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Guide to Texas Grasses

Texas A&M University Press

WHY GRASSES ARE IMPORTANT

The Poaceae (Gramineae) consists of approximately 785 genera and 11,000 species (Watson and Dallwitz 1992; Chen et al. 2006). Based on genera, the grasses are the third-largest family of flowering plants after the Asteraceae (sunflowers) and Orchidaceae (orchids). Grasses are fifth in the number of species behind the Asteraceae, Fabaceae (legumes), Orchidaceae, and Rubiaceae (madders) (Good 1953). Two-thirds of the earth's land surface is used for grazing, and one-third is composed of grasslands (Schantz 1954). Grasses occur on every continent and within nearly every terrestrial ecosystem. Hartley (1954) estimates that there are more individual grass plants than all other vascular plants combined. Based on completeness of representation in all regions of the world and percentage of the world's vegetation, grasses far surpass all other plant families (Gould and Shaw 1983). The economic, ecological, and geographic importance of grasses cannot be overestimated or overemphasized (Clark and Kellogg 2007).

Food for Human Consumption

The cereal grains (barley, corn, millet, oat, rice, rye, sorghum, wheat) supply the bulk of food that humans consume (fig. 1.1a). Rice feeds more people than any other food product. Wheat cultivation covers more area than any other crop. No crop covers a wider geographic range than corn. A major portion of the world's sugar comes from sugarcane (Saccharum officinarum). Even the "woody" grasses are a source of nutrition (bamboo shoots and caryopses during mass flowering).

The major dietary substance found in grass caryopses is carbohydrates. These carbohydrates are stored in the endosperm, nutritive tissue used during seed germination and seedling establishment, which along with the embryo forms the major part of the grass caryopsis. The seed containing the endosperm is of most value to humans. From the seed comes flour, corn meal, rice, oats, and intoxicants (beer, rice and barley wine, corn and rye liquor, etc.). For this reason all cereal species are almost exclusively annual plants. Annuals put most of their energy into reproduction (more seeds) rather than roots and/or vegetative structures, which die at the end of the growing season. Humans harvest and put to multiple uses the seeds that ensure propagation of the annual species. Carbohydrates in the endosperm are the substance upon which most civilizations have developed and been maintained. The ability of farmers to feed many individuals, not just themselves and their families, allows others to pursue such activities as the arts, manufacturing, trade, education, bureaucracies, and, alas, war—all the fabric of human civilizations. The classic example of endosperm is the large, white, "exploded" portion of a piece of popcorn. The soft, sweet portion of a partially popped kernel, sometimes referred to as "old maids" or "duds," is the embryo. The golden covering of the endosperm and embryo, which more often than not gets stuck between one's teeth, is the seed coat.

Grasses and grass by-products dominate the Texas agricultural economy. Over $4.5 billion in grass crops (hay [dry and silage], grain [corn, rice wheat, sorghum], sugar) is produced annually (fig. 1.1b). More land is used for hay, grass silage, and greenchop in Texas than in any other state (5 million acres). Texas ranks second in sorghum for grain and total value of agricultural products sold (USDA-NASS 2007).

Forage for Wild and Domestic Animals

The majority of large herbivores characteristic of the expansive grasslands of the world are dependent upon grasses as a major portion of their diet. Humans, in turn, depend upon wild and domestic herbivores as a major source of protein and nutrients in the form of meat, blood, and milk (fig. 1.1c). These animals are also significant as the source of leather (hides) and animal fiber (wool, mohair, etc.).

In Western societies large infrastructures have been developed to supply these animal products to an ever-enlarging and demanding population. Corn and sorghum silage is harvested for livestock in feedlots. Also, much of the corn, millet, and sorghum grain is used as feed for cattle, swine, and poultry.

Over 14 million head of cattle and calves and 1 million sheep are maintained on Texas rangelands and feedlots. Texas ranks first among the states in value of livestock, poultry, and their products; cattle and calves; and sheep, goats, and their products. Cash receipts of over $11.3 billion were from livestock or livestock-related products in Texas in 2006 (USDA-NASS 2006). All these animals survive primarily on grasses and grass products.

While it is easy to envision the role and importance of grasses to the large herds of herbivores that once occupied the grasslands of Africa, Eurasia, and North America, one often forgets about the importance of grasses to other wildlife. There are many graminivorous upland birds and small mammals. Also, grasses compose a significant portion of waterfowl diets. Mannagrasses (Glyceria), cutgrasses (Leersia), and wildrices (Zizania, Zizaniopsis) are of special importance to birds that utilize swamps, lakes, and marshes. Some migratory birds not only use wetlands dominated by grasses but also overwinter on grain fields and pastures (Gould and Shaw 1983).

