Seedless plants | Biology for Seniors II (2023)

classify seedless plants

An incredible variety of seedless plants populate the Earth's landscape. Mosses can grow on a tree trunk, and horsetails can flaunt their jointed stems and slender leaves on the forest floor. Today, seedless plants represent only a small fraction of the plants in our environment; However, three hundred million years ago, seedless plants dominated the landscape, growing in the vast swampy forests of the Carboniferous. Its decomposition created large deposits of coal that we mine today.

Current evolutionary thought holds that all plants, both green and terrestrial algae, are monophyletic; that is, they are descendants of a single common ancestor. The evolutionary transition from water to land imposed severe limitations on plants. They had to develop strategies to prevent dehydration, airborne reproductive cells, structural support, and to capture and filter sunlight. While seed plants developed adaptations that allowed them to colonize even the driest habitats on Earth, not all plants were completely independent of water. Most seedless plants still require a moist environment.

beginning of plant life

Kingdom Plantae is a large and diverse group of organisms. More than 300,000 species of plants have been catalogued. Of these, more than 260,000 are seed plants. Mosses, ferns, conifers, and flowering plants are all members of the plant kingdom. Most biologists also consider green algae to be plants, while others exclude all algae from the plant kingdom. The reason for this disagreement stems from the fact that only green algae, thecarophyte, share common traits with land plants (such as the use of chlorophyllamibmore carotene in the same proportion as plants). These properties are absent from other types of algae.

yours isinteractive websiteto get a deeper insight into charophytes.

Plant adaptations to life on land

As organisms adapted to life on land, they had to deal with various challenges in the terrestrial environment. Water is called the "stuff of life." The interior of the cell is a watery soup: it is in this medium that most small molecules dissolve and diffuse, and where most of the chemical reactions of metabolism take place. Dehydration, or dryness, is a constant threat to an organism exposed to air. Even if parts of a plant are close to a water source, aerial structures are likely to dry out. Water also gives organisms buoyancy. On land, plants need to develop structural support in an environment that does not offer the same support as water. The organism is also subject to bombardment by mutagenic radiation because the air does not filter the ultraviolet rays of sunlight. Also, the male gametes have to catch up with the female gametes with new strategies, since swimming is no longer possible. Therefore, both gametes and zygotes must be protected from desiccation. Successful land plants have developed strategies to meet all of these challenges. Not all settings appeared at once. Some species have never strayed far from the aquatic environment, while others have conquered the driest environments on land.

To balance these survival challenges, life on land offers several benefits. First, sunlight is abundant. The water acts as a filter, changing the spectral quality of the light absorbed by the photosynthetic pigment chlorophyll. Second, carbon dioxide is more readily available in air than in water because it diffuses more easily into the air. Third, land plants evolved before land animals; Therefore, no predators threatened plant life until the mainland was colonized by animals. This situation changed when the animals came out of the water and fed on the abundant sources of nutrients from the established flora. Plants, in turn, have evolved strategies to thwart predators: from thorns and prickles to toxic chemicals.

Like the first land animals, the first land plants lived near an abundant source of water and developed strategies to survive drought. Such a strategy is called leniency. For example, many mosses can dry out to a brown, brittle mat, but once rain or flood water makes the water available, the mosses will absorb it and restore their green, healthy appearance. Another strategy is to colonize high humidity environments where droughts are rare. Considered a lineage of early plants, ferns thrive in cool, moist places, like the undergrowth of temperate forests. Later, plants moved away from humid or aquatic environments using desiccation resistance instead of tolerance. These plants, like cacti, minimize water loss enough to survive in extremely dry environments.

The most successful adaptation solution was the development of new structures that gave plants an advantage in colonizing new, arid environments. Four main adaptations are found in all land plants: alternation of generations, a sporangium in which spores are formed, a gametangium that produces haploid cells, and apical meristem tissue in roots and shoots. The development of a waxy cuticle and a lignin-laden cell wall also contributed to the success of land plants. These adaptations are conspicuous by their absence in the closely related green algae, another reason for the debate over their classification in the plant kingdom.

generational relief

The alternation of generations describes a life cycle in which an organism exhibits haploid and diploid multicellular stages (Figure 2).

plotrefers to a life cycle in which there is a dominant haploid stage, anddiplomaticrefers to a life cycle in which diploid is the dominant life stage. The man is diplomatic. Most plants exhibit alternation of generations, described asHaplodiplodontia:The haploid multicellular form, the so-called gametophyte, is followed in the developmental sequence by a diploid multicellular organism, the sporophyte. The gametophyte produces gametes (reproductive cells) through mitosis. This may be the most obvious phase of the plant's life cycle, as in mosses, or it may appear in a microscopic structure, such as a pollen granule, in higher plants (a common collective term for vascular plants). The sporophyte stage is hardly recognizable in lower plants (collective term for mosses, liverworts, and lichens). Majestic trees are the diplomatic phase in the life cycle of plants like redwoods and pines.

