The family of cereal determinant. Perennial and annual cereal weeds

CEREALS,bluegrass (Gramineae, Poaceae), a family of narrow-leaved monocotyledonous plants. This is a very large and complex taxonomic group, in which from two to 12 (usually 5 or 6 are recognized now) subfamilies, uniting about 700 genera and 10,000 species. This family includes plants of great economic, ecological and historical importance, in particular wheat, rice, corn, rye, barley, oats, sugar cane, bamboo and a variety of pasture grasses.

Structure.

In terms of morphology, the cereals are so peculiar that a whole number of special botanical terms are used to describe them.

Stalk and leaves.

A stalk of cereal, called a straw, throughout, except for swollen, separated by regular intervals of nodes, usually hollow, although there are exceptions, such as sugar cane and some types of bamboo subfamily. Stems between adjacent nodes are called interstices. As a rule, cereals are herbs, i.e. their fabrics are soft, non-ligneous, but tree forms are also known, in particular among bamboo ones. The leaves are narrow, with parallel veins, usually sessile, without a stalk, depart one at a time from each node alternately in different directions, settling on the stalk in two opposite rows.

A typical leaf consists of three main parts: the base, or vagina, covering the stem; plate bent from stem; small membranous or hairy process - uvula (Ligula) separating the vagina from the plate. The leaves of some cereals have ears - paired, usually lobed, sometimes lanceolate or sickle-shaped lateral processes at the junction of the lamina and the vagina.

Roots.

The root system of cereals is fibrous, i.e. without the main central axis, formed by numerous thin roots, a beam extending from the bottom of the stem. By origin, they are adventitious, as well as supporting roots, beginning in some cereals even above the ground. Tillering often contributes to the fixation of a plant in the soil - the formation of a multitude of basal shoots that constitute loose or dense, hummocky turf. Typically, the roots account for the bulk of the cereal, sometimes up to 90%. Such a root system, which effectively absorbs and accumulates water, helps to survive in conditions of regular grazing by herbivores, periodic droughts and steppe fires.

Flowers

The flowers are small, hardly noticeable, without a distinct perianth. Petals and sepals are represented by one or more miniature scales, which are called flowering films, or lodicules, and are located under the stamens. The flower is usually bisexual, i.e. contains both stamens and pistils. The pistil consists of an ovary with two (more rarely three) columns carrying long feathery stigmas. There are usually three stamens - with long filaments hanging from a flower and oblong anthers.

These parts are surrounded by scaly bracts, i.e. small, highly modified leaves. Usually, they distinguish the upper, narrower, flowering scales and the lower flowering scales, which are larger and sometimes embrace the upper ones. Reproductive parts, lodicules and these scales form a compact structure called a flower in cereals. The flowers in two opposite rows are located on a thin axis of the spikelet, at the base of which there are two modified covering leaves of the inflorescence - spikelet scales. They, like the lower floral scales, at the top are pointed or extended into an awn, sometimes very long. Flowers on the spikelet axis with spikelet scales form a compact inflorescence - spikelet. Deviations from this general scheme are possible: in some species, spikelets are single-flowered, spikelet scales are left with only one or they are completely absent, etc.

Spikelets, in turn, are attached to the larger axis of the complex inflorescence. If this axis is simple, the inflorescence is called a brush (spikelets on short legs) or an ear (spikelets are sessile). However, in most grasses, the main axis of the inflorescence is branched and spikelets are on its side branches. Such a complex brush is called a whisk.

Fetus.

Ovary in cereals single-nest, i.e. it contains a single cavity with an ovule. After pollination and fertilization of the egg in the ovule, the latter matures into a seed with a germ that contains nutrients endosperm and the seed coat, which grows together with the wall of the ovary (pericarp); this is the way the characteristic fruit of the cereal is formed, called grains or in everyday life just grains, such as wheat, corn, etc. It differs from fruits of another type by a very thin pericarp, which is almost inseparable from a single seed.

Cereal-like plants: sedge and rush.

For wet habitats are characterized by two families of plants - sedge (Cyperaceae) and rush (Juncaceae), species that are often confused with cereals due to external similarities.

However, sedge differ from cereals in several distinct signs. The stem of cereals is knotty, usually internally hollow and round in cross-sections. In sedges it is without nodes, usually incomplete and triangular in cross section. Leaf sheaths in cereals, as a rule, not fused edges and easily separated from the stem; sedge - closed, very firmly covering it. The leaf arrangement in cereals is two-rowed, in sedges - three-row. Flowers in sedge, like in grasses, have no perianth and are collected in spikelets, but each flower is protected not by two, like in grasses, but by one bract, and spikelets often form an umbellate inflorescence, located at the ends of the legs extending from one point on top of the stem. Finally, the fruit of the sedge - nut or achene: its pericarp does not grow together with a single seed.

In Sitnic stems without nodes, incomplete, round in cross section. Leaves usually only move away from their base. The vagina is not closed, but the tongue is not, and the leaf blade is cylindrical. The flowers are small and inconspicuous, but with six identical scale-like perianth elements, located three in two circles. Inflorescences are in principle cymotic, i.e. the first flower opens on top of the central axis, and then the rest - on the branches extending below it, but externally may look like panicles, brushes, etc. The fruit is not a kernel or seed, but a three-nest or single-nest box with small seeds, which opens and disperses them when ripe.

The sedge family, in addition to sedges, includes reed (genus Scirpus). This word is often incorrectly also referred to as species of rogyz growing in damp places from a completely different family (Typhaceae). Of the economically important, at least in antiquity, sedge deserves a mention of papyrus ( Cyperus papyrus).

The role and use of cereals.

Since ancient times, cereals have formed the basis of nutrition for people and livestock. In the United States, only corn for about $ 18 billion is produced annually. A significant part of the agricultural land in this country is used for pastures with feed grasses or grass mixtures (mixed crops of cereals and legumes), which provide more than a third of the feed needed for cattle. The importance of corn and other food grains, such as oats, millet, wheat, rice, rye, sorghum, cm. relevant articles.

Bamboo is widely used in construction. Its woody stems reach a height of more than 30 m with a diameter at the base of 20-25 cm. Of them not only build houses, bridges and hedges, but also make mats, vessels, decorative objects. In the old days they were also needed for making spears and arrows.

Fight against erosion.

Erosion and soil fertility decline have become global issues. Cereals help solve it. For example, in the USA, they are used with other seaside grasses to anchor sand dunes. The grasses planted on them usually have long rhizomes (underground stems) and rigid elastic leaves that withstand the blows of the sand lifted by the wind.