1 ground plants. The first land plants. Origin and taxonomy of higher plants

In this article we will discuss an important and interesting topic - the emergence and development of the plant world on the planet. Today, walking in the park during the lilac bloom, picking mushrooms in the autumn forest, watering home flowers on the windowsill, insisting on a decoction of chamomile during an illness, we rarely think about how the Earth looked before the advent of plants. What was the landscape like at the time when single-celled plants were just emerging or the first weak land plants appeared? What did forests look like in the Paleozoic and Mesozoic? Imagine that the ancestors of those half-meter ferns, which now modestly hide in the shade of fir trees, reached a height of 30 meters or more 300 million years ago!

Let's list the main stages of the emergence of the living world.

The origin of life

1. 3, 7 billion years ago arose first living organisms. The time of their appearance (very approximately, with a "fork" of hundreds of millions of years) today can be assumed from the deposits formed by them. For a million plus years cyanobacteria have learned oxygen photosynthesis and so bred that they became the culprits of the oversaturation of the atmosphere with oxygen about 2.4 billion years ago - this led to the extinction of anaerobic organisms, for which oxygen was a poison. The living world of the Earth has changed radically!

2. 2 billionyears ago there were already different unicellular both autotrophs and heterotrophs. These p first unicellular did not have nuclei and plastids - the so-called heterotrophic prokaryotes (bacteria). It was they who gavethe impetus for the appearance of the first unicellular plants.

3. 1, 8 billionyears ago, nuclear unicellular organisms arose,that is, eukaryotes, soon (by geological standards)typical animal and plant cells appeared.

The emergence of multicellular plants

1. Near 1, 2 billion years back on the basis of unicellular originatedmulticellular algae.

2. At that time, life existed only in warm seas and oceans, but living organisms actively developed and progressed - they were preparing for the development of land.

Exit of plants to land

1. 4 20 millionyears ago, the first land plants appeared - mosses and psilophytes (rhinophytes). They originated in many places on the planet.independently of each other, from different multicellular algae.Of course, at first they mastered only the coastal edge.

2. psilophytes(for example, riniya) lived along the banks, in shallow water, like modern m sedges. These were small weak plants, whose life was complicated by the lack of shoots and roots.. Instead of roots that can properly cling to the soil, psilophytes had rhizoids. The upper part of the psilophyte contained a green pigment and was capable of photosynthesis. These pioneers, bold invaders of land, have died out,but were able to give rise to ferns.

4. mosses - for all their unusualness, beauty and ubiquity in our days - have become a dead end branch of evolution. Having arisen hundreds of millions of years ago, they could not give rise to any other groups of plants.

Question 1. When did the first land plants appear? What were they called and what distinguishing features did they have?

At the beginning of the Paleozoic era (the era of ancient life), plants inhabit mainly the seas, but after 150-170 million years, the first terrestrial plants appear - psilophytes, occupying an intermediate position between algae and terrestrial vascular plants. Psilophytes already had poorly differentiated tissues capable of carrying water and organic substances, and could strengthen themselves in the soil, although they still lacked true roots (as well as true shoots). Such plants could exist only in a humid climate; when arid conditions were established, the psilophytes disappeared. However, they gave rise to more adapted land plants.

Question 2. In what direction was the evolution of plants on land?

Further evolution of plants on land went in the direction of dismembering the body into vegetative organs and tissues, improving the vascular system (ensuring the rapid movement of water to a great height). Spore plants (horsetails, club mosses, ferns) are widely distributed.

Question 3. What evolutionary advantages does the transition of plants to seed reproduction give?

The transition to seed reproduction gave plants many advantages: the embryo in the seed is now protected from adverse conditions by shells and provided with food. In some gymnosperms (conifers), the process of sexual reproduction is no longer associated with water. Pollination in gymnosperms is carried out by the wind, and the seeds are equipped with adaptations for dispersal by animals. All this contributed to the resettlement of seed plants.

Question 4. Describe the fauna of the Paleozoic.

The animal world in the Paleozoic era developed extremely rapidly and was represented by a large number of diverse forms. Life flourished in the seas. At the very beginning of this era (570 million years ago), all the main types of animals already existed, except for chordates. Sponges, corals, echinoderms, molluscs, huge predatory crustaceans - this is an incomplete list of the inhabitants of the seas of that time.

Question 5. What are the main aromorphoses in the evolution of vertebrates in the Paleozoic.

In vertebrates of the Paleozoic era, a number of aromorphoses can be traced. Of these, the appearance of jaws in armored fish, the pulmonary method of breathing, and the structure of fins in lobe-finned fish are noted. Later, major aromorphoses in the development of vertebrates were the appearance of internal fertilization and the formation of a number of egg shells that protect the embryo from drying out, a complication in the structure of the heart and lungs, and keratinization of the skin. These profound changes led to the emergence of a class of reptiles.

Question 6. What environmental conditions and structural features of vertebrates served as prerequisites for their exit to land?

Most of the land was a lifeless desert. Along the banks of freshwater reservoirs, annelids and arthropods lived in dense thickets of plants. The climate is dry, with sharp fluctuations in temperature during the day and seasonally. The water level in rivers and reservoirs often changed. Many reservoirs completely dried up and froze in winter. When water bodies dried up, aquatic vegetation died, and plant residues accumulated. Their decomposition consumed oxygen dissolved in water. All this created a very unfavorable environment for fish. Under these conditions, only breathing atmospheric air could save them.