Embryo protection is an important requirement for terrestrial plants. The vulnerable embryo must be protected from dehydration and other environmental hazards. In both seedless and seed-bearing plants, the female gametophyte provides protection and nutrients to the embryo as it develops into the new generation of sporophytes. This distinctive feature of land plants gave the group its alternate name.embryophytes.

sporangia in seedless plants

The sporophyte of seedless plants is diploid and results from the syngamy (fusion) of two gametes. The sporophyte bears the sporangia (singular, sporangium): organs that first appeared in land plants. The term "sporangium" literally means "spore in a container" as it is a reproductive sac that contains spores.sporocytes, or parent cells, produce haploid spores by meiosis, with the secondnorteChromosome number reduced to 1norte(Note that many plant sporophytes are polyploid: for example, durum wheat is tetraploid, bread wheat is hexaploid, and some ferns are 1000 ploid.) Subsequently, the spores are released from the sporangia and dispersed into the environment. Two different types of spores are produced in land plants, leading to segregation of the sexes at different points in the life cycle.Seedless plants without vesselsThey produce only one type of spores and are namedhomosporized🇧🇷 In these plants the gametophyte phase dominates. After germinating from a spore, the resulting gametophyte produces male and female gametangia, usually in the same individual. Unlike,heterosporadoPlants produce two morphologically distinct types of spores. The male spores are calledmicrosporic, due to its smaller size, and develop in the male gametophyte; the comparatively largestdustybecome the female gametophyte. Heterospory is seen in someSamenlose Gefäßpflanzenand in all seed plants.

When the haploid spore germinates in a hospitable environment, it produces a multicellular gametophyte through mitosis. The gametophyte supports the zygote formed by the fusion of gametes and the resulting young sporophyte (vegetative form). The cycle then starts all over again.

The spores of seedless plants are surrounded by thick cell walls that contain a tough polymer known assporopollenin🇧🇷 This complex substance is characterized by long chains of organic molecules related to fatty acids and carotenoids: hence the yellow color of most pollen. Sporopolenin is exceptionally resistant to chemical and biological degradation. In seed plants that use pollen to transfer male sperm to female ovule, sporopollenin resistance explains the existence of well-preserved pollen fossils. Sporopollenin was once considered an innovation of land plants; However, green algaeColeochaetesforms spores that contain sporopolenin.

Gametangium in seedless plants

gametangia(singular, gametangium) are structures found in multicellular haploid gametophytes. In the gametangium, gametes develop from progenitor cells by mitosis. The male gametangium (Antheridium) releases sperm. Many seedless plants produce sperm cells equipped with flagella that allow them to swim in a moist environment.archegon: the female gametangium. The embryo develops as a sporophyte within the archegonia. Gametangia are found in seedless plants, but are rarely found in seed plants.

meristemo apical

Plant shoots and roots grow further through rapid cell division in a tissue called the apical meristem, which is a small patch of cells located at the top of the stem or root tip (Figure 4). The apical meristem consists of undifferentiated cells that continue to multiply throughout the life of the plant. Meristematic cells give rise to all the specialized tissues of the body. The elongation of shoots and roots gives the plant access to additional space and resources: light in the case of the shoots, and water and minerals in the case of the roots. A separate meristem called the lateral meristem produces cells that increase the diameter of tree trunks.

Additional adaptations of land plants.

As plants adapted to dry land and became independent of the constant presence of water in moist habitats, new organs and structures emerged. The first land plants grew no more than a few inches above the ground and competed for light on these low mats. By developing a bud and growing larger, the individual plants absorbed more light. Because air offers much less support than water, land plants built stiffer molecules in their stems (and later in the trunks of trees). For small plants like B. unicellular algae, a simple diffusion is enough to distribute water and nutrients throughout the organism. However, for plants to evolve into larger forms, the development of vascular tissue for the distribution of water and solutes was a prerequisite. The vasculature contains xylem and phloem tissues. The xylem carries water and minerals taken from the soil to the shoot, while the phloem carries the food obtained through photosynthesis throughout the plant. A root system developed to absorb water and minerals from the soil and to anchor the shoot higher and higher in the soil.

