The Structure of Grass Leaves

Mowing keeps grass plants from fully developing.

A blade of grass is rarely thought of as belonging to an individual plant. Mowing lawn grass keeps it from fully developing as nature intended it, and it rarely appears as anything more than the densely packed trimmed growth known as blades, which are actually the plants' leaves. But when left to develop to its full size, such as in hay fields and on prairies, a grass plant is composed of many of the same parts as other plants.

Grass Plant Anatomy

If allowed to grow to maturity, a grass plant is composed of a fibrous root system; a shoot, or stem; a blade, or leaf that is veined with a central fiber called a midrib; a sheath and sheath node where a new leaf emerges and wraps itself around the stem; a collar; a spikelet; and finally, a seedhead. The collar is the narrow section of tissue that connects the leaf to the sheath, and is usually a lighter green than the rest of the grass plant. A ligule is another small bit of tissue that holds the leaf and sheath to the stem. Emerging grass leaves are either rolled or packed inside the buds, and they are rough or smooth depending upon their species.

Germination

When a grass seed germinates, it sends up one shoot and a single leaf, or blade from its crown, which is a white knob located just above the surface of the soil. The fibers in each leaf run in a parallel pattern from the crown to the tapered tip of the blade. As the crown pushes the new leaves up, they unfurl and wrap themselves around the shoots, forming a sheath. This pattern differs from that seen in other types of plants that produce growth from the tips of stems or branches. It is this feature that makes it possible to keep grass cut without limiting its growth.

Growth Habits

The visible parts of grass plants emerge from crowns that grow at ground level. If grass is grown from seed, each seed produces one blade that unfurls from a small stem just above the crown. Grass leaves live for roughly 40 days before dying back and making way for new growth, called tillers, that continue to emerge from healthy crowns that have not been affected by mowing or disease. Eventually, the roots also die back and are replaced with new ones. Healthy lawns develop the thick lush appearance when the tiller replacement rate begins to exceed the die-back rate of old grass.

Spreading Habits

Grasses spread by sending out stolons, rhizomes or by producing tillers. Stoloniferous grasses, such as bentgrass, produce stems that creep across the ground and take root near the parent plant. Ryegrass and fescue are examples of grasses that multiply by producing multiple tillers, or new leaves, from their crowns. Grass that sends out rhizomes, or below-ground runners, produce new plants at a considerable distance from the mother plants. Kentucky bluegrass spreads in this manner, producing thick, even growth with upright shoots and leaves.

References

• Lawn Care Academy; Plant Structure Reveal Keys To A Better Lawn; 2011
• University of Minnesota; Grass Plant Structure and Growth; 2006
• Texas A&M University; Using Plant Structures As A Key; Paul A. Baumann
• University of Georgia: Parts Of A Grass Plant
• Michigan State University: Forage Grass Identification