Question 7. Why did amphibians of the Carboniferous period achieve biological prosperity?

Reptiles (reptiles) acquired some properties that allowed them to finally break the connection with the aquatic habitat. Internal fertilization and the accumulation of yolk in the egg made it possible for the reproduction and development of the embryo on land. The keratinization of the skin and the more complex structure of the kidney contributed to a sharp decrease in water loss by the body and, as a result, to a wide distribution. The appearance of the chest provided a more efficient type of breathing than in amphibians - suction. The lack of competition caused the widespread distribution of reptiles on land and the return of some of them - ichthyosaurs - to the aquatic environment.

Question 8. Summarize the information obtained from this paragraph into a single table "Evolution of the flora and fauna in the Paleozoic era."

Question 9. Give examples of the relationship between the evolutionary transformations of plants and animals in the Paleozoic.

In the Paleozoic, the organs of reproduction and cross-fertilization in angiosperms improved in parallel with the evolution of insects;

Question 10. Can it be argued that aromorphoses are based on idioadaptation - private adaptations to specific environmental conditions? Give examples.

Aromorphoses are indeed based on particular adaptations to specific environmental conditions. an example of this is the emergence of gymnosperms due to climate change - it has become warmer and more humid. In animals, such an example is the appearance of paired limbs as a result of the deterioration of habitat conditions and subsequent access to land.

the germinal stage of a seed plant, which is formed in the process of sexual reproduction and serves for settling. Inside the seed is an embryo, consisting of an embryonic root, a stalk and one or two leaves, or cotyledons. Flowering plants are divided into dicots and monocots according to the number of cotyledons. In some species, such as orchids, individual parts of the embryo are not differentiated and begin to form from certain cells immediately after germination.

A typical seed contains a supply of nutrients for the embryo, which will have to grow for some time without the light needed for photosynthesis. This reserve can occupy most of the seed, and sometimes is located inside the embryo itself - in its cotyledons (for example, in peas or beans); then they are large, fleshy and determine the general shape of the seed. When the seed germinates, they can be taken out of the ground on an elongating stalk and become the first photosynthetic leaves of a young plant. In monocots (for example, wheat and corn), the food supply is the so-called. endosperm is always separated from the embryo. The ground endosperm of grain crops is a well-known flour.

In angiosperms, the seed develops from the ovule - a tiny thickening on the inner wall of the ovary, i.e. the bottom of the pistil located in the center of the flower. The ovary may contain from one to several thousand ovules.

Each of them contains an egg. If, as a result of pollination, it is fertilized by sperm that penetrates the ovary from the pollen grain, the ovule develops into a seed. It grows, and its shell becomes dense and turns into a two-layer seed coat. Its inner layer is colorless, slimy and is able to swell strongly, absorbing water. This will come in handy later, when the growing embryo will have to break through the seed coat. The outer layer can be oily, soft, filmy, hard, papery, and even woody. On the seed peel, the so-called. hilum - the area by which the seed was connected to the peduncle, which attached it to the parent organism.

The seed is the basis for the existence of modern flora and fauna. Without a seed, there would be no coniferous taiga, deciduous forests, flowering meadows, steppes, grain fields on the planet, there would be no birds and ants, bees and butterflies, humans and other mammals. All this appeared only after the plants in the course of evolution had seeds, inside which life can, without declaring itself in any way, be preserved for weeks, months and even for many years. The miniature plant germ in the seed is capable of traveling long distances; he is not tied to the earth by roots, like his parents; does not need water or oxygen; he waits in the wings to get to a suitable place and wait for favorable conditions, to begin development, which is called the germination of the seed.

The evolution of seeds.

For hundreds of millions of years, life on Earth did without seeds, as it does without them now on two-thirds of the planet's surface covered with water. Life originated in the sea, and the first plants that conquered land were still seedless, but only the appearance of seeds allowed photosynthetic organisms to fully master this new habitat for them.

The first land plants.

Among large organisms, the first attempt to gain a foothold on land was most likely made by marine macrophytes - algae that found themselves on stones heated by the sun at low tide. They reproduced by spores - single-celled structures dispersed by the parent organism and capable of developing into a new plant. Algae spores are surrounded by thin shells, so they do not tolerate drying. Under water, such protection is quite enough. Spores there are spread by currents, and since the temperature of the water fluctuates relatively little, they do not need to wait long for favorable conditions for germination.

The first land plants also reproduced by spores, but the obligatory change of generations was already fixed in their life cycle. The sexual process included in it ensured the combination of the hereditary characteristics of the parents, as a result of which the offspring combined the advantages of each of them, becoming larger, more enduring, and more perfect in structure. At a certain stage, such a progressive evolution led to the appearance of liverworts, mosses, club mosses, ferns and horsetails, which had already completely left the reservoirs on land. However, spore reproduction did not yet allow them to spread beyond marshy places with moist and warm air.

Spore plants of the Carboniferous period.

At this stage of the development of the Earth (about 250 million years ago), giant forms with partially lignified trunks appeared among the ferns and lycopsids. Horsetails were not inferior in size to them, the hollow stems of which were covered with green bark soaked in silica. Wherever plants appeared, they were followed by animals, mastering new types of habitats. In the humid twilight of the coal jungle, there were many large insects (up to 30 cm in length), giant centipedes, spiders and scorpions, amphibians that looked like huge crocodiles, and salamanders. There were dragonflies with a wingspan of 74 cm and cockroaches 10 cm long.

