The grasses are a very large family of plants that have narrow leaves and are usually herbaceous. There are about 3,500 species of grasses, called graminoids, as well as many more varieties and cultivars. The family includes rushes and sedges as well as the true grasses, and the true grasses include cereals and bamboo as well as the wild grasses of natural grasslands and the cultivated grasses of turf or lawns. All grasses reproduce by seed.
Like the seeds of all flowering plants, formally named angiosperms, grass seed contains the embryo of a new plant. It also contains nourishment for the embryo to live on during the germination process. The external surface protects the seed until germination.
The embryo is basically a version of the plant in extremely immature form. The embryo has several parts and will grow from two points. The radicle, when it begins to grow, orients itself toward gravity and grows downward; it develops into roots. The plumule grows upward, becoming a shoot. Attached to the shoot is a cotyledon, or seed leaf. The area of the plumule above the cotyledon is the epicotyl; when it is exposed to sunlight, it will sprout true leaves so that photosynthesis can take place. The area of the plumule below the cotyledon is the hypocotyl.
All angiosperm seeds contain cotyledons, or seed leaves. Although they look like true leaves, they cannot photosynthesize. Like other monocotyledons, grass seed embryos have only one cotyledon. This compares to two cotyledons for dicotyledons and multiple cotyledons for gymnosperms.
The endosperm is the part of the seed that contains nourishment for the growing embryo. The two proteins that make up gluten are found in the endosperm of wheat, rye and barley.
In the grasses, the seed coat is typically fused to the fruit. Although this fused structure is often casually called a seed, it is more correctly named a pericarp. It is also sometimes called a kernel, like a kernel of corn. The cereal grasses typically produce rather large fruits, while the turf grasses produce small ones.
Seed Dispersal Structures
Grass seeds are dispersed in various ways. Those with large fruits are typically eaten by animals and birds, and the seed is deposited at a distance. Some of the turf grass seeds have slightly hairy external structures, while others have awns, small hooks attached at the base. These structures make it more likely that the seed will become caught in the fur of passing animals and carried for a distance.