In land plants, a waxy, waterproof covering protects the cuticle, leaves, and stems from drying out. However, the cuticle also prevents the absorption of carbon dioxide, which is necessary for the synthesis of carbohydrates through photosynthesis. To overcome this, stomata, or pores, which open and close to regulate the movement of gases and water vapor, arose in plants as they moved from humid environments to drier habitats.

Water filters out ultraviolet B (UVB) light, which is harmful to all organisms, especially those that need to absorb light to survive. This filtering does not occur in land plants. This posed an additional challenge for the colonization of land, which was met by the development of biosynthetic pathways for the synthesis of protective flavonoids and other compounds: pigments that absorb ultraviolet wavelengths of light and protect the aerial parts of plants. of photodynamic damage.

Plants cannot avoid being eaten by animals. Instead, they synthesize a variety of toxic secondary metabolites: complex organic molecules such as alkaloids whose noxious odor and unpleasant taste deter animals. These toxic compounds can also cause serious illness and even death and deter predators. Humans have used many of these compounds as medicines, remedies, or spices for centuries. In contrast, when plants co-evolved with animals, the evolution of sweet and nutritive metabolites attracted animals to provide valuable assistance in the dispersal of pollen grains, fruits, or seeds. Plants have recruited animals to help them in this way for hundreds of millions of years.

Evolution of land plants

No discussion of the evolution of land plants can be undertaken without a brief study of the time line of geological ages. The early era known as the Paleozoic is divided into six periods. It begins with the Cambrian, followed by the Ordovician, Silurian, Devonian, Carboniferous, and Permian. The main event that shaped the Ordovician, more than 500 million years ago, was the colonization of the land by the ancestors of modern land plants. Fossilized cells, cuticles, and spores of the earliest land plants have been dated to the Ordovician to early Paleozoic. The oldest known vascular plants have been identified in Devonian deposits. One of the richest sources of information is the Rhynie chert, a sedimentary rock deposit in Rhynie, Scotland (Figure 5) in which embedded fossils of some of the oldest vascular plants have been identified.

Paleobotanists distinguish betweenextinctspecies, such as fossils, andexistingspecies that are still alive. The extinct vascular plants, classified as zosterophytes and trimerophytes, probably lacked leaves and true roots, and formed clumps of low vegetation similar in size to modern mosses, although some trimethophytes could reach a meter in height. the later genreCooksonia, which flourished during the Silurian, has been extensively studied using well-preserved examples. impressions ofCooksoniathey show slender branching stems ending in what appear to be sporangia. From the specimens recovered, it cannot be determined with certainty whetherCooksoniaThey had vascular tissue. Fossils indicate that at the end of the Devonian, ferns, horsetail, and seed plants populated the landscape and gave rise to trees and forests. This lush vegetation helped oxygenate the atmosphere, making it easier for air-breathing animals to colonize the mainland. Plants also established early symbiotic relationships with fungi, creating mycorrhizae: a relationship in which the fungal network of filaments increases the efficiency of the plant's root system and the plants provide the fungus with byproducts of photosynthesis.

The main divisions of land plants.

Green algae and land plants are grouped together in a subphylum called Streptophytina and are therefore called streptophytes. In another subdivision, land plants are divided into two large groups based on the absence or presence of vascular tissue, as detailed in Figure 6. Plants that lack vascular tissue made up of specialized cells for transporting water and nutrients are callednon vascular plants🇧🇷 Hepaticas, mosses and tomentosum are seedless, non-vascular plants that probably appeared early in the evolution of land plants. Vascular plants have evolved a network of cells that conduct water and solutes. The first vascular plants appeared in the late Ordovician and probably resembled lycophytes, which include mosses (not to be confused with mosses) and pterophytes (ferns, horsetails, and ferns). Lycophytes and pterophytes are called seedless vascular plants because they do not produce seeds. Seed plants or spermatophytes form the largest group of all extant plants and thus characterize the landscape. Seed plants include the nudibranchs, particularly the conifers (gymnosperms) which produce 'naked seeds', and the most successful of all plants, the flowering plants (angiosperms). Angiosperms house their seeds in chambers in the center of a flower; the chamber walls then transform into a fruit.