Tree ferns, club mosses and horsetails possessed all the qualities necessary for living on land, except for one thing - they did not form seeds. Their roots effectively absorbed water and mineral salts, the vascular system of the trunks reliably carried the substances necessary for life to all organs, and the leaves actively synthesized organic substances. Even the spores have improved and acquired a strong cellulose shell. Not afraid of drying out, they are carried by the wind over considerable distances and could not germinate immediately, but after a certain period of dormancy (the so-called dormant spores). However, even the most perfect spore is a unicellular formation; unlike seeds, it dries quickly and does not contain a supply of nutrients, and therefore is not able to wait long for favorable conditions for development. Yet the formation of resting spores was an important milestone on the way to seed plants.

For many millions of years, the climate on our planet remained warm and humid, but evolution in the fertile wilds of the coal bogs did not stop. Tree-like spore-bearing plants first developed primitive forms of true seeds. Seed ferns appeared, lycopsids (famous representatives of the genus Lepidodendron- in Greek, this name means "scaly tree") and cordaites with solid woody trunks.

Although there are few fossils of these organisms that lived hundreds of millions of years ago, tree-like seed ferns are known to have existed even before the Carboniferous. In the spring of 1869, the Skohary Creek in the Catskills, New York, flooded heavily. The flood swept away bridges, knocked down trees, and heavily washed away the shore near the village of Gilboa. This incident would have long been forgotten if the falling water had not revealed to the observers an impressive collection of strange stumps. Their bases greatly expanded, like those of swamp trees, the diameter reached 1.2 m, and their age was 300 million years. Details of the structure of the bark were well preserved, fragments of branches and leaves were scattered nearby. Naturally, all this, including the silt from which the stumps rose, was petrified. Geologists have dated the fossils to the Upper Devonian, pre-Carboniferous, and determined that they correspond to tree ferns. For the next fifty years, only paleobotanists remembered the find, and then the village of Gilboa presented another surprise. Together with the fossilized trunks of ancient ferns, this time their branches with real seeds were discovered. Now these extinct trees belong to the genus Eospermatopteris, which translates as "dawn seed fern." (“dawn”, because we are talking about the earliest seed plants on Earth).

The legendary Carboniferous period ended when geological processes complicated the planet's relief, crushing its surface into folds and dismembering it with mountain ranges. Lowland swamps were buried under a thick layer of sedimentary rocks washed off the slopes. The continents changed their shape, pushing the sea and deviating ocean currents from their previous course, ice caps began to grow in places, and red sand covered vast expanses of land. Giant ferns, club mosses and horsetails died out: their spores were not adapted to the harsher climate, and the attempt to switch to propagation by seeds turned out to be too weak and uncertain.

The first true seed plants.

The coal forests perished and were covered with new layers of sand and clay, but some trees survived by forming winged seeds with a strong shell. Such seeds could spread faster, longer, and therefore over longer distances. All this increased their chances of finding favorable conditions for germination or waiting for them to come.

Seeds were destined to revolutionize life on Earth at the beginning of the Mesozoic era. By this time, two types of trees, cycads and ginkgos, had escaped the sad fate of other carboniferous vegetation. These groups began to co-populate the Mesozoic continents. Encountering no competition, they spread from Greenland to Antarctica, making the vegetation cover of our planet almost homogeneous. Their winged seeds traveled through mountain valleys, flew over lifeless rocks, sprouted in sandy patches between rocks and among alluvial gravel. Probably, small mosses and ferns, which survived the climate change on the planet at the bottom of ravines, in the shade of cliffs and along the shores of lakes, helped them explore new places. They fertilized the soil with their organic remains, preparing its fertile layer for the settlement of larger species.

Mountain ranges and vast plains remained bare. Two types of "pioneer" trees with winged seeds, having spread around the planet, were tied to wet places, since their eggs were fertilized by flagellated, actively swimming spermatozoa, like those of mosses and ferns.

Many spore plants form spores of different sizes - large megaspores, which give rise to female gametes, and small microspores, during the division of which motile spermatozoa arise. To fertilize an egg, they need to swim up to it through the water - while a drop of rain and dew is quite enough.

In cycads and ginkgo, megaspores are not dispersed by the parent plant, but remain on it, turning into seeds, however, spermatozoa are motile, so dampness is needed for fertilization. The external structure of these plants, especially their leaves, also brings them closer to the fern-like ancestors. The preservation of the ancient method of fertilization by spermatozoa floating in water led to the fact that, despite the relatively hardy seeds, prolonged drought remained an insurmountable problem for these plants, and the conquest of land was suspended.

The future of terrestrial vegetation was provided by trees of a different type, growing among cycads and ginkgoes, but having lost flagellated spermatozoa. These were the araucaria (genus Araucaria), coniferous descendants of Carboniferous cordaites. In the era of cycads, araucaria began to form huge amounts of microscopic pollen grains, corresponding to microspores, but dry and dense. They were carried by the wind to megaspores, more precisely, to the ovules formed from them with eggs, and germinated with pollen tubes that delivered immobile sperm to the female gametes.

