well as natural areas and private gardens [Figure 10]. The restoration of natural places encroached upon by human intervention, such as wetlands, also requires the expertise of a landscape designer.
Coursework in architecture and design software is also required for the completion of the degree. The successful design of a landscape rests on an extensive knowledge of plant growth requirements, such as light and shade, moisture levels, compatibility of different species, and susceptibility to pathogens and pests. For example, mosses and ferns will thrive in a shaded area where fountains provide moisture; cacti, on the other hand, would not fare well in that environment.
The future growth of the individual plants must be taken into account to avoid crowding and competition for light and nutrients. The appearance of the space over time is also of concern. Shapes, colors, and biology must be balanced for a well-maintained and sustainable green space. Art, architecture, and biology blend in a beautifully designed and implemented landscape.
Seedless nonvascular plants are small. The dominant stage of the life cycle is the gametophyte. Without a vascular system and roots, they absorb water and nutrients through all of their exposed surfaces. There are three main groups: the liverworts, the hornworts, and the mosses. They are collectively known as bryophytes. Vascular systems consist of xylem tissue, which transports water and minerals, and phloem tissue, which transports sugars and proteins. With the vascular system, there appeared leaves—large photosynthetic organs—and roots to absorb water from the ground.
The seedless vascular plants include club mosses, which are the most primitive; whisk ferns, which lost leaves and roots by reductive evolution; horsetails, and ferns. The bryophytes are divided into three divisions: the liverworts or Marchantiophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.
How did the development of a vascular system contribute to the increase in size of plants? It became possible to transport water and nutrients through the plant and not be limited by rates of diffusion. Vascularization allowed the development of leaves, which increased efficiency of photosynthesis and provided more energy for plant growth.
Skip to content Chapter Diversity of Plants. Learning Objectives By the end of this section, you will be able to: Describe the distinguishing traits of the three types of bryophytes Identify the new traits that first appear in seedless vascular plants Describe the major classes of seedless vascular plants. Careers in Action. Why do mosses grow well in the Arctic tundra? They grow better at cold temperatures. They do not require moisture. They do not have true roots and can grow on hard surfaces.
There are no herbivores in the tundra.
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