Video: Monocotyledonous plants: origin and characteristics of the class
2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:46
Monocotyledonous plants appeared on planet Earth almost at the same time as dicotyledonous plants: more than a hundred million years have passed since then. But about how this happened, botanists have no consensus.
Proponents of one position argue that monocots are descended from the simplest dicots. They developed in humid places: in reservoirs, on the shores of lakes, rivers. And the defenders of the second point of view believe that monocot plants originate from the most primitive representatives of their own class. That is, it turns out that the forms that preceded modern flowers could have been herbaceous.
Palms, grasses and sedges - these three families took shape and spread by the end of the Cretaceous. But bromeliads and orchids are perhaps the youngest.
Monocotyledonous plants belong to the class of angiosperms, the second largest. They number about 60,000 species, genera - 2,800, and families - 60. Of the total number of flowering plants, monocots make up a fourth. On the border of the 20th-21st centuries, botanists increased this class by crushing several earlierselected families. Thus, for example, distributed lily.
The orchid family turned out to be the most numerous, followed by cereals, sedge, palm. And the smallest number of species is aroid - 2,500.
The generally accepted, widely used throughout the world classification system for monocotyledonous flowering plants was developed in 1981 by the US botanist Arthur Cronquist. He divided all monocots into five subclasses: commelinids, arecids, zingiberids, alismatids and liliids. And each of them still consists of several orders, the number of which varies.
Monocots belong to the Monocotyledones. And in the classification system developed by APG, which gives names to groups exclusively in English, they correspond to the class Monocots.
Monocot plants are represented mainly by herbs and to a lesser extent by trees, shrubs and lianas.
Among them, there are many who prefer swampy terrain, ponds, and propagate with bulbs. Representatives of this family are present on all continents of the globe.
The Russian name for monocotyledonous plants was given by the number of cotyledons. Although this way of determining is neither reliable nor readily available.
For the first time, the English biologist J. Ray proposed to distinguish between monocotyledonous and dicotyledonous plants in the 18th century. He identified the following characteristics of the first class:
- Stems: rarely branching;their vascular bundles are closed; conductive bundles are placed randomly on the slice.
- Leaves: mostly amplexicaul, without stipules; usually narrow; venation arcuate or parallel.
- Root system: fibrous; adventitious roots very quickly replace the germinal root.
- Cambium: absent, therefore the stem does not thicken.
- Embryo: monocotyledonous.
- Flowers: perianth consists of two-, maximum - three-membered circles; the same number of stamens; three carpels.
However, individually, each of these characters cannot clearly distinguish between dicotyledonous and monocotyledonous plants. Only all of them, considered in a complex, allow you to accurately establish the class.
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