Ever wonder what makes lawns so unique to other plants found in the landscape? Ever wonder what makes them so similar? The answers lie in the origins of grasses and their relationships to other plants. While grasses may look different than other flowering plants in the landscape, they may be more similar than you think!
There are almost 400,000 known species of plants in the world with many more getting discovered each year. These plants are categorized through phylogenetics, a system which categorizes plants and other organisms based on their relationships with each other. There are currently 64 orders and 420 families of plants on Earth. These plants and their relationships to each other can be seen here through Flowering Plant Systematics. Grasses are a diverse group of plants belonging to the Poales order and Poaceae family that contains over 12,000 species. Many of these grasses are used for food, fuel, fiber, and yes lawns! Did you know that just 3 species of grasses (wheat, corn, and rice) provide 60 percent of the total plant calories that humans consume worldwide? Wheat, one of the oldest cultivated food crops, can be traced to Egypt as many as 10,000 years ago. Futhermore, many of the world’s most productive farmlands evolved under native grass cover due to its fibrous root system and high carbon sequestration capacity.
The hardiness of grasses can also be seen in perennial lawns and ornamental grasses used in urban and suburban landscapes. Their uniform ground cover and fibrous root system make them ideal for use when it comes to providing ground cover, erosion control, rainwater capture, topsoil remediation, soil arthropod and microbial habitats, and more. They do all of this while at the same time providing a safe place for kids to play and families to enjoy.
There around 10 to 12 species of grasses primarily used for home lawns. While they each differ in their various strengths that make them ideal for a particular use, they also share many common features. One of the most easily observed of these features is their low growth habit and ability to tolerate mowing.
Many grasses tolerate mowing because of the position of their growing point at the top of an un-elongated stem called the crown (Figure 1). This is a region of actively dividing cell tissue that results in the growth of turfgrass leaves, which occurs near the soil surface. As long as vegetative growth continues, newly formed leaves will continue to be formed at the crown and will replace older leaf tissues as they are mowed off of the plant.
As these leaves emerge, they form into two parts; the blade and the sheath. The blade is the unfolded or unrolled part of the leaf while the sheath is the lower portion of the leaf, which attaches it to the rest of the turfgrass plant.
Many fescues and ryegrasses have a bunch-type growth habit while Buffalograss, Creeping bentgrass, St. Augustinegrass, and Centipedegrass have stoloniferous growth habits, and Kentucky bluegrass and some species of Fine fescue have a rhizomatous growth habit. Bermudagrass, Seashore paspalum and Zoysiagrass have both rhizomes and stolons, which is one of the features that often make them hardy in high-traffic settings.
The final and most significant feature of grasses is the inflorescence, or flowering portion of the grass plant (Figure 2). There are many variations of the grass inflorescence, but they are all placed into one of three different categories: the spike, the raceme, and the panicle.
Regardless of the type of inflorescence present in a particular grass species, the basic unit of the inflorescence is the spikelet and the basic unit of the spikelet is the floret. Florets are reduced flowers that can be perfect, staminate, pistillate, or sterile. Lawn grass species have various degrees of self-incompatibility and therefore rely on cross-pollination for fertilization of their flowers. This is one of the factors contributing to the high variability that exists in grasses.
So, while lawn grasses may look different than other flowering plants in the landscape, they really aren’t that different at all. Botanically speaking, lawn grasses are just as much flowering plants as roses, tulips, daffodils, and many trees, but they are just not often thought of this way. First and foremost, many lawn grasses do not produce showy, colorful flowers, which is what many people associate with the term flowers. However, they still possess all of the same reproductive features as other flowering plants including a pistil (stigma, style, ovary) and stamen (anther, filament). In grasses, these structures are compacted into miniature flowers called florets that are small and inconspicuous, so they often go un-noticed.
Lawn grasses have evolved through grazing such that their meristem, or growing point, remains at the soil surface allowing the leaves to be grazed or clipped without killing the plant. This is unlike any other flowering plant found in urban landscapes and is one of the most unique features of grasses. It allows them to persist under mowing and foot traffic while forming a uniform ground cover that is functionally important to the success of many urban landscapes. Simply defined, grasses are flowering plants capable of producing uniform perennial ground cover due to their unique growth habit and there are few, if any, other species of plants that can play a similar role. So get outside and enjoy all the best that lawns have to offer today!