Psilophytes are the firstborn of terrestrial vegetation. Origin and evolution of land plants

Origin and evolution of land plants

In the Proterozoic, the land was inhabited by prokaryotes; single-celled eukaryotes joined them later (about 1 billion years ago). The first inhabitants of land were probably cyanobacteria and actinobacteria. Heterotrophic actinobacteria form numerous branching structures similar to fungal mycelium. They are able to unite with phototrophic cyanobacteria into amazing symbiotic “superorganisms” (the so-called actinolichens).

Perhaps the most important evolutionary event in the Phanerozoic was the colonization of land by multicellular eukaryotes. As a result, landscapes familiar to us emerged, dominated by terrestrial plants, insects and four-legged animals (tetrapods).

Phylogenetic reconstructions based on comparisons of the genomes of modern organisms indicate that land plants originated from charophyte algae. Representatives of this group of freshwater green algae include both unicellular and multicellular forms. Apparently, one of the transitions to multicellularity about 1 billion years ago occurred during the evolution of charophyte algae. To date, no fossil remains of transitional forms between land plants and their aquatic ancestors are known.

The main problems that aquatic plants face when reaching land, and their solutions. Drying (solution - integumentary tissues or falling into suspended animation in bryophytes), the need for gas exchange and evaporation (stomata), absorption of substances (absorbent tissues, mycorrhiza), transport of substances (conductive tissues - except bryophytes), competition, gravity (mechanical tissues).

Among the first inhabitants of land were mushrooms, which also entered into symbiosis with cyanobacteria. The genetic and biochemical systems that land fungi developed for symbiosis with cyanobacteria later came in handy for them to “establish relationships” with the first land plants. All this terrestrial microbiota gradually prepared the ground (literally and figuratively) for the colonization of land by plants. From the very beginning, land plants lived in close symbiosis with soil fungi, without which they most likely would not have been able to leave their native water element.

The oldest fossil land plants are fragments of liver moss containing spores (about 460 million years ago). According to phylogenetic reconstructions, this group of mosses is the most ancient land plants. Vascular plants (all terrestrial plants, except bryophytes) arose during evolution no later than 420 million years ago. Within this group, two evolutionary lines are distinguished. In spore plants (horsetails, mosses and ferns, which arose no later than 350 million years ago), both the sporophyte and the gametophyte are independent organisms. In seed plants, the haploid gametophyte has lost its independence. Spore-bearing plants (rhiniophytes) were the first to reach land - this happened at the end of the Silurian. They grew in shallow coastal waters; they did not have real roots; special thread-like processes served to attach to the substrate.

Towards the end of the Devonian period, the first forests began to appear. They consisted of spore-bearing plants - ferns, club mosses, and horsetails. In carbon(Carboniferous period) significant warming and humidification of the climate provided wide use tropical forests (Europe, North America, South Asia - then these territories were located in the equatorial belt), formed by tree ferns, giant tree-like horsetails and mosses (up to 40 m in height). These forests, located in the coastal lowlands, have no modern analogues. These were shallow reservoirs overflowing with organic remains. The root systems of the trees were located below the peat-like organic mass, and the trunks grew through it and a thick layer of dead wood. It was on the site of these “forest-reservoirs” that large coal basins subsequently arose.

On the territory of modern Siberia and Far East, which were then located near the Arctic Circle, the basis of the vegetation consisted of coniferous trees up to 20 m high (cordites). Their wood has clear growth rings, confirming the existence of a seasonal climate there (something like modern taiga). Territories of modern South America and Africa (their southern halves), India and Australia were then located near the southern polar circle. It was dominated by deciduous ginkgo forests.

In the Carboniferous appeared and first gymnosperms(a collective group called "seed ferns"). Their seed was covered with a shell that protected it from drying out. Reproduction using seeds made the reproduction process independent of the aquatic environment. This aromorphosis made it possible to further develop the land and move plants deeper into the continents.

In the colder and drier Permian period, gymnosperms became widespread. Of these, only a few have survived to this day - gingkos, araucarias, and cycads.