Soil Conservation and Land Improvements

A majority of the world's most productive soils now used for grain production were developed under perennial grassland cover (Gould and Shaw 1983). Removal of this native, perennial grass cover by plowing or poor grazing management has led to both wind and water erosion, and a large amount of topsoil has been lost over the centuries. Reestablishment of a perennial grass cover is a common practice in soil conservation and range improvements. A "good" cover of grasses not only stabilizes the site, reducing erosion, but helps in replacing depleted nutrients from overutilized soils. Numerous state and federal agencies developed during the twentieth century to assist landowners in reducing erosion and returning lands to a more productive and economically viable state. Specific industries have developed that focus on improving the condition of rangelands and restoring other disturbed sites (land rehabilitation, mine reclamation).

Some grasses adapted to restricted ecological niches have been used for specific erosion control purposes. For example, vetiver (Vetiveria) is used extensively in southern Asia and Oceania for erosion control and terrace production (National Research Council 1993). Beachgrass (Ammophila) with its extensive rhizomes has been used to stabilize sand dunes. The same is true for the native blowout grass (Redfieldia flexuosa), which is used to stabilize shifting sands of the Great Plains region.

Turf and Ornamentals

Often overlooked, but not insignificant, is the use of grasses for turf and ornamentals. Grasses with rhizomes, stolons, or both (sod formers) have been used for centuries to produce a dense, thick cover that will resist use (primarily foot traffic) and be aesthetically pleasing (generally of uniform color and density) (fig. 1.1d). Most common uses of turf grasses are for lawns, parks, highway rights-of-way, golf courses, and athletic fields of all sorts (Gould and Shaw 1983). Maintenance of turf supports a multi-billion-dollar industry supplying seed, fertilizer, herbicides, insecticides, specialized machinery, sprinklers, hoses, and so on, as well as lawn care services. In Texas major turfgrasses recognized by most people are St. Augustine (Stenotaphrum secundatum), bahiagrass (Paspalum notatum), Bermudagrass (Cynodon dactylon), zoysia (Zoysia japonica), buffalograss (Buchloë dactyloides), centi-pedegrass (Eremochloa ophiuroides), ryegrass (Lolium multiflorum), and Kentucky bluegrass (Poa pratensis). Included in this book are the many turfgrasses that have escaped cultivation and occur as permanent members of Texas grass flora.

Recently, grasses have become much more popular as ornamentals. Bamboos (e.g., Bambusa, Phyllostachys) have traditionally been cultivated, but now many herbaceous grass species are being incorporated into human landscapes (fig. 1.2a, b). This popularity is based on the relative cost-effective propaga ion of herbaceous grasses, their ease of maintenance, adaptability to a wide range of soil textures and nutritive levels, and versatility. Their uses can vary from ground cover; single-specimen plants such as Erianthus (Saccha-rum) and Miscanthus; mass planting (Festuca, Pennisetum); and erosion control. Historically, mostly exotic, introduced grasses were used as ornamentals, but native species (e.g., Panicum, Andropogon, Sorghastrum, Chondrosum, Boute-loua) are becoming more and more popular.

Biofuels

As the world's petroleum supply diminishes and/or is controlled by unstable and/or hostile governments, many countries are developing alternative energy sources. The four major alternatives are solar, wind, geothermal, and biological energy. Use of alternative energy sources also reduces greenhouse gas emissions, which in turn assists in mitigation of global climate change. Ethanol, sometimes referred to as grain alcohol, is a primary bio-energy source. It has long been known as a product of fermentation and distillation. Etha-nol is now being used as an additive to gasoline, and the newer flex vehicles are capable of using up to 85% ethanol. Corn and sugarcane are the most commonly used plants for ethanol production. Of the world's projected 12 billon bushels of corn produced in 2007, some 3.2 billion bushels, or 26%, will be used for ethanol production. However, production from sugar-based ethanol yields 8 times more alcohol per acre than corn does. There are certain to be social consequences and conflicts between developed and underdeveloped countries when people are starving and crops are being used for fuel rather than food. If every kernel of corn produced in the United States were used to produce ethanol, only about 15%–20% of our current petroleum consumption could be met. Obviously, production of bioenergy from grains is only a temporary solution to the energy problem.

Cellulosic biomass has the potential to diminish the demand for petroleum and increase bioenergy while reducing the conflict between food and fuel. Bioenergy from cellulosic biomass uses the carbon within the cellulose and hemicellulose of plant cell walls to produce biofuels, again primarily ethanol. Cellulosic biomass can come from municipal waste, forest waste products (slash), crop residue (corn stover), native herbaceous vegetation, and "designer" crops such as cultivars of switchgrass (Panicum virgatum) and giant sorghum (Sorghum bicolor) (fig. 1.2c). Although this is still an emerging industry, it has great potential to help the environment while meeting a significant portion of the world's energy needs.

Other Uses of Grasses

It has been said that more structures are composed of bamboo than stone, brick, and wood combined! Although this may be an exaggeration, it certainly points out the importance of bamboo to billions of people living in Central and South America, Africa, Asia, and Oceania. Not only is bamboo used in construction but it can be a source of nutrition (bamboo shoots) as well as an occasional source of grain in time of famine (Gould and Shaw 1983). The nonfood uses of bamboo are endless, but here are a few examples: poles and posts for building construction, fence posts, bridges, boat masts, ladders, cages, flooring; shafts, spears, bows and arrows, fishing poles; handles for tools, whips, knives; furniture; window shades; woven articles such as mats, roofs, baskets; rope and cordage; water conduits and drainpipes; musical instruments; toys; cooking utensils; and a number of miscellaneous items such as chopsticks, pipe stems, sieves, writing paper, facial tissue, and cigarette papers (Gould and Shaw 1983; Chapman 1996). Bamboos also are used in religious ceremonies; as artwork; and as a source of medicine for asthma, coughs, fevers, and kidney problems. Fabric made from bamboo is becoming more and more popular and environmentally "acceptable."