Green algae: precursors of land plants

streptofiten

Until recently, all photosynthetic eukaryotes were considered members of the kingdom Plantae. However, the brown, red, and gold algae were assigned to the kingdom Protista. Because in addition to its ability to capture light energy and fix CO₂, lack many structural and biochemical features that distinguish plants from protists. The position of green algae is ambiguous. Green algae contain the same carotenoids and chlorophyllamiblike land plants, while other algae have other accessory pigments and types of chlorophyll molecules in addition to chlorophylla🇧🇷 Both green algae and land plants also store carbohydrates in the form of starch. Green algae cells divide along cell plates called phragmoplasts, and their cell walls are layered similar to embryophyte cell walls. Consequently, the closely related land plants and green algae are now part of a new monophyletic group called the Streptophyta.

The remaining green algae, which belong to a group called the Chlorophyta, include more than 7,000 different species that live in freshwater, brackish water, seawater, or snow patches. Some green algae even survive in soil as long as it is covered by a thin film of moisture in which to live. Periodic dry periods provide a selective advantage for algae that can survive water stress. You should already be familiar with some particular green algae.spirogyreand desmidos. Their cells contain chloroplasts, which come in a dizzying variety of shapes, and their cell walls contain cellulose, just like land plants. Some green algae are unicellular, such asChlorellamichlamydomonas, which increases the ambiguity of the classification of green algae since the plants are multicellular. Other algae likeulva(commonly called sea lettuce) form colonies (Figure 7).

Reproduction of green algae.

Green algae reproduce both asexually, by fragmentation or dispersal of spores, and sexually, producing gametes that fuse during fertilization. In a unicellular organism likechlamydomonas, there is no mitosis after fertilization. in the multicellular organismulva, a sporophyte grows by mitosis after fertilization. Both of themchlamydomonasmiulvaproduce flagellated gametes.

charales

Green algae of the order Charales and Coleochetes (microscopic green algae that coat their spores with sporopolenin) are thought to be the closest living relatives of embryophytes. Charales dates back 420 million years. They live in a variety of freshwater habitats and range in size from a few millimeters to a meter in length. The representative species isChar(Figure 8), often called musk grass or skunk grass due to its unpleasant odor. Large cells form the thallus: the main stem of the algae. The branches emanating from the nodes are made up of smaller cells. The male and female reproductive structures are found in the nodules, and the spermatozoa have flagella. Unlike land plants, charales do not undergo alternation of generations in their life cycle. Charales exhibit a number of traits that are significant to their adaptation to life on Earth. They produce the compounds lignin and sporopolenin and form plasmodesmata, which connect the cytoplasm of neighboring cells. The egg and then the zygote form in a protected chamber in the mother plant.

New information from a recent and extensive analysis of green algae DNA sequences indicates that zygnematales are more closely related to embryophytes than to charales. Zygnematoles belong to the genus of the familyspirogyre.As DNA analysis techniques improve and new comparative genomics information emerges, the phylogenetic connections between species will change. Apparently, plant biologists have not yet solved the mystery of the origin of land plants.

Elk

Bryophytes are the group of plants that are the closest extant relatives of the earliest land plants. The first mosses (liver plants) probably appeared in the Ordovician, about 450 million years ago. Due to a lack of lignin and other strong structures, mosses are unlikely to form fossils. Some spores protected by sporopolenin survived and are attributed to the first mosses. In the Silurian, on the other hand, vascular plants spread across the continents. This compelling fact is used as evidence that nonvascular plants must have preceded the Silurian period.

More than 25,000 species of mosses thrive in moist habitats, although some live in deserts. They form the main flora of inhospitable environments such as the tundra, where their small size and tolerance to drought offer distinct advantages. They generally lack lignin and lack true tracheids (xylem cells specialized for transporting water). Instead, water and nutrients circulate in specialized conducting cells. Although the term non-tracheophyte is more accurate, bryophytes are commonly known as non-vascular plants.

In a moss, all conspicuous vegetative organs, including the photosynthetic leaf-like structures, the thallus, the stem, and the rhizoid that anchors the plant to its substrate, belong to the haploid organism, or gametophyte. The sporophyte is barely perceptible. Gametes formed by bryophytes swim with a flagellum, like the gametes of some tracheophytes. The sporangium, the multicellular sexual reproductive structure, is present in mosses and absent in most algae. The bryophyte embryo also remains attached to the mother plant, which protects and nourishes it. This is a characteristic of terrestrial plants.