The oldest reliable finds of angiosperms (flowering) plants are 140-130 million years old; these are single pollen grains found in Israel. The earliest macroscopic fossils (leaves, flowers, fruits) of angiosperms are about 125 million years old. Since they are already quite diverse, angiosperms apparently arose much earlier (they separated from gymnosperms no later than 300 million years ago). Compared to gymnosperms, angiosperms experienced an important aromorphosis - double fertilization appeared, which prevented the waste of nutrients (endosperm develops only together with the embryo), the ovary performs protective function. The evolutionary success of angiosperms is explained by their short life cycle, propensity for insect pollination, and the formation of a variety of herbaceous forms. Some of the angiosperms that arose in the Cretaceous period have survived to this day - these are palm trees and plane trees.

There are now hundreds of thousands of species of flowering plants on Earth, and the phylogenetic relationships between them are quite well studied. An important role in the emergence modern diversity flowering plants played a role in their co-evolution with insects.

Multicellular animals and land plants are the only two known cases occurrence of multi-tissue, which led to the emergence of complex large organisms. Interestingly, the genetic mechanisms of these two independent events very similar. First, the emergence of a complex multicellular organism was not accompanied by a significant increase in the number of protein-coding genes. Instead, the interactions between genes and their regulatory elements - special DNA sequences - became more complex. Secondly, animals and plants have independently evolved special genes that regulate the individual development of the organism.

The monograph is devoted to the consideration of the most complex problem in botany of the origin and evolution of bryophytes - unique two-pronged higher plants of the gametophytic direction of development. The development of this problem is based on logical modeling using the comparative morphological method as the leading tool of cognition. Based on the analysis of materials concerning the organization of bryophytes from the molecular to the organ level, taking into account existing ideas on this problem, the author has developed a holistic conceptual model of the origin and evolution of bryophytes, starting from the algae-like ancestors of the archegoniates. Particular attention is paid to Anthocerotaceae and Takakiaceae as the oldest terrestrial plants, a kind of “living fossil” - key taxa for understanding the initial stage of the evolution of embryophytes.
Intended for wide range specialists in the field of botany, ecology, geography, students and teachers of biological universities and everyone interested in the evolution of higher plants.

Algae as ancestral forms of archegoniates.
Due to the fact that bryophytes show much greater similarity with tracheophytes than with algae, possessing virtually all the main characteristics of higher plants, first of all we should touch upon the possible routes of origin of the latter as a whole as a new level of organization in the development of the plant world.

The emergence of higher plants (archegoniates, or embryophytes) marked important stage progressive, progressive development of plants, their entry into a fundamentally new ecological arena, the development of a much more complex, integrated terrestrial environment, a vivid manifestation of the spreading of living matter across the planet, the “everywhereness” of life (in the apt expression of V.I. Vernadsky, 1960). From here it clearly follows that the evolution of organisms is essentially adaptationogenesis.

In developing the problem of the origin of higher plants, comprehensive studies of both various groups of higher plants and algae, which are considered as the ancestors of archegoniates, are important.

To date, significant progress has been made in the study of algae, including their modern and fossil forms. In particular, the works of K. D. Stewart, K. R. Mattox (1975, 1977, 1978), K. J. Niklas (1976), L. E. Graham (1984, 1985), Yu. E. Petrova attract attention (1986) and others.

