What makes a seedless plant seedless

Bryophytes may have been successful at the transition from an aquatic habitat to land, but they are still dependent on water for reproduction, and absorb moisture and nutrients through the gametophyte surface. The lack of roots for absorbing water and minerals from the soil, as well as a lack of reinforced conducting cells, limits bryophytes to small sizes.

Although they may survive in reasonably dry conditions, they cannot reproduce and expand their habitat range in the absence of water. Vascular plants, on the other hand, can achieve enormous heights, thus competing successfully for light.

Photosynthetic organs become leaves, and pipe-like cells or vascular tissues transport water, minerals, and fixed carbon throughout the organism. In seedless vascular plants, the diploid sporophyte is the dominant phase of the lifecycle.

The gametophyte is now an inconspicuous, but still independent, organism. Throughout plant evolution, there is an evident reversal of roles in the dominant phase of the lifecycle. Seedless vascular plants still depend on water during fertilization, as the sperm must swim on a layer of moisture to reach the egg. This step in reproduction explains why ferns and their relatives are more abundant in damp environments.

The first fossils that show the presence of vascular tissue date to the Silurian period, about million years ago. The simplest arrangement of conductive cells shows a pattern of xylem at the center surrounded by phloem. Xylem is the tissue responsible for the storage and long-distance transport of water and nutrients, as well as the transfer of water-soluble growth factors from the organs of synthesis to the target organs.

The tissue consists of conducting cells, known as tracheids, and supportive filler tissue, called parenchyma. Xylem conductive cells incorporate the compound lignin into their walls, and are thus described as lignified. Lignin itself is a complex polymer that is impermeable to water and confers mechanical strength to vascular tissue. With their rigid cell walls, the xylem cells provide support to the plant and allow it to achieve impressive heights.

Tall plants have a selective advantage by being able to reach unfiltered sunlight and disperse their spores or seeds further away, thus expanding their range.

By growing higher than other plants, tall trees cast their shadow on shorter plants and limit competition for water and precious nutrients in the soil.

Phloem is the second type of vascular tissue; it transports sugars, proteins, and other solutes throughout the plant. Phloem cells are divided into sieve elements conducting cells and cells that support the sieve elements. Together, xylem and phloem tissues form the vascular system of plants.

Roots are not well preserved in the fossil record. Nevertheless, it seems that roots appeared later in evolution than vascular tissue. The development of an extensive network of roots represented a significant new feature of vascular plants. Thin rhizoids attached bryophytes to the substrate, but these rather flimsy filaments did not provide a strong anchor for the plant; neither did they absorb substantial amounts of water and nutrients. In contrast, roots, with their prominent vascular tissue system, transfer water and minerals from the soil to the rest of the plant.

The extensive network of roots that penetrates deep into the soil to reach sources of water also stabilizes trees by acting as a ballast or anchor. The majority of roots establish a symbiotic relationship with fungi, forming mycorrhizae, which benefit the plant by greatly increasing the surface area for absorption of water and soil minerals and nutrients.

A third innovation marks the seedless vascular plants. Accompanying the prominence of the sporophyte and the development of vascular tissue, the appearance of true leaves improved their photosynthetic efficiency.

Leaves capture more sunlight with their increased surface area by employing more chloroplasts to trap light energy and convert it to chemical energy, which is then used to fix atmospheric carbon dioxide into carbohydrates. The carbohydrates are exported to the rest of the plant by the conductive cells of phloem tissue. The existence of two types of morphology suggests that leaves evolved independently in several groups of plants.

A microphyll is small and has a simple vascular system. A single unbranched vein —a bundle of vascular tissue made of xylem and phloem—runs through the center of the leaf. Microphylls may have originated from the flattening of lateral branches, or from sporangia that lost their reproductive capabilities.

Megaphylls most likely appeared independently several times during the course of evolution. Their complex networks of veins suggest that several branches may have combined into a flattened organ, with the gaps between the branches being filled with photosynthetic tissue. In addition to photosynthesis, leaves play another role in the life of the plants. Pine cones, mature fronds of ferns, and flowers are all sporophylls —leaves that were modified structurally to bear sporangia.

Strobili are cone-like structures that contain sporangia. They are prominent in conifers and are commonly known as pine cones.

By the late Devonian period, plants had evolved vascular tissue, well-defined leaves, and root systems. With these advantages, plants increased in height and size. During the Carboniferous period, swamp forests of club mosses and horsetails—some specimens reaching heights of more than 30 m ft —covered most of the land. These forests gave rise to the extensive coal deposits that gave the Carboniferous its name.

In seedless vascular plants, the sporophyte became the dominant phase of the lifecycle. Water is still required for fertilization of seedless vascular plants, and most favor a moist environment. Modern-day seedless tracheophytes include club mosses, horsetails, ferns, and whisk ferns.

In the club mosses such as Lycopodium clavatum , sporangia are arranged in clusters called strobili. The club mosses , or phylum Lycopodiophyta , are the earliest group of seedless vascular plants. They dominated the landscape of the Carboniferous, growing into tall trees and forming large swamp forests.