Bryophytes are divided into three phyla: liverworts or hepaticophytes, tomentosum or anthocerotophytes, and bryophytes or true bryophytes.

hepatic

hepatic(Hepaticophyta) are considered the plants most closely related to the ancestor that migrated to earth. Liverworts have colonized all terrestrial habitats on Earth, diversifying into more than 7,000 extant species (Figure 9).

Some gametophytes form lobed green structures, as seen in Figure 10. The shape resembles liver lobes and thus provides the origin of the name given to the tribe. Openings can be seen in the livers that allow the movement of gases. However, these are not stomata as they do not actively open or close. The plant absorbs water on its entire surface and has no cuticle to prevent dehydration.

Figure 11 shows the life cycle of a liverwort. The cycle begins with the release of haploid spores from the sporangium that has developed into the sporophyte. The spores, dispersed by wind or water, germinate on flattened stalks attached to the substrate by thin unicellular filaments. The male and female gametangia develop on separate individual plants. After release, the male gametes swim to the female gametangium (archegonium) with the help of their flagella and fertilization occurs. The zygote grows into a small sporophyte that is still attached to the original gametophyte. It will produce the next generation of spores through meiosis. Liver plants can also reproduce asexually by breaking branches or spreading leaf fragments called shoots. In this latter playback mode, theexasperated- small intact pieces of whole plants produced in a cup on the stem surface (see Figure 11) - are splashed out of the cup by raindrops. The shoots then land nearby and develop into gametophytes.

sauerkraut

oanthocera(Anthocerotophyta) belong to the broad group of mosses. They have inhabited a variety of terrestrial habitats, although they are never far from a source of moisture. The short, bluish-green gametophyte is the dominant stage in the life cycle of a tomentosum. The narrow tubular sporophyte is the defining characteristic of the group. The sporophyte arises from the original gametophyte and continues to grow throughout the life of the plant (Figure 12).

Stomata occur on tomentosum and are abundant on the sporophyte. Photosynthetic thallus cells contain a single chloroplast. The meristematic cells at the base of the plant continue to divide and increase in height. Many tomentosum form symbiotic relationships with cyanobacteria, which sequester nitrogen from the environment.

The life cycle of tomentosum (Figure 13) follows the general pattern of alternation of generations. Gametophytes grow as flat stalks in the soil with embedded gametangia. The flagellated spermatozoa swim to the archegonia and fertilize the eggs. The zygote develops into a long, slender sporophyte that eventually splits open and releases spores. Thin cells called pseudoelaters surround the spores and help transport them further into the environment. Unlike the elaters found in horsetails, the pseudoelaters of the tomentosa are single-celled structures. The haploid spores germinate and give rise to the next generation of gametophytes.

Elk

More than 10,000 kinds ofElkthey were catalogued. Their habitats range from the tundra, where they are the primary vegetation, to the undergrowth of tropical forests. In the tundra, the flattened rhizoids of mosses allow them to adhere to a substrate without penetrating frozen ground. Mosses retard erosion, store soil moisture and nutrients, and provide shelter for small animals and food for larger herbivores such as musk oxen. Mosses are very sensitive to air pollution and are used to monitor air quality. They are also sensitive to copper salts, which is why these salts are a common ingredient in commercially available lawn moss removal compounds.

Mosses form tiny gametophytes, which are the dominant phase of the life cycle. The flat, green structures, similar to true leaves but lacking vascular tissue, are spirally connected to a central stem. Plants absorb water and nutrients directly through these leaf-like structures. Some mosses have small branches. Some primitive features of green algae, such as B. flagellated spermatozoa are still present in mosses that depend on water for reproduction. Other characteristics of mosses are clearly adaptations to the mainland. For example, stomata are present on sporophyte stems, and a primitive vasculature runs along the sporophyte stem. Furthermore, mosses are anchored in multiple cells in the subsoil, be it soil, rock, or tiles.rhizoid🇧🇷 These structures are precursors to roots. They originate from the base of the gametophyte but are not the main route for the absorption of water and minerals. The lack of a true root system explains why it's so easy to grow moss mats from a tree trunk. The moss life cycle follows the pattern of alternation of generations as shown in Figure 14.