CONTENT
Preface
Evolution Research Methodology
Evolutionary theory
Current state evolutionary doctrine
Ideas about the basic laws of evolution
Origin of higher plants
Algae as ancestral forms of archegoniates
Change of nuclear phases (development cycle of higher plants)
Apomixis and its role in the evolution of higher plants. The concept of “generation” in relation to embryophytes
Possible cytological certainty of ancestral forms of higher plants
Predecessors of higher plants and their transformation into primary archegoniates
Ecological situation when the initial forms of higher plants reached land
The emergence of embryophyty
Transformation of chloroplasts during the emergence of higher plants
The oldest land plants. Transitional forms between algae and higher plants. Rhiniophytes
Pathways of transformation of early land plants
Origin and evolution of the main groups of bryophytes
Antocerotophyta
The uniqueness of the group organization as a reason for the uncertainty of its phylogenetic position and genetic relationships
Fossil plants exhibiting features similar to Anthocerotes, and their comparative analysis
Ancestral form of anthocerotes
Features of analogy of Anthocerotes with other higher plants and adaptation genesis of this group of bryophytes
Liverworts (Marchantiophyta)
The oldest fossil forms of liverworts
Liverworts as the “least terrestrial” organisms among bryophytes
Initial ecological conditionality of liverworts
Historical relationships between the leaf-stem and thallus morphotypes of the gametophyte
Changes in the structure of the sporogon in the Lower-Middle Devonian
Late Devonian-Early Carboniferous evolution of the liverwort gametophyte
Protonema (seedling), its significance in the development cycle and transformation
Transformation of the structure of the sporogon in the Upper Devonian
Evolution of liverworts in the Carboniferous
Initial morphotype of bryophyte gametophyte
Symmetry in the morphogenesis of liverworts in connection with their lifestyle
Divergence of the liverwort division
Signs of organization of ferns as a means of understanding the development paths of bryophytes
Features of the organization of Jungermannian liverworts (Jungermanniophytina)
Organization of Marchantiophytina as a consequence
their specific ecology. Group divergence
Oil bodies and their dislocation in liverworts
Taxa with mixed characters of the two main groups of liverworts and models of the origin of these groups
Time of appearance of modern families and genera of liverworts
Newest classification of liverworts
Mosses (Bryophyta)
Specifics of group organization
Ancient fossil mosses
The nature of the relationship between mosses and liverworts
The highest degree of terrestriality of mosses among bryophytes
Restoration of the process of formation of the main morphotype of mosses
Comparative morphological series of sporogons as a model of their changes during the evolution of mosses
Takakiophytina
Mosses proper (Bryophytina)
Sphagnum mosses (Sphagnopsida)
Andrew's mosses (Andreaeopsida)
Lndreobryopsida mosses (Andreaeobryopsida)
Bryopsida
Changes in the basic number of chromosomes in bryophytes during their evolution
Bryophytes in the Paleocene and Eocene
Impact of climate change on bryophytes in the Oligocene and Neogene
Bryophytes under severe anthropogenic stress
Ecological inversions of bryophytes
Forecast of the evolution of bryophytes in connection with natural and anthropogenic changes in the biosphere
Phylogenetic relationships between the largest taxa of bryophytes, as well as between bryophytes and other higher plants
Conclusion
Overview of the evolution of bryophytes according to the conceptual model suggested by us (summary)
Literature.

To substantiate the theory of evolution, Charles Darwin widely used numerous evidence from the fields of paleontology, biogeography, and morphology. Subsequently, facts were obtained recreating the history of development organic world and serving as new evidence of the unity of origin of living organisms and the variability of species in nature.

Paleontological finds - perhaps the most convincing evidence of the evolutionary process. These include fossils, imprints, fossil remains, fossil transitional forms, phylogenetic series, sequence of fossil forms. Let's take a closer look at some of them.

1. Fossil transitional forms- forms of organisms that combine the characteristics of older and younger groups.

Of particular interest among plants are psilophytes. They originated from algae, were the first of the plants to make the transition to land and gave rise to higher spore and seed plants. Seed ferns - a transitional form between ferns and gymnosperms, and cycads - between gymnosperms and angiosperms.

Among fossil vertebrates, one can distinguish forms that are transitional between all classes of this subtype. For example, the oldest group lobe-finned fish gave rise to the first amphibians - stegocephalus (Fig. 3.15, 3.16). This was possible due to the characteristic structure of the skeleton of the paired fins of lobe-finned fish, which had the anatomical prerequisites for their transformation into the five-fingered limbs of primary amphibians. Forms are known that form the transition between reptiles and mammals. These include beast lizards (foreigner disease) (Fig. 3.17). And the connecting link between reptiles and birds was per-bird (Archaeopteryx) (Fig. 3.18).

The presence of transitional forms proves the existence of phylogenetic connections between modern and extinct organisms and helps in building a natural system and family tree of the flora and fauna.

