Poaceae: (Gramineae) Grass Family
Distributed throughout the world wherever vascular plants can survive. It includes about 600 genera, 10,000 species. In Pakistan it is represented by 158 genera and 492 species.
The traditional family name Gramineae takes its name from the latin Grammar which was used as a ‘ generic’ name for certain grasses, is permitted by the International Code of Binomial Nomenclature, which also provides for the use of Poaceae, based upon they type genus Poa Linn.
Familiar Plnats: Triticum vulgare, Wheat; Zea mays, Corn; Avena Sativa, Oats; Oryza sativa, Rice; Bambusa, Bamboo; Saccharam officinarum Sugar Cane etc.
Vegetative Characters: habit: annual or perennial, herbs. Stem: jointed usually hollow at the internodes, closed at the nodes. Leaves: solitary at the nodes, sometimes crowded at the base of the stem, alternate. Exstipulate, ligulate, mostly sessile, leaf-base mostly sheathing, simple.
Inflorescence: mostly compound composed of units called spikelets which are variously arranged (indense clusters as in wheat, compound spike, or loosely on branched axis-as in oats, spikelets consisting of bracts, arranged along a slender axis (called rachilla) the two lower bracts (called glumes) which are empty: the succeeding lemmas enclosing a flower and opposed by a hyaline scale called palea. The whole (lemma, palea, and flower) termed as floret: the glumes or lemmas often bearing one or more stiff bristles (called awns); this basic pattern of spikelet structure is consistent throughout the family. Spikelets of grasses vary widely in different genera, particularly as to number of fertile florets in each, and deposition of sexes with them.
Flowers: Usually bisexual, sometimes unisexual, small and inconspicuous, sessile, bracteates, incomplete, zygomorphic, hypogynous. Perianth: Absent or represented by 2, (rarely 3), minute hyaline or fleshy scales called lodicules. Androecium: Stamens 1 to 6, usually 3. With – delic compound pistil of 3 united carpels, anthers versatile through only one is functional free stigmas usually large feather like. Fruit: graius or caryopsis (caryopsis a dry, indehiscent fruit in which fruit wall (percarp) is completed, fused with seed coat).
Economic Importance: Economically family Poaceae has greater importance than any other family of flowering plants. It has great economic importance to both man and animals. Cereals and millets which constitute the chief food stuff of mankind, belongs to this family. Most of the fodder crops, which are equally important to domestic animals, also belong to this family.
Plants providing food for man includes: Triticum sp. (wheat), Avena sativa (Oats), Zea mays (Corn, Maize), Oryza sativa (Rice), Hordeum vulgare (barley), Secale cereal (Rye), Penisetum typhoideum; Sorghum vulgare etc.
The dried stem and leaves of the cereal crops are used as fodder for the cattle. Sugar is obtained from the juice of Saccharum officinarum (Sugar Cane). Many grasses are used in the lawns e.g. Agrostis, Poa, Festuca etc. and have ornamental significance.
Fig. 9.30 Poaceae (Gramineae): Chloris barbata: A habit; B-spikelet: C-gulumes: D-fertile lamma, E-flower: F-fruit;
Bambusa (Bamboo) are used as building material for the thatching huts, making boats, carts, pipes etc. and the split stem are woven into mats, baskets, fans, hats, course umbrella. Leaves are also given to horses as a cure of cough and cold etc. certain grasses yield aromatic oils, e.g. Cymbopogon citrates (lemon grass) which yield lemon grass oil is used in perfumes and soap industry and for making infusions. Some species of the grasses are used in making papers.
Ethyl alcohol and many other kind of beverages are also prepared from cereals for example whisky from Rye, barley, corn and rum molasses from sugar cane. Fibers obtained from the leaves of Saccharum munja which is used in making ropes.