The emergence of plants on land that occurred at the beginning of the Silurian 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-stem shoot and root). Over time, primitive rhinophytes that do not have formed shoots gave way to 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, which are considered the peak of the evolution of the plant world.
Angiosperms flourish in the Cenozoic, a geological era that began about 66 million years ago and continues to the present. Although, judging by the prints in the rock strata, they appeared in the Mesozoic (about 130 million years ago), but these were not numerous and primitive forms. The oldest angiosperms are representatives of the nymphaea group, which include water lilies.
This department is currently the most numerous. There is no such section between the equator and both poles where conditions for plant life exist, but angiosperms were not found. In addition to the widest geographical diversity, angiosperms are characterized by the versatility of forms and methods of growth. A miniature duckweed that captures the surface of the reservoir, and a huge baobab that lives for hundreds and even thousands of years, prickly cacti and elegant orchids, a modest chamomile and giant rafflesia with flowers of a meter diameter - all of them belong to this section. A rather large group is the aquatic angiosperms that inhabit 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 presence of a flower, a generative organ responsible for sexual reproduction and attracting pollination agents. Hence the second name of the department - Flowering plants (Magnoliophita).
Propagation of angiosperms is directly related to the pollination process, which involves insects, birds, mammals, wind and water. In most climatic zones of the planet, the main pollination agents are insects. In tropical latitudes, this function is performed by birds and mammals. Cereals in meadows, in the steppes and savannahs, wormwood in the deserts, tree species in the tundra and middle strip, marsh plants are wind-pollinated. Water pollination (hydrophilia) is much less common - it is typical for species whose flowers bloom under water (for example, zoster). In those climatic zones where one of the listed methods is not feasible, self-pollination occurs.
The next stage of reproduction is fertilization and the formation of fruits. The Angiosperms department is characterized by the so-called double type of fertilization. The pollen that has fallen on the stigma of the pestle “sprouts” and male reproductive cells advance into the ovule along the pollen tube . One sperm is involved in the fertilization of the egg, and the other connects to one of the cells of a special layer - the germ layer. As a result, in the first case, the embryo is formed, and in the second, the storage tissue intended for its nutrition.
There is a group of plants that does not require pollination to form fruits (seeds are formed without pollen). This group includes dandelions, cuffs, some types of buttercups.
There are also plants that multiply mainly by the vegetative method, bypassing the phases of flower formation, pollination and seed ripening. These are bulbous, rhizome and some other representatives of angiosperms.