Family cereals determinant. Perennial and annual grass weeds

CEREALS, bluegrass (Gramineae, Poaceae), a family of narrow-leaved monocot plants. This is a very large and complex taxonomic group, in which from two to 12 (now usually recognized 5 or 6) subfamilies were distinguished, uniting approximately 700 genera and 10,000 species. This family includes plants that have a large economic, ecological and historical meaning, specifically wheat, rice, corn, rye, barley, oats, sugarcane, bamboo, and a variety of pasture grasses.

Structure.

According to morphology, cereals are so peculiar that they are described using whole line specific botanical terms.

Stem and leaves.

The stalk of a cereal, called a culm, is usually hollow throughout, except for swollen, regularly spaced nodes, although there are exceptions, such as sugar cane and some species of the bamboo subfamily. The sections of the stem between adjacent nodes are called internodes. As a rule, cereals are herbs, i.e. their fabrics are soft, non-lignified, but tree-like forms are also known, in particular among bamboo ones. The leaves are narrow, with parallel veins, usually sessile, without petiole, one leaves from each node alternately in different sides, located on the stem in two opposite rows.

A typical leaf consists of three main parts: the base, or sheath, covering the stem; a plate bent from the stem; a small membranous or hairy outgrowth - a tongue (ligula) that separates the vagina from the plate. The leaves of some cereals have ears - paired, usually lobed, sometimes lanceolate or sickle-shaped lateral outgrowths at the junction of the plate and sheath.

Roots.

The root system of cereals is fibrous, i.e. without a main central axis, formed by numerous thin roots, a bundle extending from the lower part of the stem. By origin, they are adventitious, as are the supporting roots, which begin in some cereals even above the ground. The fixation of a plant in the soil is often facilitated by tillering - the formation of many basal shoots that make up a loose or dense, tussock-like turf. Usually the roots account for the bulk of the cereal, sometimes up to 90%. Such 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, inconspicuous, without a distinct perianth. The petals and sepals are represented by one or more miniature scales, which are called flower films, or lodicules, and are located under the stamens. The flower is usually bisexual, i.e. contains both stamens and pistil. The pistil consists of an ovary with two (rarely three) columns bearing long feathery stigmas. There are usually three stamens - with long filaments hanging from the flower and oblong anthers.

These parts are surrounded by scaly bracts, i.e. small, highly modified leaves. Usually, they distinguish between the upper, narrower, lemma and the lower lemma, which is larger and sometimes embraces the upper one. The reproductive parts, the lodicules, and these scales form a compact structure called a flower in cereals. The flowers are located in two opposite rows on the thin axis of the spikelet, at the base of which there are two modified covering leaves of the inflorescence - glumes. They, like the lower lemmas, are pointed at the top or elongated into an awn, sometimes very long. Flowers on the spikelet axis with spikelet scales form a compact inflorescence - a spikelet. From this general scheme deviations are possible: in some species, spikelets are single-flowered, only one of the spikelet scales remains 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 raceme (spikelets on short legs) or an ear (spikelets are sessile). However, most cereals main axis inflorescence branches and spikelets are on its side branches. Such a complex brush is called a panicle.

Fetus.

The ovary in cereals is single-celled, 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 an embryo containing nutrients endosperm and seed coat, which fuses with the wall of the ovary (pericarp); this is how a characteristic cereal fruit is formed, called a caryopsis or, in everyday life, simply a grain, for example, wheat, corn, etc. It differs from fruits of another type by a very thin pericarp, practically inseparable from a single seed.

Grass-like plants: sedge and rush.

For damp habitats, two families of plants are characteristic - sedge (Cyperaceae) and rush (Juncaceae), the species of which are often confused with cereals due to their external similarity.

However, sedges differ from grasses in several distinct features. The stalk of cereals is knotty, usually hollow in the internodes and round in cross section. In sedges, it is without nodes, usually incomplete and triangular in cross section. Leaf sheaths in cereals, as a rule, are not fused at the edges and are easily separated from the stem; in sedge - closed, very firmly covering it. The leaf arrangement in cereals is two-row, in sedge - three-row. Flowers in sedges, like in cereals, are devoid of perianth and collected in spikelets, however, each flower is protected not by two, as in cereals, but by one bract, and the spikelets often form an umbrella-shaped inflorescence, i.e. are at the ends of the legs emerging from one point at the top of the stem. Finally, the sedge fruit is a nut or achene: its pericarp does not grow together with a single seed.

In rushes, the stems are without nodes, non-hollow, round in cross section. Leaves usually grow only from their base. The vagina is open, but there is no tongue, and the leaf blade is cylindrical. The flowers are small and inconspicuous, but with six identical scaly perianth elements arranged three in two circles. The inflorescences are in principle cymose, i.e. the first flower opens at the top of the central axis, and then the rest - on the branches extending below it, however, outwardly they may look like panicles, brushes, etc. The fruit is not a caryopsis or achene, but a three-celled or one-celled box with small seeds, which opens and scatters them when ripe.

In addition to sedges, reeds belong to the sedge family (genus Scirpus). This word is also often incorrectly used to refer to species of cattails growing in damp places from a completely different family (Typhaceae). Of the economically important, at least in antiquity, papyrus deserves mention ( Cyperus papyrus).

The role and use of cereals.

Since ancient times, cereals have been the basis of human and livestock nutrition. About $18 billion worth of corn alone is produced annually in the United States. Much of that country's farmland is grazing with fodder cereals or grass mixtures (mixed crops of cereals and legumes), which provide more than a third of the fodder needed by livestock. On the importance of corn and other food grains such as oats, millet, wheat, rice, rye, sorghum, cm. related 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. They not only build houses, bridges and fences, but also make mats, vessels, and decorative objects. In the old days, they were also needed for making spears and arrows.

Erosion control.

Erosion and reduced soil fertility have become global issues. Grains help to solve it. For example, in the US, they are used along with other seaside grasses to anchor sand dunes. The cereals sown on them usually have long rhizomes (underground stems) and tough, elastic leaves that can withstand the blows of wind-blown sand.