The phylum Lycopodiophyta consists of close to 1, species, including the quillworts Isoetales , the club mosses Lycopodiales , and spike mosses Selaginellales , none of which are true mosses or bryophytes. Lycophytes follow the pattern of alternation of generations seen in the bryophytes, except that the sporophyte is the major stage of the lifecycle.

The gametophytes do not depend on the sporophyte for nutrients. Some gametophytes develop underground and form mycorrhizal associations with fungi. In club mosses, the sporophyte gives rise to sporophylls arranged in strobili, cone-like structures that give the class its name. Lycophytes can be homosporous or heterosporous.

Horsetails, whisk ferns and ferns belong to the phylum Monilophyta, with horsetails placed in the Class Equisetopsida. The single genus Equisetum is the survivor of a large group of plants, known as Arthrophyta, which produced large trees and entire swamp forests in the Carboniferous. The plants are usually found in damp environments and marshes Figure Leaves and branches come out as whorls from the evenly spaced joints. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem Figure Thin leaves originating at the joints are noticeable on the horsetail plant.

Horsetails were once used as scrubbing brushes and were nicknamed scouring brushes. Silica collects in the epidermal cells, contributing to the stiffness of horsetail plants.

Underground stems known as rhizomes anchor the plants to the ground. Modern-day horsetails are homosporous and produce bisexual gametophytes. The whisk fern Psilotum nudum has conspicuous green stems with knob-shaped sporangia. 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, and small yellow knobs form at the tip of the branch stem and contain the sporangia. Whisk ferns were considered an 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.

With their large fronds, ferns are the most readily recognizable seedless vascular plants. They are considered 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 tropics to temperate forests.

Some specimens of this short tree-fern species can grow very tall. Although some species survive in dry environments, most ferns are restricted to moist, shaded places. Ferns made their appearance in the fossil record during the Devonian period and expanded during the Carboniferous. The dominant stage of the lifecycle of a fern is the sporophyte, which consists of large compound leaves called fronds.

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. Croziers, or fiddleheads, are the tips of fern fronds. This life cycle of a fern shows alternation of generations with a dominant sporophyte stage.

Sori appear as small bumps on the underside of a fern frond. Most ferns produce the same type of spores and are therefore homosporous. The diploid sporophyte is the most conspicuous stage of the lifecycle.

On the underside of its mature fronds, sori singular, sorus form as small clusters where sporangia develop Figure Inside the sori, spores are produced by meiosis and released into the air. Those that land on a suitable substrate germinate and form a heart-shaped gametophyte, which is attached to the ground by thin filamentous rhizoids Figure The inconspicuous gametophyte harbors both sex gametangia.

Flagellated sperm released from the antheridium swim on a wet surface to the archegonium, where the egg is fertilized. The newly formed zygote grows into a sporophyte that emerges from the gametophyte and grows by mitosis into the next generation sporophyte.

Shown here are a young sporophyte upper part of image and a heart-shaped gametophyte bottom part of image. 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. This landscaped border at a college campus was designed by students in the horticulture and landscaping department of the college.

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. 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 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 rapidly once water is again available.

Mosses are at the base of the food chain in the tundra biome. Many species—from small 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. At the end of the nineteenth century, scientists observed that lichens and mosses were becoming increasingly rare in urban and suburban areas.

Since bryophytes have neither a root system for absorption of water and nutrients, nor a cuticle layer that protects them from desiccation, pollutants in rainwater readily penetrate their tissues; 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 bioindicator 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 by spreading rhizomes in the soil.

The water ferns of the genus Azolla harbor nitrogen-fixing cyanobacteria and restore this important nutrient to aquatic habitats. Sphagnum acutifolium is dried peat moss and can be used as fuel. By the Late Devonian period million years ago , plants had evolved vascular tissue, well-defined leaves, and root systems. With these advantages, plants increased in height and size. During the Carboniferous period — million years ago , swamp forests of club mosses and horsetails, with some specimens reaching more than 30 meters tall, covered most of the land.

These forests gave rise to the extensive coal deposits that gave the Carboniferous its name. In seedless vascular plants, the sporophyte became the dominant phase of the lifecycle. Water is still required for fertilization of seedless vascular plants, and most favor a moist environment. Modern-day seedless vascular plants include club mosses, horsetails, ferns, and whisk ferns.

The club mosses , or Lycophyta, are the earliest group of seedless vascular plants. They dominated the landscape of the Carboniferous period, growing into tall trees and forming large swamp forests. The division Lycophyta consists of close to 1, species, including quillworts Isoetales , club mosses Lycopodiales , and spike mosses Selaginellales : none of which is a true moss. Ferns and whisk ferns belong to the division Pterophyta. A third group of plants in the Pterophyta, the horsetails, is sometimes classified separately from ferns.

Horsetails have a single genus, Equisetum. They are the survivors of a large group of plants, known as Arthrophyta, which produced large trees and entire swamp forests in the Carboniferous.

The plants are usually found in damp environments and marshes [Figure 6]. Leaves and branches come out as whorls from the evenly spaced rings. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem [Figure 7].

