True grasses, those used for lawns and turf, are members of the Poaceae family of plants. Grasses of the Gramineae family of plants include rice, wheat, oats, barley and other grasses that produce cereals, grains, flour and straw. Other types grasses include rushes and sedges found in grasslands and marshes. The grass structures listed here are those of grasses commonly used for lawns, playing fields and golf courses.
Culms are the main axis, or above ground stems from which grass leaves grow. Culms are usually round and hollow; they are interrupted at intervals by swollen joints called nodes. Grass stems are rarely branched. Nodes can be seen clearly on bamboo culms; bamboo is a kind of grass.
Leaves grow from the nodes of culms. A protective sheath opens to make way for the growing blade; a small membrane or flap called the ligule is located where the blade emerges. On some grasses, the ligule is flanked by projections called auricles. Leaf blades are ordinarily narrow and long with veins and sides that are parallel; they taper to a blunt or pointed tip.
Grass spreads by runners, or horizontal stems, that run both beneath and above ground.
Rhizomes are underground stems that branch out horizontally. Rhizomes have nodes similar to that found on culms. New shoots, called tillers, grow from the nodes of rhizomes. Tillers become new, above-ground culms.
Stolons are above ground stems that branch out horizontally. They also have nodes from which new tillers grow.
Florets grow on an axis or stem called the rachilla; florets do not have sepals or petals. Scales at the base of the rachilla, called glumes, protect the young florets; each floret is enclosed by two sets of protective scales, the lemma and the palea.
Grass florets are bisexual, having one female ovule or ovary ordinarily flanked by two feathery stigmas that receive pollen. The ovule and stigma are surrounded by three stamens, the male part of the flower; each stamen has a pollen-bearing anther on top of a filament.
Spikelets contain two more florets. Spikelets are arranged into an inflorescence or flower head in different ways, depending on the species. A spikelet on a stalk growing from a culm or main axis is called a panicle. A spikelet on a stalk growing from a branch of a culm is called a raceme. A spikelet with no stalk that grows directly from the culm is called a spike.