Biological Sciences
Nonvascular Plants
Nonvascular plants, also known as bryophytes, are a group of plants that lack specialized tissues for transporting water and nutrients. They are typically small and found in moist environments. Nonvascular plants include mosses, liverworts, and hornworts. These plants rely on diffusion and osmosis to absorb water and nutrients, and they play important roles in ecosystems as pioneers in colonizing bare substrates.
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5 Key excerpts on "Nonvascular Plants"
- Cecie Starr, Christine Evers, Lisa Starr, , Cecie Starr, Cecie Starr, Christine Evers, Lisa Starr(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
15.3 Nonvascular Plants LEARNING OBJECTIVES ●●● ● Explain why Nonvascular Plants tend to be low growing. ●●● ● Describe the life cycle of a moss. ●●● ● Give an example of an economically important moss. All Nonvascular Plants (plants that lack xylem and phloem) were traditionally grouped together as bryophytes. The term “bryophyte” is still used as an informal designation for a nonvascular plant. However, biologists now recognize three dis- tinct nonvascular lineages: the mosses, liverworts, and hornworts. Nonvascular Plants are the only plants in which the gametophyte is larger and longer-lived than the sporophyte. However, even the gametophytes of these plants tend to be low growing. One constraint on their size is their lack of vascular tissue. Without internal pipelines, materials cannot move efficiently through a tall plant body. Reproductive factors also keep Nonvascular Plants small. All Nonvascular Plants produce flagellated sperm that must swim to eggs. The low, mat-like growth form of their gametophytes minimizes the distance that sperm must swim to reach an egg. Moss Life Cycle Mosses are the largest group of the Nonvascular Plants and the most familiar, so they will be our main focus here. As an example of a nonvascular plant life cycle, consider the life of the haircap moss (Figure 15.5). Haploid gametophytes of this moss are present year-round as small, free-living plants. The gametophyte has leaf- like photosynthetic parts arrayed around a central stalk. Threadlike structures called rhizoids extend from the base of the gametophyte and hold it in place. Moss sporophytes appear only periodically. They lack chloroplasts and spend their life attached to and dependent on a gametophyte. The sporophyte body is dip- loid and consists of an unbranched stalk with a spore-producing organ (a sporan- gium) at its tip. Meiosis of cells inside a spore chamber yields haploid spores 1 . The sporophyte releases its spores, then degenerates.
eBook - ePub- Patricia Barnes-Svarney, Thomas E. Svarney(Authors)
- 2014(Publication Date)
- Visible Ink Press(Publisher)
Bryophytes —These are the Nonvascular Plants. Because bryophytes lack a system for conducting water and nutrients, they are restricted in size and live in moist areas close to the ground. Examples of bryophytes are mosses, liverworts, and hornworts and are most often found in moist environments—mainly because they require water to reproduce sexually. (However, species inhabit almost every environment, from hot, dry deserts to the coldest regions of the Antarctica continent.) Overall, they are the second largest group of land plants after flowering plants. They are generally small, compact plants that rarely grow to more than 8 inches (20 centimeters) tall. They have parts that appear leaflike, stemlike, and rootlike and lack vascular tissue (xylem and phloem). Most species have certain structures that help them to retain moisture around their sperm-producing and egg-producing structures and large gametophytes that hold on to sporophytes.Tracheophytes —These are the vascular plants, which are further divided into seedless plants and those that contain seeds. Plants with seeds are divided into flowering and nonflowering groups. Examples of seedless, vascular plants are ferns, horsetails, and club mosses. The cone-bearing conifers are seed-bearing, nonflowering vascular plants. It’s interesting to note that the majority of plants on Earth are seed-bearing, flowering, vascular plants—known as angiosperms.BRYOPHYTES
Why are bryophytes important to the study of early plants?
Some scientists believe bryophytes called liverworts are some of the closest living relatives of early land plants; they are thought to have evolved from freshwater, multicellular, green algae. Fossils of liverwort plants were found in 2010 in the Central Andean Basin of northwest Argentina. The scientists who made the discovery believe that this bryophyte plant—which lacked stems or roots—may be evidence that plants evolved on land ten million years earlier than previously thought. They found spores from the liverwort fossil that dated from between 473 and 471 million years ago, making these very simple plants the oldest land plant remains found to date.