The best known structure is the haploid gametophyte, which germinates from a haploid spore and initially aprotonema– usually a tangle of unicellular filaments hugging the ground. Cells resembling an apical meristem actively divide, giving rise to a gametophore composed of a photosynthetic stalk and sheet-like structures. Rhizoids form at the base of the gametophore. The gametangia of both sexes develop on separate gametophores. The male organ (the antheridium) produces many sperm, while the archegonium (the female organ) forms a single ovum. During fertilization, sperm travel down the throat to the uterus and join with the egg in the archegonia. Protected by the archegonium, the zygote divides and grows into a sporophyte that still has its foot attached to the gametophyte.

the thin oneseta(plural, bristles), as seen in Figure 15, contain tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium orhaircut.

A structure calledperistomioenhances spore reproduction after the capsule tip has fallen into the dispersal. The concentric tissue around the mouth of the capsule consists of close-fitting triangular units, a bit like "teeth"; These open and close depending on the humidity and regularly release spores.

Samenlose Gefäßpflanzen

vascular plants ortracheophyte, are the dominant and most conspicuous group of terrestrial plants. More than 260,000 species of tracheophytes represent more than 90% of the terrestrial vegetation. Several evolutionary innovations explain its success and ability to spread to all habitats.

Bryophytes may have made a successful transition from an aquatic habitat to land, but they still depend on water to reproduce, absorbing moisture and nutrients through the gametophyte surface. The lack of roots to absorb water and minerals from the soil, as well as the lack of reinforced conducting cells, limits bryophytes to small sizes. Although they can survive in reasonably dry conditions, they cannot reproduce and expand their habitat without water. Vascular plants, on the other hand, can reach enormous heights and thus successfully compete for light. Photosynthetic organs develop into leaves, and tubular cells or vascular tissues transport water, minerals, and fixed carbon throughout the organism.

In seedless vascular plants, the dominant stage of the life cycle is the diploid sporophyte. The gametophyte is now a discrete but still independent organism. Throughout the evolution of plants there is an apparent reversal of roles in the dominant phase of the life cycle. Seedless vascular plants still rely on water during fertilization because sperm must swim through a layer of moisture to reach the egg. This reproductive stage explains why ferns and their relatives are more common in humid environments.

Vascular tissues: xylem and phloem

The first fossils showing the presence of vascular tissue date from the Silurian period, about 430 million years ago. The simplest arrangement of conductor cells shows a pattern of xylem in the center surrounded by phloem.XilemaIt is the tissue responsible for the storage and transport of water and nutrients over long distances, as well as for the transfer of water-soluble growth factors from the organs of synthesis to the target organs. The tissue is made up of conducting cells known as tracheids and a supporting filler tissue called parenchyma. The conducting cells of the xylem pick up the connection.ligninon its walls and are therefore called lignified. Lignin itself is a complex polymer that is impermeable to water and provides mechanical strength to vascular tissue. With their rigid cell walls, the xylem cells support the plant and allow it to reach impressive heights. Tall plants have a selective advantage, as they can reach unfiltered sunlight and further disperse their spores or seeds, expanding their range. By growing larger than other plants, tall trees shade shorter plants and limit competition for valuable water and nutrients in the soil.

Bastit is the second type of vascular tissue; it transports sugars, proteins, and other solutes throughout the plant. Phloem cells are divided into sieve elements (conductor cells) and cells that carry the sieve elements. Together, the xylem and phloem tissues form the vasculature of plants.

Roots: support for the plant

The roots are not well preserved in the fossil record. However, it seems that the roots appeared later in evolution than the vascular tissues. The development of an extensive network of roots represented a great innovation in vascular plants. Fine rhizoids attached the bryophytes to the substrate, but these rather fragile filaments did not provide the plant with a strong anchorage; They also did not absorb significant amounts of water and nutrients. Rather, the roots, with their extensive system of vascular tissue, transfer water and minerals from the soil to the rest of the plant. The extensive root network, which penetrates deep into the soil to reach water sources, further stabilizes the trees and acts as a ballast or anchor. Most roots form a symbiotic relationship with fungi, forming mycorrhizae that benefit the plant by greatly increasing the surface area for absorbing water, minerals, and nutrients from the soil.

Leaves, sporophylls and strobila

A third innovation introduces seedless vascular plants. Along with the prominence of the sporophyte and the development of vascular tissue, the appearance of true leaves enhanced their photosynthetic efficiency. With their increased surface area, the leaves capture more sunlight and use more chloroplasts to capture and convert light energy into chemical energy, which is then used to convert atmospheric carbon dioxide into carbohydrates. Carbohydrates are exported to the rest of the plant by directing cells in the phloem tissue.