Thus, pollen appeared in the world. The need for water for fertilization disappeared, and plants rose to a new evolutionary stage. The formation of pollen led to an enormous increase in the number of seeds developing on each individual tree, and consequently to the rapid spread of these plants. The ancient araucaria also had a method of settlement, preserved in modern conifers, with the help of hard winged seeds, easily carried by the wind. So, the first conifers appeared, and over time, well-known species of the pine family.

Pine produces two types of cones. Men's length approx. 2.5 cm and 6 mm in diameter are grouped at the ends of the uppermost branches, often in bunches of ten or more, so that a large tree can have several thousand of them. They scatter pollen, showering everything around with a yellow powder. The female cones are larger and grow on the tree below the male ones. Each of their scales resembles a scoop in shape - wide on the outside and tapering towards the base, with which it is attached to the woody axis of the cone. On the upper side of the scale, closer to this axis, two megaspores are openly located, waiting for pollination and fertilization. Pollen grains carried by the wind fly inside the female cones, roll down the scales to the ovules and come into contact with them, which is necessary for fertilization.

Cycads and ginkgoes could not compete with more advanced conifers, which, effectively dispersing pollen and winged seeds, not only pushed them out, but also mastered new, previously inaccessible corners of the land. Taxodiaceae became the first coniferous dominants (now they include, in particular, sequoias and swamp cypresses). Having spread all over the world, these beautiful trees covered all parts of the world with uniform vegetation for the last time: their remains are found in Europe, North America, Siberia, China, Greenland, Alaska and Japan.

Flowering plants and their seeds.

Conifers, cycads and ginkgos belong to the so-called. gymnosperms. This means that their ovules are located openly on the seed scales. Flowering plants constitute the department of angiosperms: their ovules and the seeds developing from them are hidden from the external environment in an expanded base of the pistil, called the ovary.

As a result, the pollen grain cannot reach the ovule directly. For the fusion of gametes and the development of the seed, a completely new plant structure is needed - a flower. Its male part is represented by stamens, the female part by pistils. They can be in the same flower or in different flowers, even on different plants, which in the latter case are called dioecious. Dioecious species include, for example, ash trees, hollies, poplars, willows, date palms.

For fertilization to occur, the pollen grain must land on the top of the pistil—the sticky, sometimes pinnate stigma—and adhere to it. The stigma releases chemicals, under the influence of which the pollen grain germinates: the living protoplasm, emerging from under its hard shell, forms a long pollen tube that penetrates the stigma, spreads further deep into the pistil along its elongated part (column) and ultimately reaches the ovary with ovules. Under the influence of chemical attractants, the nucleus of the male gamete moves along the pollen tube to the ovule, penetrates into it through a tiny hole (micropyle) and merges with the nucleus of the egg. This is how fertilization occurs.

After that, the seed begins to develop - in a humid environment, richly supplied with nutrients, protected by the walls of the ovary from external influences. Parallel evolutionary transformations are also known in the animal world: external fertilization, typical, say, for fish, is replaced by internal fertilization on land, and the embryo of mammals is formed not in eggs laid in the external environment, as, for example, in typical reptiles, but inside the uterus. The isolation of the developing seed from extraneous influences allowed the flowering plants to boldly “experiment” with its shape and structure, and this, in turn, led to an avalanche-like appearance of new forms of terrestrial plants, the diversity of which began to increase at a pace unprecedented in previous eras.

The contrast with gymnosperms is obvious. Their “naked” seeds lying on the surface of the scales, regardless of the type of plant, are approximately the same: teardrop-shaped, covered with a hard skin, to which a flat wing is sometimes attached, formed by the cells surrounding the seed. It is not surprising that for many millions of years the form of gymnosperms remained very conservative: pines, spruces, firs, cedars, yews, cypresses are very similar to each other. True, in junipers, yew and ginkgo seeds can be confused with berries, but this does not change the overall picture - the extreme uniformity of the general plan of the structure of gymnosperms, the size, type and color of their seeds in comparison with the huge wealth of flowering forms.

Despite the scarcity of information about the first stages of the evolution of angiosperms, it is believed that they appeared by the end of the Mesozoic era, which ended about 65 million years ago, and at the beginning of the Cenozoic era they already conquered the world. The oldest known to science flowering genus - Claytonia. Its fossils have been found in Greenland and Sardinia, i.e., it is likely that even 155 million years ago it was as widespread as the cycads. Leaves at Claytonia palmately complex, as in the current horse chestnuts and lupins, and the fruits are berry-like with a diameter of 0.5 cm at the end of a thin peduncle. Perhaps these plants were brown or green in color. The bright colors of angiosperm flowers and fruits came later, paralleling the evolution of the insects and other animals they were meant to attract. berry Claytonia four-seeded; on it you can discern something resembling the remnant of a stigma.

In addition to the extremely rare fossil remains, unusual modern plants, grouped in the order Gnetales, provide some insight into the first flowering plants. One of their representatives is a conifer (genus Ephedra), found particularly in the deserts of the southwestern United States; outwardly, it looks like several leafless rods extending from a thick stem. Another genus is velvichia ( Welwitschia) grows in the desert off the southwestern coast of Africa, and the third is gnetum ( Gnetum) is a low shrub of the Indian and Malay tropics. These three genera can be considered "living fossils", demonstrating possible pathways for the transformation of gymnosperms into angiosperms. The cones of the conifer outwardly resemble flowers: their scales are divided into two parts, resembling petals. Velvichia has only two wide ribbon-like leaves up to 3 m long, completely different from conifer needles. Gnetum seeds are provided with an additional shell, making them look like angiosperm drupes. It is known that angiosperms differ from gymnosperms in the structure of wood. Among the oppressors, it combines the features of both groups.