eBook - PDFBiology Today
An Issues Approach
- Eli Minkoff, Pamela Baker(Authors)
- 2003(Publication Date)
- Garland Science(Publisher)
The simplest plants containing separate types of tissues are the mosses, liverworts, and hornworts, often grouped as Bryophyta and also known as Nonvascular Plants. The most familiar and ecologically dominant group of plants are the vascular plants , including all plants that have vascular (conducting) tis-sues that transport fluids, generally through tubular cells surrounded by rigid cell walls. Vascular plants contain two types of conducting tissue: 378 THOUGHT QUESTIONS 1 Why do you think plants take up NO 3 – or NO 2 – ions but not NH 4 + ions? 2 Some plants have mutualistic associations with bacteria in root nodules. Do humans also have mutualistic associations with bacteria? 3 What is the definition of acidity? How does the uptake of NH 4 + ions by some plants make the soil around them more acidic? CONNECTIONS CHAPTER 6 Plants Use Specialized Tissues and Transport Mechanisms 379 xylem, which usually conducts water and minerals upward, and phloem, which conducts a water solution of photosynthetic products (mostly sugars) in both directions but more often downward. The existence of these vascular tissues allows the parts of the plant to specialize (Figure 11.9). The roots grow underground, anchor the plant in the soil, and absorb water and dissolved nutrients. The vascular tissues conduct the water and nutrients from the roots through the xylem of the stem to the above-ground parts, where the water is needed for both photosynthesis and support of the upper parts of the plant. The roots can receive photo-synthetic products through the phloem from the chlorophyll-containing tissues above. Roots thus need not contain chlorophyll or carry out pho-tosynthesis themselves, so they are not green and do not require light. Vascular tissues have rigid cell walls, and, as we see in the next sec-tion, water pressure makes plant tissues even stronger as well as helping plants to stand upright.
eBook - PDFGreen Plants
Their Origin and Diversity
- Peter R. Bell, Alan R. Hemsley(Authors)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
General features of the bryophytes The mosses and liverworts, although morphologi-cally somewhat dissimilar, are classified together as the Bryophyta. Because of their distinctive fea-tures they are treated as a division of the plant kingdom, of a rank equal to that of the algal groups and the Tracheophyta (Table 1.2). There are about 25 000 species of bryophytes in all. Three classes are recognized, namely Marchantiopsida, Anthocerotopsida and Bryopsida. They represent the simplest of the archegoniate plants and form a single division with the following characteris-tics: BRYOPHYTA Habitat Mainly terrestrial. Plastid pigments Chlorophylls a , b ; -carotene; xanthophyll (lutein). Food reserves Starch, to a lesser extent fats and oils. Cell wall components Cellulose, hemicelluloses. Reproduction Heteromorphic life cycle, the gametophytic phase normally the more con-spicuous, and the sporophytic determinate and partly dependent upon it. Sex organs with a jacket of sterile cells, the egg cells enclosed singly in flask-shaped archegonia. Zooidogamous, spermatozoids with two whiplash flagella. Embryogeny exoscopic. Sporophyte producing non-motile, cutinized spores, in some species with heavily thick-ened and sculptured walls, usually all of one size (homospory). Vegetative propagation of the gametophyte by fragmentation or spe-cialized gemmae. Growth forms of gametophyte Thallus flattened, with some internal gametophyte differentia-tion, or consisting of a main axis with leafy appendages. Although the simplest terrestrial plants, the bryo-phytes in some parts of the world form a conspic-uous component of the vegetation. They are, for example, prominent amongst the epiphytes of mist forests of tropical mountains. Some species form dense communities submerged in antarctic lakes. Vast bogs in the northern hemisphere have been built up largely by the growth of the moss Sphagnum .
eBook - ePub- (Author)
- 2008(Publication Date)
- Trade Paper Press(Publisher)
lignin naturally occurring substance produced by plants to strengthen their tissues. It is difficult for enzymes to attack lignin, so living organisms cannot digest wood, with the exception of a few specialized fungi and bacteria. Lignin is the essential ingredient of all wood and is, therefore, of great commercial importance.liverwort nonvascular plant (with no “veins” to carry water and food), related to hornworts and mosses; it is found growing in damp places. (Division Bryophyta.)meristem region of plant tissue containing cells that are actively dividing to produce new tissues (or have the potential to do so).mesophyll the tissue between the upper and lower epidermis of a leaf blade (lamina), consisting of parenchyma-like cells containing numerous chloroplasts.micropyle in flowering plants, a small hole toward one end of the ovule. At pollination the pollen tube growing down from the stigma eventually passes through this pore.monocotyledon angiosperm (flowering plant) having an embryo with a single cotyledon, or seed leaf (as opposed to dicotyledons, which have two).monoecious having separate male and female flowers on the same plant. Monoecism is a way of avoiding self-fertilization.moss small nonflowering plant of the class Musci, forming with the liverworts and the hornworts the division Bryophyta.mycorrhiza mutually beneficial (mutualistic) association occurring between plant roots and a soil fungus. Mycorrhizal roots take up nutrients more efficiently than nonmycorrhizal roots, and the fungus benefits by obtaining carbohydrates from the plant or tree.nastic movement plant movement that is caused by an external stimulus, such as light or temperature, but is directionally independent of its source, unlike tropisms. Nastic movements occur as a result of changes in water pressure within specialized cells or differing rates of growth in parts of the plant.nectar sugary liquid secreted by some plants from a nectary, a specialized gland usually situated near the base of the flower. Nectar attracts insects, birds, bats, and other animals to the flower for
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