The existence of two types of morphology suggests that the leaves of different groups of plants evolved independently. The first type of leaf is theMicrofilo, or "little leaf", which can be dated to 350 million years at the end of the Silurian. A microphyll is small and has a simple vasculature. A single unbranchedsah- a bundle of vascular tissue made up of xylem and phloem - runs down the center of the leaf. Microphylls may come from flattened lateral branches or from sporangia that have lost their ability to reproduce. Microphylls are present in mosses and probably predate development.megaphileor "big leaves", which are larger leaves with a pattern of branching veins. Megaphiles probably appeared independently several times throughout evolution. Its complex networks of veins suggest that multiple branches may have joined to form a flattened organ, with the spaces between the branches filled with photosynthetic tissue.

In addition to photosynthesis, leaves play another role in plant life. Pine cones, mature fern leaves, and flowers are allsporophile– Leaves structurally modified to support sporangia.EstrobiliThey are cone-shaped structures that contain sporangia. They are prominent in conifers and are commonly known as pine cones.

Ferns and other seedless vascular plants

By the end of the Devonian period, plants had developed vascular tissues, well-defined leaves, and root systems. With these benefits, the plants increased in height and size. During the Carboniferous period, swamp forests of mosses and horsetail (some specimens reaching more than 30 m (100 ft) in height) covered most of the country. From these forests arose the extensive coal deposits that gave the Carboniferous its name. In seedless vascular plants, the sporophyte has become the dominant phase of the life cycle.

Seedless vascular plants still require water for fertilization and most prefer a moist environment. Modern seedless tracheophytes include mosses, horsetails, ferns, and ferns.

Filo Lycopodiophyta: Clubmoss

oElk, the tribeLycopodiophyta, are the first group of seedless vascular plants. They dominated the Carboniferous landscape, growing into tall trees and forming large swamp forests. Modern club mosses are small perennial plants composed of a stem (which can branch) and microphylls (Figure 17). The phylum Lycopodiophyta consists of about 1,200 species, including the prickly pear (isoetais), die moose (Lykopodien) and spiny mosses (Elfzehn), neither of which are true mosses or bryophytes.

Lycophytes follow the pattern of alternation of generations observed in bryophytes, except that the sporophyte is the main stage of the life cycle. Gametophytes do not depend on the sporophyte for nutrients. Some gametophytes develop underground and form mycorrhizal associations with fungi. In clubmoss, the sporophyte gives rise to sporophylls, which are organized into strobila, conical structures that give the class its name. Lycophytes can be homosporous or heterosporous.

Phylum Monilophyta: Class Equisetopsida (Cola de Caballo)

Horsetails, ferns, and tree ferns belong to the phylum Monilophyta, withhorse tailplaced in the class Equisetopsida. the only genderEquisetumIt is the survivor of a large group of plants known as the Arthrophyta, which gave rise to large trees and entire swampy forests in the Carboniferous. Plants are generally found in wet, swampy environments (Figure 18).

The horsetail stem is characterized by the presence of joints or nodes, hence the name Arthrophyta (Arthritis– = „Junta“; –salida= "plant"). Leaves and branches spiral out of evenly spaced joints. The needle-shaped leaves do not contribute much to photosynthesis, most of which takes place on the green stem (Figure 19).

Silica accumulates in epidermal cells and contributes to the stiffness of horsetail plants. Underground stems, known as rhizomes, anchor plants to the soil. Modern horsetails are homosporous and produce bisexual gametophytes.

Phylo Monilophyta: Class Psilotopsids

While most ferns form large leaves and branching roots, they are fernsbeat ferns, class Psilotopsida, without roots or leaves, probably lost by reduction. Photosynthesis takes place on their green stems, and small yellow bumps containing the sporangia form at the tip of the branch stem. Ferns were considered one of the first pterophytes. However, recent comparative DNA analysis suggests that this clade may have lost vascular tissue and roots during evolution and is more closely related to ferns.

Filo Monilophyta: Klasse Psilotopsida (Samambaias)

with its big leavesdo somethingthey are the most easily recognizable seedless vascular plants. They are considered the most advanced seedless vascular plants and have characteristics commonly seen in seed plants. More than 20,000 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, shady locations. Ferns appeared in the fossil record during the Devonian period and spread during the Carboniferous.