Seed dispersal.

The viability and diversity of the plant world depend on the ability of species to spread. The parent plant is rooted in one place all its life, therefore, its offspring must find another. This task of developing new space was entrusted to the seeds.

First, the pollen must land on the pistil of a flower of the same species, i.e. pollination must take place. Second, the pollen tube must reach the ovule, where the nuclei of the male and female gametes will fuse. Finally, the mature seed has to leave the parent plant. The probability that a seed will germinate and take root successfully in a new place is a tiny fraction of a percent, so plants are forced to rely on the law of large numbers and disperse as many seeds as possible. The last parameter is generally inversely proportional to their chances of survival. Let's compare, for example, a coconut palm and orchids. The coconut palm has the largest seeds in the plant world. They are able to swim indefinitely in the oceans until the waves throw them onto the soft coastal sand, where the competition of seedlings with other plants will be much weaker than in the forest more often. As a result, the chances of settling down for each of them are quite high, and one mature palm tree, without risk to the species, usually produces only a few dozen seeds per year. Orchids, on the other hand, have the smallest seeds in the world; in tropical forests, they are carried by weak air currents among high crowns and germinate in moist cracks in the bark on tree branches. The situation is complicated by the fact that on these branches they need to find a special type of fungus, without which germination is impossible: small orchid seeds do not contain nutrient reserves and in the first stages of seedling development they receive them from the fungus. It is not surprising that in one fruit of a miniature orchid there are several thousand of these seeds.

Angiosperms are not limited to producing a variety of seeds as a result of fertilization: the ovaries, and sometimes other parts of the flowers, develop into unique seed-containing structures - fruits. The ovary can become a green bean that protects the seeds until they ripen, turn into a tough coconut that can make long sea voyages, into a juicy apple that an animal will eat in a secluded place, using the pulp, but not the seeds. Berries and drupes are a favorite delicacy of birds: the seeds of these fruits are not digested in their intestines and fall into the soil along with excrement, sometimes many kilometers from the parent plant. The fruits are winged and fluffy, and the form of appendages that increase volatility is much more diverse than that of pine seeds. The wing of the ash fruit resembles an oar, in the elm it looks like a brim of a hat, in the maple the paired fruits - diptera - resemble soaring birds, in the ailanthus the wings of the fruit are twisted at an angle to each other, forming, as it were, a propeller.

These adaptations allow flowering plants to use external factors very effectively for seed dispersal. However, some species do not count on outside help. So, the fruits of touchy are a kind of catapult. Geraniums use a similar mechanism. A rod passes inside their long fruit, to which four for the time being straight and joined together valves are attached - they hold firmly from above, weakly from below. When ripe, the lower ends of the valves come off the base, twist sharply towards the top of the rod and scatter the seeds. In the ceanothus shrub well-known in America, the ovary turns into a berry, similar in structure to a time bomb. The pressure of the juice inside is so high that after maturation, a warm enough sunbeam to make its seeds scatter like living shrapnel in all directions. Boxes of ordinary violets, having dried up, burst and scatter seeds around them. Hamamelis fruits act like a howitzer: in order for the seeds to fall farther, they shoot them at a high angle to the horizon. In the knotweed virgin, in the place where the seeds are attached to the plant, a spring-like structure is formed that discards mature seeds. In oxalis, the shells of the fruit first swell, and then crack and shrink so sharply that the seeds fly out through the cracks. Arceutobium is tiny, due to the hydraulic pressure inside the berries, it pushes the seeds out of them like miniature torpedoes.

Viability of seeds.

The embryos of many seeds are provided with nutrients and do not suffer from drying out under an airtight shell, and therefore they can wait for favorable conditions for many months and even years: in sweet clover and alfalfa - 20 years, in other legumes - more than 75, in wheat, barley and oats - to ten. Weed seeds are distinguished by good viability: in curly sorrel, mullein, black mustard and pepper knotweed, they germinate after lying in the ground for half a century. It is believed that 1.5 tons of weed seeds are buried per 1 hectare of ordinary agricultural soil, which are just waiting for an opportunity to get closer to the surface and sprout. Cassia and lotus seeds remain viable for centuries. The record for viability is still held by the seeds of the walnut lotus, discovered several years ago in the bottom silt of one of the dried-up lakes in Manchuria. It was established by radiocarbon method that their age is 1040 ± 120 years.

First land plants and animals

WHERE LIFE ORIGINATED Life originated in water. Here the first plants appeared - algae. However, at some point, land appeared, which had to be populated. Pioneers among animals were lobe-finned fish. And among plants?

WHAT THE FIRST PLANTS LOOKED LIKE Once upon a time, our planet was inhabited by plants that had only a stem. They were attached to the ground with special outgrowths - rhizoids. These were the first plants to reach land. Scientists call them psilophytes. This is a Latin word. Translated, it means "naked plants". The psilophytes really looked "naked". They had only branching stems with outgrowths of balls in which spores were stored. They are very similar to the "alien plants" that are depicted in illustrations for fantastic stories. Psilophytes became the first land plants, but they lived only in swampy areas, since they did not have a root, and they could not extract water and nutrients in the soil. Scientists believe that once these plants created huge carpets over the bare surface of the planet. There were both tiny plants and very large ones, taller than human growth.

