Botany - B.E. Yakubenko 2017

Part Three. The Plant Kingdom (Plantae)
Chapter IX. Division Angiosperms, or Flowering Plants (Angiospermae, Magnoliophyta)
Laboratory Session Topic 14.50. The Grass Family, or Poaceae (Poaceae)

General Remarks. The Poaceae family mostly comprises annual and perennial grasses, and more rarely, tree-like forms (such as bamboos). The ROOT System is fibrous, with a rhizome acting as the underground organ. The stems are simple, occasionally branched, slender, cylindrical, featuring nodes and hollow (in most grasses) internodes. The leaves are alternate, arranged in two rows, with a linear (rarely lanceolate) blade and a long sheath embracing the stem. At the junction of the sheath and the blade, There is a ligule in the form of a membranous outgrowth or fringe of hairs. A grass flower consists of upper and lower paleas (floral glumes). The perianth is reduced, represented by two small membranous scales called lodicules, which swell during anthesis to facilitate the opening of the lemmas and paleas. The flowers are bisexual, occasionally unisexual; stamens are typically three, more rarely 2–6 or more, with anthers attached dorsally to the filaments. The pistil is formed by 2–3 fused carpels; the Ovary is superior, unilocular, sessile or short-stipitate; the stigma is bilobed, less commonly 1–3-lobed, feathery. The inflorescence in grasses can be a panicle, raceme, compound spike, or spadix. The compound spike consists of simple spikelets. At the base of each spikelet, there are glumes (1–4) and 1–6 or more (up to 20) flowers. The fruit is a caryopsis, or berry-like in some bamboos. The general appearance of a rye compound spike, flower Structure, diagram of a simple spikelet, and its floral diagram are shown in Figure 111.

Based on their tillering habit, grasses are generally divided into three groups: rhizomatous, loose-bunch, and densely-tufted. Rhizomatous grasses possess both underground and above-ground shoots. The economic importance of grasses is immense, as they form the primary food supply for humanity and play a decisive role in the Nutrition of herbivores. The principal cereal crops include wheat, rice, maize, rye, barley, sorghum, proso millet, oats, and foxtail millet. Wild forage grasses include timothy grass, smooth brome, orchard grass, Sudan grass, crested wheatgrass, meadow foxtail, and ryegrass, among others. Sugarcane is a valuable sugar-yielding grass. Bamboos, reeds, and arundo are utilized as industrial grasses. Barnyard grass, couch grass, crabgrass, annual bluegrass, and others are widespread and troublesome weeds.

The grass family (Poaceae) includes about 700 genera and 10,000 species distributed worldwide. Grasses occupy vast open terrestrial spaces, forming dominant plant communities in the steppes of Europe, the savannas of Africa and Australia, and the prairies of North America.

Evolutionarily, they are closely related to Liliaceae. Sometimes they are regarded as a reduced group of liliaceous plants resulting from a transition to anemophily. The flower of certain tropical grasses (genus Streptochaeta) closely resembles that of Liliaceae in its structure. They possess three lodicules, three floral scales, six stamens arranged in two whorls, and a gynoecium composed of three fused carpels.

Objects:

1. Rye (Secale cereale L.)

2. Perennial ryegrass (Lоlіum реrеnnе L.)

3. Smooth brome (Bromopsis іnеrmis (Lеуss.) Ноlub.)

4. Orchard grass (Dасtylis glomerata L.)

5. Kentucky bluegrass (Роа рrаtensis L.)

6. Couch grass (Еlytrigia repens (L.) Nevski)

7. Meadow fescue (Fеstuca рrаtеnsis Нuds.)

8. Floating mannagrass (Glyceria fluitans (L.) R.Br.)

9. Common reed (Phragmites australis (Cav.) Trin ex Steud.)

Tasks:

1.Examine the specified plants and study the CHARACTERISTICS OF THE family.

2. Using cultivated rye as an example, perform a morphological Analysis of the plant.

3. Identify cultivated rye (determining its family, genus, and species).

Equipment and Materials: dried, fixed, or living plants, identification keys, magnifying glasses, dissecting needles, and methodological manuals.

Macroscopic studies. Cultivated rye is an annual herbaceous plant with a well-developed fibrous root system. The stem is a culm featuring well-developed nodes and hollow internodes. Leaves are linear, with a long tubular sheath clasping the stem, and possess a membranous ligule. The flower is bisexual, consisting of two floral scales: an upper and a lower palea. The lower floral scale (lemma) is about 15 mm long with an awn measuring 2–5 cm. Two floral scales (lodicules) are situated near the ovary, which is superior. There are three stamens. The inflorescence is a compound spike. The spikelets are simple, two-flowered, with two glumes that are shorter than the floral scales, linear-subulate, and awnless. The fruit is a caryopsis.

Following the morphological Description of the plant, proceed with its identification (using the outline provided in the topic).

Key steps for family identification: 1, 9—, 15, 16, 17—, 42—, 47—, 48—, 49, 50—, 51—, 52—, 54, 55—, 57.

Poaceae — Роасеае (Grasses — Grаmineae), p. 55.

Key steps for genus identification: 1—, 2—, 3—, 42—, 43—, 85—, 86—, 87—, 91—, 92—, 93, 94—, 95, 96—, 97. Rye — Sесаlе.

Key steps for species identification: 1—. Cultivated rye — Sесаlе сеrеаlе L.

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Figure 111. Structural Features of the grass flower

Conclusion. Identification of grasses is primarily based on the Morphology of the inflorescence, spikelet, and flower. Attention should be paid to the type of inflorescence, the arrangement of spikelets within it, the number and structure of glumes, the number of flowers per spikelet, the shape of the lemma, and the presence or absence of a keel on it.

Self-Control Questions

1. What is the stem of grasses called?

2. Name the main parts of a grass leaf.

3. What are the floral bracts called and what is their significance?

4. How does a grass flower differ from the flowers of plants belonging to the class Dicotyledones?

5. How many stamens are characteristic of a grass flower, and what are their structural features?

6. What is The structure of the pistil in a rye flower?

7. What is the structure of a single spikelet within complex grass inflorescences?

8. What types of inflorescences are characteristic of grasses?

9. Name the most common types of grasses based on the structure of their underground Organs and tillering node.

10. What adaptations do grasses have for cross-pollination and self-pollination?

11. Name the adaptations of grasses for seed dispersal.