2. Paleontological series- series of fossil forms related to each other in the process of evolution and reflecting the course of phylogenesis (from the Greek. phylon- clan, tribe, genesis- origin). A classic example of the use of series of fossil forms to elucidate the history of a particular group of animals is the evolution of the horse. Russian scientist V.O. Kovalevsky (1842-1883) showed the gradual evolution of the horse, establishing that successive fossil forms became increasingly similar to modern ones (Fig. 3.20).

Modern one-toed animals descended from small five-toed ancestors who lived in forests 60-70 million years ago. Climate change has led to an increase in the area of ​​steppes and the spread of horses across them. Movement over long distances in search of food and protection from predators contributed to the transformation of the limbs. At the same time, the size of the body and jaws increased, the structure of the teeth became more complex, etc.

To date, a sufficient number of paleontological series are known (proboscis, carnivores, cetaceans, rhinoceroses, some groups of invertebrates), which prove the existence of an evolutionary process and the possibility of the origin of one species from another.

Morphological evidence are based on the principle: the deep internal similarity of organisms can show the relationship of the compared forms, therefore, the greater the similarity, the closer their relationship.

1. Homology of organs. Organs that have a similar structure and common origin are called homologous. They occupy the same position in the animal’s body, develop from similar rudiments and have the same structural plan. A typical example of homology is the limbs of terrestrial vertebrates (Fig. 3.21). Thus, the skeleton of their free forelimbs necessarily has a humerus, a forearm, consisting of the radius and ulna, and a hand (wrist, metacarpus and phalanges of the fingers). The same pattern of homology is observed when comparing the skeleton of the hind limbs. In the horse, the stylus bones are homologous to the metacarpal bones of the second and fourth fingers of other ungulates. It is obvious that in the modern horse these toes have disappeared during the process of evolution.

It has been proven that the poisonous glands of snakes are a homologue of the salivary glands of other animals, the sting of a bee is a homologue of the ovipositor, and the sucking proboscis of butterflies is a homologue of the lower pair of jaws of other insects.

Plants also have homologous organs. For example, pea tendrils, cactus and barberry spines are modified leaves.

Establishing the homology of organs allows us to find the degree of relationship between organisms.

2. Analogy.Similar bodies - these are organs that are externally similar and perform the same functions, but have different origins. These organs indicate only a similar direction of adaptation of organisms, determined in

the process of evolution through the action of natural selection. The external gills of tadpoles, the gills of fish, polychaete annelids, and aquatic insect larvae (such as dragonflies) are similar. Walrus tusks (modified fangs) and elephant tusks (overgrown incisors) are typical analogous organs, since their functions are similar. In plants, barberry spines (modified leaves), white acacia spines (modified stipules) and rose hips (develop from bark cells) are similar.

Rudiments.Vestigial (from lat. rudimentum- rudiment, primary basis) are organs that are formed during embryonic development, but later stop developing and remain in adult forms in an underdeveloped state.

In other words, rudiments are organs that have lost their functions. Rudiments are the most valuable evidence of the historical development of the organic world and the common origin of living forms. For example, anteaters have rudimentary teeth, humans have ear muscles, skin muscles, the third eyelid, and snakes have limbs (Fig. 3.22). Atavisms. (from lat. The appearance in individual organisms of any type of characteristics that existed in distant ancestors, but were lost during evolution, is called atavism

atavus - ancestor). In humans, atavisms are the tail, hair on the entire surface of the body, and multiple nipples (Fig. 3.23). Among thousands of one-toed horses, there are specimens with three-toed limbs. Atavisms do not carry any functions important for the species, but show the historical relationship between extinct and currently existing related forms. Embryological proof stva. In the first half of the 19th century. Russian embryologist K.M. Baer (1792-1876) formulated the law of germinal similarity: the earlier the stages

For example, in the early stages of development, vertebrate embryos do not differ from each other. Only at the middle stages do features characteristic of fish and amphibians appear, and at later stages do features of the development of reptiles, birds and mammals appear (Fig. 3.24). This pattern in the development of embryos indicates the relationship and sequence of divergences in the evolution of these groups of animals.