THE FIRST ANIMALS ON EARTH The oldest traces of animal life on Earth date back a billion years, but the oldest fossils of the animals themselves are approximately 600 million years old and date back to the Vendian period. The first animals that appeared on Earth as a result of evolution were microscopically small and soft-bodied. They lived on the seabed or in bottom silt. Such creatures could hardly be petrified, and the only clue to unraveling the mystery of their existence is indirect traces, such as the remains of burrows or passages. But despite their tiny size, these most ancient animals were resilient and gave rise to the first known animals on Earth - the Ediacaran fauna.

The evolution of life on Earth began with the appearance of the first living being - about 3.7 billion years ago - and continues to this day. The similarity between all organisms indicates the presence of a common ancestor from which all other living beings descended.

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psilophyta (Psilophyta), the most ancient and primitive extinct group (department) of higher plants. They were characterized by the apical arrangement of sporangia (See Sporangium) and equispores, the absence of roots and leaves, dichotomous or dichopodial (pseudomonopodial) branching, and a primitive anatomical structure. The conducting system is a typical Protostele. The protoxylem was located in the center of the xylem; the metaxylem consisted of tracheids with annular or (rarely) scalariform thickenings. Support tissues were absent. R. did not yet possess the ability for secondary growth (they had only apical meristems). Sporangia are primitive, from spherical (about 1 mm in diameter) to oblong-cylindrical (up to 12 mm long), thick-walled. R.'s gametophytes are not reliably known (some authors consider horizontal rhizome-like organs, the so-called rhizomoids, to be gametophytes).

R. grew in wet and swampy places, as well as in shallow coastal waters. R.'s department includes one class - rhyniopsida (Rhyniopsida) with two orders - Rhyniales (families Cooksoniaceae, Rhyniaceae, Hedeiaceae) and Psilophytales (family Psilophytaceae). The order Rhyniales is characterized by dichotomous branching and a thin, poorly developed stele. Xylem of tracheids with ringed thickenings. The oldest representative of R. is the genus Cooksonia, originally discovered in Wales in the deposits of the end of the Silurian period (about 400 million years ago). The most fully studied are the Lower Devonian genera - rhynia and partly a horneophyte, in which the rhizomoid (stems departed from it upwards, numerous Rhizoids downwards) was divided into clearly arranged tuberous segments, devoid of conductive tissues and consisted entirely of parenchymal cells. It is believed that in the course of evolution R.'s rhizomoids gave rise to roots. In both genera, the sporangium wall was multi-layered, covered with a cuticle (See Cuticle). The horneophyte is characterized by a peculiar spore-bearing cavity, which forms a dome that arch-like covers the central column of sterile tissue, which is a continuation of the stem phloem. This horneophyte resembles modern Sphagnum. Rhynia families also include the genus teniokrada, many species of which formed underwater thickets in the Middle and Upper Devonian. The Lower Devonian genera Khedea and Yaravia are sometimes distinguished into a separate family of Hedei. The Lower Devonian genus Sciadophyte, usually classified as a separate family of Sciadophytes, is a small plant consisting of a rosette of simple or weakly dichotomized thin stems with a stele. The order Psilophytales is characterized by dichopodial branching and a more strongly developed stele. In the most famous genus, psilophyte (from Lower Devonian deposits in Eastern Canada), unequally developed branches formed a false main axis of dichopodium with thinner side branches: the stem was surrounded by a cutinized epidermis with stomata; the surface of the stem was bare or covered with spines 2–2.5 mm long, the ends of which widened disc-like, which probably indicated their secretory role. The sporangia opened with a longitudinal fissure. The Lower Devonian genera Trimerophyte and Pertika are close to psilophyte.

The study of the structure of R. and their evolutionary relationships is of great importance for the evolutionary morphology and phylogeny of higher plants. Apparently, the original organ of the Sporophyte of higher plants was a dichotomously branching stem with apical sporangia; roots and leaves are later than sporangium and stem. There is every reason to consider R. the original ancestral group from which bryophytes, lycopsids, horsetails, and ferns originated. According to another point of view, bryophytes and lycopsids have only a common origin with P.

Lit .: Fundamentals of paleontology. Algae, bryophytes, psilophytes, lycopsids, arthropods, ferns, M., 1963; Traite de paleobotanique, t. 2, Bryophyta. psilophyta. Lycophyta, P., 1967.

A. L. Takhtadzhyan.

Planet Earth was formed over 4.5 billion years ago. The first single-celled life forms appeared, possibly about 3 billion years ago. First it was bacteria. They are classified as prokaryotes because they do not have a cell nucleus. Eukaryotic (with nuclei in the cells) organisms appeared later.

Plants are eukaryotes capable of photosynthesis. In the process of evolution, photosynthesis appeared earlier than eukaryotes. At that time it existed in some bacteria. These were blue-green bacteria (cyanobacteria). Some of them have survived to this day.

According to the most common hypothesis of evolution, the plant cell was formed by entering a heterotrophic eukaryotic cell of a photosynthetic bacterium that was not digested. Further, the process of evolution led to the emergence of a single-celled eukaryotic photosynthetic organism with chloroplasts (their predecessors). This is how unicellular algae appeared.

