Angiosperms are the apex of the evolution of the plant world

The emergence of plants on land, which occurred in the beginningSilurian period (approximately 435 million years ago), was accompanied by a number of qualitative evolutionary changes. Plants were forced to adapt to the changing conditions of terrestrial life. In the process of evolution, they have new tissues (epidermis, xylem, phloem, mechanical tissue) and organs (leaf sprout shoot and root). Over time, primitive rhyniophytes, not having formed shoots, were replaced by fern-like species that spread throughout the Earth in the Devonian (about 400 million years ago). In the Mesozoic (235-132 million years ago), gymnosperms dominate the planet, and after them angiosperms appear that are considered the apex of the evolution of the plant world.

Angiosperms reach their heyday inCenozoic - geological epoch, which began about 66 million years ago and continues to the present. Although, judging by the imprints in the strata of rocks, they appeared in the Mesozoic (about 130 million years ago), but these were a few and primitive forms. The most ancient angiosperms are representatives of the nymphaeid group, which include water lilies.

At present this department is the mostnumerous. Between the equator and both poles there is no such site on which conditions exist for plant life, but no angiosperms are found. In addition to the widest geographical diversity, angiosperms are characterized by the multifaceted forms and methods of growth. Miniature duckweed, tightening the surface of the reservoir, and a huge baobab that lives for hundreds and even thousands of years, thorny cacti and elegant orchids, a modest daisy and giant rafflesia, with flowers of meter diameter - they all belong to this department. Quite a large group - aquatic angiosperms, inhabiting freshwater (mainly) and saline (less often) water bodies. Such species are not primitive, on the contrary, it is the result of the adaptation of terrestrial forms to the aquatic environment.

The main feature of angiosperms is the presenceflower, generative organ responsible for sexual reproduction and attracting agents of pollination. Hence the second name of the department - Flowering plants (Magnoliophita).

Reproduction of angiospermous plantsis directly related to the process of pollination, which involves insects, birds, mammals, wind and water. In most climatic zones of the planet, the main agents of pollination are insects. In tropical latitudes this function is performed by birds and mammals. Cereals in meadows, in steppes and savannas, wormwood in deserts, tree species in the tundra and in the middle belt, marsh plants are wind-pollinated. Much less often occurs water pollination (hydrophilia) - it is typical for species whose flowers are blooming under water (for example, zoster). In those climatic zones where one of the above methods is not feasible, self-pollination occurs.

The next stage of reproduction is fertilization andFruit formation. The Department of Angiosperms is characterized by the so-called double type of fertilization. Pollen, caught on the stigma of the pistil, "sprouts", and male reproductive cells move along the pollen tube to the ovule. One sperm participates in the fertilization of the egg, and the other joins one of the cells of a special layer-the embryonic leaf. As a result, in the first case, the embryo is formed, and in the second case, the storage tissue intended for its nutrition is formed.

There is a group of plants that do not require pollination to form fruits (seeds are formed without the participation of pollen). This group includes dandelions, cuffs, some types of buttercups.

There are also plants that reproducepredominantly vegetatively, bypassing the phases of flower formation, pollination and seed ripening. These are bulbous, rhizome and some other representatives of angiosperms.