The deep connection between the individual and the historical is expressed in biogenetic law, established in the second half of the 19th century. German scientists E. Haeckel (1834-1919) and F. Müller (1821-1897). According to this law, each individual in its individual development (ontogenesis) repeats the history of the development of its species, or ontogenesis is short

and rapid repetition of phylogeny. For example, in all vertebrates, a notochord is formed during ontogenesis, a feature that was characteristic of their distant ancestors. The tadpoles of tailless amphibians develop a tail, which is a repetition of the characteristics of their tailed ancestors.

Subsequently, amendments and additions were made to the biogenetic law. A special contribution to elucidating the connections between onto- and phylogeny was made by the Russian scientist A.N. Severtsov (1866-1936).

It is clear that in such a short period of time as individual development, all stages of evolution cannot be repeated. Therefore, repetition of stages historical development species in embryonic development occurs in a compressed form, with the loss of many stages. At the same time, the embryos of organisms of one species are similar not to the adult forms of another species, but to their embryos. Thus, the gill slits in a one-month-old human embryo are similar to those in a fish embryo, but not in an adult fish. This means that during ontogenesis, mammals go through stages similar to fish embryos, and not to adult fish.

It should be noted that Charles Darwin drew attention to the phenomenon of repetition in ontogenesis of the structural features of ancestral forms.

All of the above information is of great importance for proving evolution and for elucidating related relationships between organisms.

Biogeographic evidence. Biogeography is the science of the patterns of modern settlement of animals and plants on Earth.

You already know from the physical geography course that modern geographic zones were formed during the historical development of the Earth, as a result of the action of climatic and geological factors. You also know that often similar natural zones turn out to be inhabited by different organisms, and different zones are similar. Explanations for these facts can only be found from the standpoint of evolution. For example, the originality of the flora and fauna of Australia is explained by its isolation in the distant past, and therefore the development of the animal and plant world occurred in isolation from other continents. Consequently, biogeography contributes much evidence to the evolution of the organic world.

Currently, methods of biochemistry and molecular biology, genetics, and immunology are widely used to prove evolutionary processes.

Thus, by studying the composition and sequence of nucleotides in nucleic acids and amino acids in proteins in different groups of organisms and detecting similarities, one can judge their relationship.

Biochemistry has research methods that can be used to determine the “blood relationship” of organisms. When comparing blood proteins, the ability of organisms to produce antibodies in response to the introduction of foreign proteins into the blood is taken into account. These antibodies can be isolated from blood serum and determined at what dilution this serum will react with the serum of the comparison organism. This analysis showed that the closest relatives of humans are the great apes, and the most distant of them are lemurs.

The evolution of the organic world on Earth is confirmed by many facts from all areas of biology: paleontology (phylogenetic series, transitional forms), morphology (homology, analogy, rudiments, atavisms), embryology (law of embryonic similarity, biogenetic law), biogeography, etc.

The emergence of unicellular and multicellular algae, the emergence of photosynthesis: the emergence of plants on land (psilophytes, mosses, ferns, gymnosperms, angiosperms).

The development of the plant world took place in 2 stages and is associated with the appearance of lower and higher plants. According to the new taxonomy, algae are classified as lower (and previously included bacteria, fungi and lichens. Now they are separated into independent kingdoms), and mosses, pteridophytes, gymnosperms and angiosperms are classified as higher.

In the evolution of lower organisms, two periods are distinguished, which differ significantly in the organization of the cell. During period 1, organisms similar to bacteria and blue-green algae dominated. The cells of these life forms did not have typical organelles (mitochondiria, chloroplasts, Golgi apparatus, etc.). The cell nucleus was not limited by the nuclear membrane (this is a prokaryotic type of cellular organization). Period 2 was associated with the transition of lower plants (algae) to an autotrophic type of nutrition and with the formation of a cell with all the typical organelles (this is a eukaryotic type of cellular organization, which was preserved at subsequent stages of development of the plant and animal world). This period can be called the period of dominance of green algae, unicellular, colonial and multicellular. The simplest of multicellular organisms are filamentous algae (ulotrix), which do not have any branching in their body. Their body is long chain consisting of individual cells. Other multicellular algae are dismembered big amount outgrowths, so their body branches (in Hara, in Fucus).

