Output plants on the land, which occurred in the early Silurian (about 435 million. Years ago), accompanied by a number of qualitative evolutionary changes.Plants were forced to adapt to changing conditions of terrestrial life.In the course of evolution they have new tissue (epidermis, xylem, phloem, mechanical tissue) and organs (root and leafy sprout).Eventually primitive Rhyniophyta not have formed shoots were replaced fern species that spread across the world in the Devonian (about 400 mln. Years ago).In the Mesozoic (235-132 mln. Years ago) on a planet dominated by gymnosperms, and behind them there are angiosperms, which are considered the pinnacle of evolution of the plant world.
angiosperms flourishes in the Cenozoic - the geological epoch, which began about 66 million. Years ago and continues to the present.Although, judging by the prints in the rock strata, they have appeared in the Mesozoic (approximately 130 mln. Years ago), but they were few and primitive forms.The oldest angiosperms - Nymphaeales representatives of the group, which include water lilies.
Currently, the department is the most numerous.Between the equator and the two poles there is no area in which there are conditions for plant life, but not found angiosperms.In addition to the widest possible geographical diversity, angiosperms characterized by versatility of forms and methods of growth.Miniature duckweed spanning the surface of the pond, and a huge baobab living hundreds and even thousands of years, prickly cacti and orchids, elegant, modest and daisy giant Rafflesia having flowers meter diameter - they all belong to this department.Quite a large group - aquatic angiosperms inhabiting freshwater (mostly) and salty (less) water.Such species are not primitive, in contrast, is a result of adaptation to the ground forms an aqueous medium.
main feature of angiosperms - the presence of the flower, the generative organs responsible for sexual reproduction and attracts pollinating agents.Hence, the second name of the department - Flowering plants (Magnoliophita).
reproduction of angiosperms is directly related to the process of pollination, which involves insects, birds, mammals, wind and water.In most climates the planet are the main agents of pollination by insects.In tropical latitudes, this function is performed by birds and mammals.Cereals in meadows, steppes and savannas, sagebrush deserts, tree species in the tundra and the middle lane, bog plants are wind-pollinated.Much rarer Water pollination (hydrophilicity) - it is typical for the species, the flowers that bloom under water (eg eelgrass).In those climatic zones where impracticable one of these methods, self-pollination occurs.
next stage of reproduction - fertilization and the formation of the fruit.Department of angiosperms is characterized by so-called double fertilization type.Pollen that gets on the stigma, "sprouts", and the ovule by the pollen tube moving male sex cells.One sperm involved in the fertilization of the egg, and the other is connected to a special layer of cells - embryonic layer.As a result, in the first case, a fetus, and the second - designed for its food storage tissues.
There is a group of plants, which for the formation of the fruit does not require pollination (the seeds are formed without the participation of pollen).This group includes dandelion, lady's mantle, some types of buttercups.
There are also plants that are propagated mainly vegetatively, bypassing the phase formation of flower pollination and ripening seeds.This bulbous, rhizome and some other representatives of the angiosperms.