The predominant stage in a fern's life cycle is the sporophyte, consisting of large compound leaves called fronds. The fronds do double duty; 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 can grow above the ground like a stem in ferns (Figure 21).CoincidentallyOrgans are those that grow in unusual places, like roots growing from side to side of a trunk.

The tip of a developing fern leaf wraps around a cane or fiddle head (Figure 22). Fiddleheads unfurl as the foliage develops.

The life cycle of a fern is shown in Figure 23.

To see an animation of the life cycle of a fern and test your knowledge, go towebsite.

Most ferns produce the same type of spores and are therefore homosporous. The diploid sporophyte is the most obvious stage of the life cycle. On the underside of its mature leaves, the sori (singular, sorus) form small clusters in which the sporangia develop (Figure 24).

Within the sera, the spores are produced by meiosis and released into the air. Those that land on a suitable substrate germinate and form a heart-shaped gametophyte attached to the soil by thin filamentous rhizoids (Figure 25).

The discrete gametophyte harbors both sexual gametangia. Flagellated sperm released from the antheridium swim across a moist surface to the archegonia, where the ovum is fertilized. The newly formed zygote becomes a sporophyte, which arises from the gametophyte and grows through mitosis into the next generation sporophyte.

The importance of seedless vascular plants

Mosses and liverworts are often the first macroscopic organisms to colonize an area, both in primary succession, where bare soil is colonized first by living organisms, and in secondary succession, where the soil remains intact after a disaster, decimating many species. existing. Its spores are carried by the wind, birds or insects. Once established, mosses and liverworts provide food and shelter for other species. In a harsh environment like the tundra, where the ground is frozen, bryophytes grow well because they have no roots and can dry out quickly and rehydrate when water becomes available again. Mosses are 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. Predators, in turn, feed on herbivores, which are the main consumers. Some reports suggest that mosses make the soil more conducive to colonization by other plants. By establishing symbiotic relationships with nitrogen-fixing cyanobacteria, mosses replenish the soil with nitrogen.

In the late 19th century, scientists noticed that lichens and mosses were becoming rarer in urban and suburban areas. Because mosses do not have a root system to absorb water and nutrients, nor a cuticle layer to protect them from drying out, contaminants from rainwater easily penetrate their tissues. They absorb moisture and nutrients through all their exposed surfaces. Therefore, dissolved pollutants in rainwater easily penetrate plant tissues and affect mosses more than other plants. The disappearance of mosses can be seen as a bioindicator of the level of environmental contamination.

Ferns contribute to the environment by promoting rock erosion, accelerating topsoil formation, and slowing erosion by spreading rhizomes into the soil. The aquatic ferns of the genusazollathey harbor nitrogen-fixing cyanobacteria and return this important nutrient to aquatic habitats.

Historically, seedless plants have played an important role in human life, being used as tools, fuel, and medicine. Driedtorfmoos,Esfagno, is widely used as a fuel in some parts of Europe and is considered a renewable resource.EsfagnoThe bogs (Figure 27) are cultivated with bramble and blueberry bushes. The ability toEsfagnoto retain moisture, moss is a common soil conditioner. Florists use blocks ofEsfagnoto maintain humidity in floral arrangements.

The attractive fronds of ferns make them a popular ornamental plant. Because they thrive in low light, they are suitable as houseplants. More importantly, fiddleheads are a traditional Native American spring food in the Pacific Northwest and are popular as a garnish in French cuisine. liquorice fern,Polypodium glicirriza,It is part of the diet of the coastal tribes of the Pacific Northwest, partly due to the sweetness of its rhizomes. It has a slight licorice flavor and serves as a sweetener. The rhizome is also listed in the Native American Pharmacopoeia for its medicinal properties and is used as a sore throat remedy.

yours iswebsiteto learn how to identify fern species by their fiddle heads.

However, by far the greatest impact on human life comes from their extinct ancestors. The tall mosses, horsetails, and tree ferns that flourished in Carboniferous swamp forests gave rise to vast coal deposits around the world. Coal was an abundant source of energy during the Industrial Revolution, which had tremendous consequences for human society, including rapid technological advances and the growth of large cities, as well as environmental degradation. Coal remains a primary source of energy and also a major contributor to global warming.

check your understanding

Please answer the following questions to determine your understanding of the topics discussed in the previous section. this little quizNocounts towards your class grade and can be replayed an unlimited number of times.

Use this quiz to check your understanding and decide if you want to (1) continue studying the previous section or (2) move on to the next section.