Multicellular algae, due to their autotrophic (photosynthetic) activity, developed in the direction of increasing body surface for better absorption of nutrients from the aquatic environment and solar energy. Algae have a more progressive form of reproduction - sexual reproduction, in which a new generation begins with a diploid (2n) zygote, combining the heredity of 2 parental forms.

The 2nd evolutionary stage of plant development must be associated with their gradual transition from an aquatic to a terrestrial lifestyle. The primary terrestrial organisms turned out to be psilophytes, which were preserved as fossil remains in Silurian and Devonian deposits. The structure of these plants is more complex compared to algae: a) they had special bodies attachment to the substrate - rhizoids; b) stem-like organs with wood surrounded by phloem; c) rudiments of conducting tissues; d) epidermis with stomata.

Starting with psilophytes, it is necessary to trace 2 lines of evolution of higher plants, one of which is represented by bryophytes, and the second by ferns, gymnosperms and angiosperms.

The main thing that characterizes bryophytes is the predominance of the gametophyte over the sporophyte in their individual development cycle. A gametophyte is an entire green plant capable of self-feeding. The sporophyte is represented by a capsule (cuckoo flax) and is completely dependent on the gametophyte for its nutrition. The dominance of the moisture-loving gametophyte in mosses under the conditions of an air-terrestrial lifestyle turned out to be impractical, so mosses became a special branch of the evolution of higher plants and have not yet given rise to perfect groups of plants. This was also facilitated by the fact that the gametophyte, compared to the sporophyte, had poor heredity (haploid (1n) set of chromosomes). This line in the evolution of higher plants is called gametophytic.

The second line of evolution on the path from psilophytes to angiosperms is sporophytic, because in ferns, gymnosperms and angiosperms the sporophyte dominates in the cycle of individual plant development. It is a plant with a root, stem, leaves, sporulation organs (in ferns) or fruiting organs (in angiosperms). Sporophyte cells have a diploid set of chromosomes, because they develop from a diploid zygote. The gametophyte is greatly reduced and is adapted only for the formation of male and female germ cells. In flowering plants, the female gametophyte is represented by the embryo sac, which contains the egg. The male gametophyte is formed when pollen germinates. It consists of one vegetative and one generative cell. When pollen germinates, 2 sperm arise from the generative cell. These 2 male reproductive cells are involved in double fertilization in angiosperms. The fertilized egg gives rise to a new generation of the plant - the sporophyte. The progress of angiosperms is due to the improvement of the reproductive function.

Plant groups Signs of increasing complexity of plant organization (aromorphoses) 1. Algae The appearance of chlorophyll, the emergence of photosynthesis, multicellularity. 2. Psilophytes as a transitional form Special organs of attachment to the substrate are rhizoids; stem organs with rudiments of conducting tissues; epidermis with stomata. 3. Mosses The appearance of leaves and stems, tissues that provide the possibility of life in a terrestrial environment. 4. Ferns The appearance of real roots, and in the stem - tissues that ensure the conduction of water absorbed by the roots from the soil. 5. Gymnosperms The appearance of the seed is internal fertilization, the development of the embryo inside the ovule. 6. Angiosperms The appearance of a flower, the development of seeds inside the fruit. Diversity of roots, stems, leaves in structure and functions. Development of a conducting system that ensures the rapid movement of substances in the plant.

Conclusions:

1. The study of the geological past of the Earth, the structure and composition of the core and all shells, spacecraft flights to the Moon, Venus, and the study of stars brings a person closer to understanding the stages of development of our planet and life on it.
2. The process of evolution was natural.
3. The plant world is diverse, this diversity is the result of its development over a long time. The reason for its development is not divine power, but the change and complication of the structure of plants under the influence of changing environmental conditions.

Scientific evidence: cellular structure plants, the beginning of development from one fertilized cell, the need for water for life processes, the finding of imprints of various plants, the presence of “living” fossils, the extinction of some species and the formation of new ones.