The next stage in the evolution of plants was the emergence of multicellular algae. They reached a great diversity and lived exclusively in the water.

The surface of the earth did not remain unchanged. Where the earth's crust was rising, land gradually arose. Living organisms had to adapt to new conditions. Some ancient algae were gradually able to adapt to the terrestrial way of life. In the process of evolution, their structure became more complicated, tissues appeared, primarily integumentary and conductive.

The psilophytes, which appeared about 400 million years ago, are considered the first land plants. They have not survived to this day.

Further evolution of plants, associated with the complication of their structure, was already on land.

During the time of the psilophytes, the climate was warm and humid. Psilophytes grew near water bodies. They had rhizoids (like roots), with which they were fixed in the soil and absorbed water. However, they did not have true vegetative organs (roots, stems, and leaves). The movement of water and organic substances through the plant was ensured by the emerging conductive tissue.

Later, ferns and mosses originated from psilophytes. These plants have a more complex structure, they have stems and leaves, they are better adapted to living on land. However, just like the psilophytes, they remained dependent on water. During sexual reproduction, in order for the sperm to reach the egg, they need water. Therefore, they could not "go" far from wet habitats.

In the Carboniferous period (about 300 million years ago), when the climate was humid, ferns reached their dawn, many of their woody forms grew on the planet. Later, dying off, it was they who formed deposits of coal.

When the climate on Earth began to become colder and drier, ferns began to die out en masse. But some of their species before that gave rise to the so-called seed ferns, which, in fact, were already gymnosperms. In the subsequent evolution of plants, seed ferns died out, giving rise to other gymnosperms before this. Later, more advanced gymnosperms appeared - conifers.

The first plants on earth

Pollination took place with the help of wind. Instead of spermatozoa (mobile forms), they formed sperm (immobile forms), which were delivered to the egg by special formations of pollen grains. In addition, gymnosperms did not form spores, but seeds containing a supply of nutrients.

The further evolution of plants was marked by the appearance of angiosperms (flowering). This happened about 130 million years ago. And about 60 million years ago they began to dominate the Earth. Compared to gymnosperms, flowering plants are better adapted to life on land. It can be said that they began to use the possibilities of the environment more. So their pollination began to occur not only with the help of wind, but also through insects. This increased the efficiency of pollination. Seeds of angiosperms are found in fruits, which provide more efficient distribution. In addition, flowering plants have a more complex tissue structure, for example, in the conducting system.

Currently, angiosperms are the most numerous group of plants in terms of the number of species.

Main article: Ferns

Rhyniophytes is an extinct group of plants. Some scientists consider them to be the ancestors of mosses, ferns, horsetails and club mosses. Others suggest that rhinophytes mastered the land at the same time as mosses.

The first land plants - rhinophytes appeared about 400 million years ago. Their body consisted of green twigs. Each branch branched, dividing into two parts. The vein cells contained chlorophyll and photosynthesis took place. Material from the site http://wikiwhat.ru

Rhinophytes grew in moist places. They were attached to the soil by rhizoids - outgrowths on the surface of horizontally located veto-checks.

The first land plants

At the ends of the branches were spore-bearing parts, in which spores ripened. In rhinophytes, conductive and mechanical tissues have already begun to form. In the process of evolution, due to the occurrence of hereditary changes and natural selection, an integumentary tissue with stomata regulating the evaporation of water was formed on the surface of rhinophyte branches.

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On this page, material on the topics:

• Conductive integumentary and mechanical tissues in rhinophyte and ferns

• Life cycle of rionophytes diagram

• The story of rhinophyta answer

• Message first land plant

• When and from what group of algae did the first reniophytes appear?

Origin and systematics of higher plants.

Higher plants probably evolved from some kind of algae. This is evidenced by the fact that in the geological history of the plant world, higher plants were preceded by algae. The following facts testify in favor of this assumption: the similarity of the most ancient extinct group of higher plants - rhinophytes - with algae, a very similar nature of their branching; similarity in the alternation of generations of higher plants and many algae; the presence of flagella and the ability to swim independently in the male germ cells of many higher plants; similarity in structure and function of chloroplasts.

It is believed that higher plants evolved from green algae, freshwater or brackish water. They had multicellular gametangia, isomorphic alternation of generations in the development cycle.

The first land plants found in the fossil state were rhinophytes(rhinia, hornea, horneophyton, sporogonites, psilophyte, etc.).

After reaching land, higher plants developed in two main directions and formed two large evolutionary branches - haploid and diploid.

The haploid branch of the evolution of higher plants is represented by the bryophyte division (Bryophyta). In the development cycle of mosses, the gametophyte, the sexual generation (the plant itself), predominates, while the sporophyte, the asexual generation, is reduced and is represented by a sporogon in the form of a box on a leg.

The second evolutionary branch of higher plants is represented by all other higher plants.

The sporophyte under terrestrial conditions turned out to be more viable and adapted to various environmental conditions. This group of plants conquered land more successfully.

Currently, higher plants number over 300,000 species. They dominate the Earth, inhabit it from the Arctic territories to the equator, from the humid tropics to dry deserts. They form various types of vegetation - forests, meadows, swamps, fill reservoirs. Many of them reach gigantic proportions.