Ferns are considered the most advanced seedless vascular plants and display characteristics commonly observed in seed plants. 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. Login processing Chapter Plant Structure, Growth, and Nutrition. Chapter 1: Scientific Inquiry. Chapter 2: Chemistry of Life. Chapter 3: Macromolecules.

Chapter 4: Cell Structure and Function. Chapter 5: Membranes and Cellular Transport. Chapter 6: Cell Signaling. Chapter 7: Metabolism. Chapter 8: Cellular Respiration. Chapter 9: Photosynthesis. Chapter Cell Cycle and Division. Chapter Meiosis. Chapter Classical and Modern Genetics. Chapter Gene Expression. Chapter Biotechnology. Chapter Viruses. Chapter Nutrition and Digestion. Chapter Nervous System. Chapter Sensory Systems. Chapter Musculoskeletal System. Chapter Endocrine System.

Chapter Circulatory and Pulmonary Systems. Chapter Osmoregulation and Excretion. Chapter Immune System. Chapter Reproduction and Development. Cell division occurs in the apical meristem. Root growth begins with seed germination. When the plant embryo emerges from the seed, the radicle of the embryo forms the root system.

The tip of the root is protected by the root cap, a structure exclusive to roots and unlike any other plant structure. The root cap is continuously replaced because it gets damaged easily as the root pushes through soil. The root tip can be divided into three zones: a zone of cell division, a zone of elongation, and a zone of maturation and differentiation. The zone of cell division is closest to the root tip; it is made up of the actively-dividing cells of the root meristem.

The zone of elongation is where the newly-formed cells increase in length, thereby lengthening the root. Beginning at the first root hair is the zone of cell maturation where the root cells begin to differentiate into special cell types.

All three zones are in the first centimeter or so of the root tip. Modified roots : Many vegetables are modified roots, such as radishes and carrots, which store energy in the form of starches and sugars.

The vascular tissue in the root is arranged in the inner portion of the root, which is called the vascular cylinder. A layer of cells, known as the endodermis, separates the vascular tissue from the ground tissue in the outer portion of the root. A waxy substance called suberin is present on the walls of the endodermal cells. This waxy region, known as the Casparian strip, forces water and solutes to cross the plasma membranes of endodermal cells instead of slipping between the cells.

This ensures that only materials required by the root pass through the endodermis, while toxic substances and pathogens are generally excluded. In dicot roots, the xylem and phloem of the stele are arranged alternately in an X shape, whereas in monocot roots, the vascular tissue is arranged in a ring around the pith.

Root structures may be modified for specific purposes. For example, some roots are bulbous and store starch. Aerial roots and prop roots are two forms of aboveground roots that provide additional support to anchor the plant.

Tap roots, such as carrots, turnips, and beets, are examples of roots that are modified for food storage. Ferns, club mosses, horsetails, and whisk ferns are seedless vascular plants that reproduce with spores and are found in moist environments.

Water is required for fertilization of seedless vascular plants; most favor a moist environment. Modern-day seedless tracheophytes include lycophytes and monilophytes. The club mosses, or phylum Lycopodiophyta, are the earliest group of seedless vascular plants. They dominated the landscape of the Carboniferous, growing into tall trees and forming large swamp forests.

The phylum Lycopodiophyta consists of close to 1, species, including the quillworts Isoetales , the club mosses Lycopodiales , and spike mosses Selaginellales , none of which are true mosses or bryophytes. Lycophytes follow the pattern of alternation of generations seen in the bryophytes, except that the sporophyte is the major stage of the life cycle. The gametophytes do not depend on the sporophyte for nutrients.

Some gametophytes develop underground and form mycorrhizal associations with fungi. In club mosses, the sporophyte gives rise to sporophylls arranged in strobili, cone-like structures that give the class its name.

Lycophytes can be homosporous or heterosporous. Strobili of club mosses : In some club mosses such as Lycopodium clavatum , sporangia are arranged in clusters called strobili.

Horsetails, whisk ferns, and ferns belong to the phylum Monilophyta, with horsetails placed in the Class Equisetopsida. The single extant genus Equisetum is the survivor of a large group of plants, which produced large trees, shrubs, and vines in the swamp forests in the Carboniferous.

The plants are usually found in damp environments and marshes. Leaves and branches come out as whorls from the evenly-spaced joints. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem. Leaves of a horsetail : The whorls of green structures at the joints are actually stems. The leaves are barely noticeable as brown rings just above each joint. Horsetails were once used as scrubbing brushes and so were called scouring rushes.

Silica collects in the epidermal cells, contributing to the stiffness of horsetail plants. Underground stems known as rhizomes anchor the plants to the ground. Modern-day horsetails are homosporous and produce bisexual gametophytes. While most ferns form large leaves and branching roots, the whisk ferns, Class Psilotopsida, lack both roots and leaves, which were probably lost by reduction.

Photosynthesis takes place in their green stems; small yellow knobs form at the tip of the branch stem and contain the sporangia. Whisk ferns were considered an early pterophytes. However, recent comparative DNA analysis suggests that this group may have lost both leaves and roots through evolution and is more closely related to ferns.

With their large fronds, ferns are the most-readily recognizable seedless vascular plants.