Monocotyledonous plants: the origin and characteristics of the class

Monocotyledonous plants on the planet Earth appearedalmost at the same time as dicotyledons: since that time more than one hundred million years have passed. But about the way it happened, the botanists do not have a common opinion.

Supporters of one position argue thatmonocotyledons descended from the simplest dicotyledons. They developed in wet places: in water bodies, on the shores of lakes, rivers. And the defenders of the second point of view believe that monocotyledonous plants originate from the primitive representatives of their own class. That is, it turns out that the forms preceding the modern flowers could be herbaceous.

Palm, cereals and sedge - these three families have formed and spread already towards the end of the Cretaceous period. But bromeliads and orchids, perhaps, are the youngest.

Monocotyledons belong to the classangiosperms, the second largest. They count about 60 000 species, genera - 2 800, and families - 60. Of the total number of flowering plants, monocots make up a fourth. At the border of 20-21 centuries, botanists increased this class due to the fragmentation of several previously isolated families. Thus, for example, the lily was distributed.

The most numerous was the orchid family, followed by cereals, sedge, palm. And the smallest number of species counts the aroids - 2,500.

Common, widely used all over the worldIn 1981, the botanist from the United States, Arthur Kronkvist, developed the system for the classification of monocotyledonous flowering plants. He broke all monocotyledons into five subclasses: comelinids, arecids, zingiberides, alismatids and lilies. And each of them still consists of several orders, the number of which varies.

Monocots are Monocotyledones. And in the classification system developed by APG and giving names to groups exclusively in English, they correspond to the Monocots class.

Presented primarily monocots herbs and to a lesser extent - trees, shrubs and vines.

Among them, many are those who prefer swampy terrain, ponds, bulbs multiply. Representatives of this family are present on all continents of the globe.

Russian monocotyledonous plants were given by the number of cotyledons. Although this method of determination is neither reliable nor readily available.

The first to distinguish between monocotyledonous and dicotyledonous plants was proposed in the 18th century by the English biologist J. Ray. He defined the following characteristics of the first class:

- Stems: rarely branching; their vascular bundles are closed; The conducting beams are arranged randomly on the cut.

- Leaves: mostly stems, not having stipules; as a rule, a narrow form; venation is arcuate or parallel.

- Root system: fibrous; the accessory roots very quickly replace the embryonic rootlet.

- Cambium: is absent, therefore the stem does not thicken.

- Embryo: monocotyled.

- Flowers: perianth consists of two, maximum - three-membered circles; the same number of stamens; three carpels.

However, individually, each of these features can not clearly distinguish between bipartite and monocotyledonous plants. Only all of them, considered in the complex, allow to establish the class unerringly.