Taxonomy of higher plants- This is a branch of botany that develops a natural classification of higher plants based on the study and selection of taxonomic units, establishes family ties between them in their historical development. The most important concepts of taxonomy are taxonomic (systematic) categories and taxa.

plant evolution

According to the rules of botanical nomenclature, the main taxonomic categories are: species (species), genus (genus), family (familia), order (ordo), class (classis), department (devisio), kingdom (regnum). If necessary, intermediate categories can also be used, for example, subspecies (subspecies), genus (subgenus), subfamily (subfamilia), superorder (superordo), superregnum (superregnum).

For species starting from 1753 - the date of publication of the book K. Linnaeus"Plant species" - accepted binominal names, consisting of two Latin words. The first designates the genus to which this species belongs, the second - the specific epithet: for example, sticky alder - Alnus glutinosa.

For plant families, the ending is aceae, for orders - ales, for subclasses - idae, for classes - psida, for divisions - phyta. The standard uninominal name is based on the name of any genus included in this family, order, class, etc.

Modern science of the organic world divides living organisms into two kingdoms: pre-nuclear organisms (Procariota) and nuclear organisms (Eucariota). The super-kingdom of pre-nuclear organisms is represented by one kingdom - shotguns (Mychota) with two sub-kingdoms: bacteria (Bacteriobionta) and cyanothea, or blue-green algae (Cyanobionta).

The superkingdom of nuclear organisms includes three kingdoms: animals (Animalia), fungi (Mycetalia, Fungi, or Mycota) and plants (Vegetabilia, or Plantae).

The animal kingdom is divided into two sub-kingdoms: protozoa and multicellular animals (Metazoa).

The kingdom of fungi is divided into two sub-kingdoms: lower fungi (Myxobionta) and higher fungi (Mycobionta).

The plant kingdom includes three sub-kingdoms: scarlet(Rhodobionta), real algae(Phycobionta) and higher plants(Embryobionta).

Our planet has not always been green. A long time ago, when life was just emerging, the land was empty and lifeless - the first forms chose the oceans as their habitat. But gradually the earth's surface also began to be mastered by various creatures. The first plants on Earth are also the earliest inhabitants of land. What were the ancestors of modern representatives of the flora?

So, imagine the Earth 420 million years ago, in an era called the Silurian period. This date was not chosen by chance - it was at this time, scientists believe, that plants finally began to conquer the land.

For the first time, the remains of cooksonia were discovered in Scotland (the first representative of the terrestrial flora was named after Isabella Cookson, a famous paleobotanist). But scientists suggest that it was distributed throughout the globe.

It was not so easy to get out of the waters of the oceans and start developing the land. To do this, the plants had to literally rebuild the entire body: to acquire a shell resembling a cuticle that prevents drying out, and to acquire special stomata, with which it was possible to regulate evaporation and absorb the substances necessary for life.

Cooksonia, which is a thin green stems, not exceeding five centimeters in height, was considered one of the most developed plants. But the atmosphere of the Earth and its inhabitants were rapidly changing, and the most ancient representative of the flora was losing ground more and more. At the moment, the plant is considered extinct.

The remains of the nematothallus do not even remotely resemble plants - they look more like shapeless black spots. But despite the strange appearance, in terms of development, this plant has gone far ahead of its comrades in its habitat. The fact is that the cuticle of the nematothallus is already more similar to the parts of existing plants - it consisted of formations resembling modern cells, which is why it was called pseudocellular. It should be noted that in other species this shell looked just like a continuous film.

Nematothallus has given a lot of food for thought to the scientific world. Some scientists attributed it to red algae, others were inclined to believe that they had a lichen in front of them. And until now, the mystery of this ancient organism has not been solved.

Rinia and almost all other ancient plants with a vascular structure are classified as rhinophytes. Representatives of this group have not grown on Earth for a long time. However, this fact does not at all prevent scientists from studying these living creatures that once dominated the land - a lot of fossils found in many parts of the world make it possible to judge both the appearance and the structure of such plants.

Rhiniophytes have several important features that allow us to assert that these living creatures are completely different from their descendants. First, their stem was not covered with soft bark: scaly processes grew on it. Secondly, rhinophytes reproduced exclusively with the help of spores, which were formed in special organs called sporangia.

But the most important difference is that these plants did not have a root system as such. Instead, there were root formations covered with "hairs" - rhizoids, with the help of which rhinia absorbed water and substances necessary for life.

This plant was recently considered a representative of the animal world. The fact is that its remains - small, rounded in shape - were originally mistaken for frog or fish eggs, algae, or even eggs of long-extinct shell scorpions. The spores of the parka, found in 1891, put an end to the misconceptions.

The plant lived on our planet about 400 million years ago. This time refers to the beginning of the Devonian period.

Pachiteki remains, as well as the parka fossils found, are small balls (the largest of those discovered has a diameter of 7 millimeters). Quite little is known about this plant: scientists managed to establish only the fact that it consisted of tubules located radially and converging in the center where the nucleus was located.

This plant is a dead end branch of the development of flora, in fact, like parks and rhinia. It was not possible to establish for certain what was the impetus for their emergence, and why they died out. The only reason, according to scientists, is the development of vascular plants, which simply replaced their less developed relatives.

The plants that got out on land chose a completely different path of development. It was thanks to them that the animal world was born and, accordingly, a reasonable form of life appeared - man. And who knows what our planet would look like now if the rhinii, parkas and cooksonia had not decided to explore the land? ..

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