Gramineae, or Poaceae - grass family
Belong to liliids (Liliidae, monocots). 8, 000 species distributed throughout the world, but most genera concentrate in tropics. Prefer dry, sunny places. Of-ten form turf (tussocks)—compact structures where old grass stems, rhizomes, roots, and soil parts are intermixed. Grasses form grasslands—specific ecological communities widely represented on Earth (for example, North American prairies are grasslands). Stems of grasses are usually hollow and round. Leaves with sheaths.
Flowers reduced, wind-pollinated, usually bisexual, form complicated spikelets. Each spikelet bears two glumes; each flower has lemma and palea scales (Fig. 8.21). Perianth is reduced to lodicules. Stamens from 6 to 1 (most often 3), with large anthers. Flower formula is
Fruit is a caryopsis; it includes flower scales. Seed contains embryo with coleop-tile, coleorhiza and scutellum (Fig.7.15).
Most primitive grasses are bamboos (Bambusoideae subfamily). There are many other subfamilies. Two are especially economically important:
• Pooid (Pooideae) grasses usually are C3 plants, wheat (Triticum), rice (Oryza), barley (Hordeum) and rye (Secale) belong to this group.
• Panicoid (Panicoideae) grasses are mostly C4 plants, corn (Zea), sorghum (Sorghum) and sugarcane (Saccharum) belong here.