Lemongrass (Cymbopogon) is used as a flavoring in cooking and, along with vetiver, is harvested for essential oils (National Research Council 1993). Other aromatic grasses (Hierochloa, Anthoxanthum), which contain coumarin, are used for perfumes, hair tonics, and flavoring vodka.

As mentioned previously, grasses are one of the largest families and, from a biodiversity standpoint, of great importance. Species composition, especially of grasses, in plant communities can be an indicator of past use, grazing capacity, wildlife habitat, and "ecological health." Some grasses have even been included on the endangered species list (Zizania texensis) (fig. 1.2d).

Harmful Grasses

Grasses are fairly benign, doing little harm to humans or animals compared to the benefits that they afford. That said, some fungi that use grasses as a host have caused serious problems throughout history; the alkaloids produced by the fungus Claviceps purpura L. has caused many deaths when ingested in significant quantities. "Ergot" is the term most commonly used for these endophytic fungal diseases. Ergot outbreaks caused hundred of thousands of deaths in the Middle Ages after contaminated grain (rye for the most part) was ingested (Lorenz 1979). "St. Anthony's fires" is the term often used for spontaneous hysteria caused by ergot poisoning. Some have even attributed the hallucinations and hysteria during the Salem witch episode in 1692 to ergot poisoning. Poisoning by ergot is very rare in modern times because of high agricultural grain inspection requirements. Surprisingly, the alkaloids produced by these fungi have shown potential for medicinal use (Chapman 1996).

Infected kodo millet (Paspalum scrobiculatum L.) and pearl millet (Pennisetum glaucum (L.) R. Br.) have caused intoxication and poisoning. The fungus Aspergillus tamaril Kita growing on these plants produces cyclopiazonic acid, which is toxic to humans (Krishnamachari and Bhat 1976). Maize (corn) contaminated with aflatoxins also has been reported to cause deaths in India (Bhat, Nagarajan, and Tulpule 1978). Consumption of any moldy grain should be considered a serious health hazard.

Allred (2005) lists the following harmful compounds produced by grasses that can cause poisoning: coumarin, cyanide, nitrates, and oxalates. He also lists other harmful effects of grasses as dermatitis, hay fever, asthma, and photosensitivity. Often forgotten is the harmful impact caused by mechanical injury. Generally the awns or stiff bristles that can penetrate soft tissues of the eyes, nose, throat, and underbelly cause problems among grazing animals (Allred 2005). One needs only a single experience of wandering into a "sticker" patch barefooted to marvel at the mechanical adaptations of Cenchrus for dispersal. Some think that the accumulation of secondary compounds, mutualism with fungi, and mechanical structures capable of injury are adaptations to combat herbivory (Vicari and Bazely 1993).

One should probably include negative economic impacts of grasses under the heading "Harmful Grasses." By definition, a weed is any plant growing where it is not wanted, so any plant could be considered a weed depending on the situation. Consider Bermudagrass for example: it is an important turf species for lawns, athletic fields, and road rights-of-way and a highly desirable forage species used for hay and domestic livestock grazing, but it also is a nuisance and difficult to control and eradicate from flower beds and St. Augustine lawns.

Many annual grasses and a few perennials would fit into the "weedy" category (fig. 1.2e, f). Cost of control of annual grasses such as crabgrass (Digitaria spp.), barnyardgrass (Echinochloa spp.), and goosegrass (Eleusine indica) is extremely high, and the chemicals used for control have negative impacts on the environment. The same applies to control of annual grasses in cultivated crops. Either through the cost of chemicals and application for herbicides or the fuel and labor costs in cultivation, "weedy" grasses negatively impact human food and fiber production and costs.

Grasses also play a role in the realm of "unintended consequences." In an effort to increase national security by reducing dependence on foreign petroleum, as well as reduce carbon emissions by using cleaner fuels, the addition of ethanol to gasoline has been on the increase over the last decade. Most if not all of us would agree this is a "good" thing. In the United States, ethanol has been primarily made from an annual cultivated grass—corn. To increase production of ethanol, farmers are planting more acres into corn, thus increasing the amount of nitrogen and phosphate fertilizer going into the environment. These chemicals accumulate in watersheds and eventually make their way to the Gulf of Mexico, where they create "dead zones" in the marine environment. Fish and shrimp harvests have been diminished—increasing prices for us all—and harvesters have to search farther from shore for longer periods of time to find their catch, increasing fuel consumption and carbon emissions, and further increasing commodity prices. Most of us would agree these are "bad" things.

Grasses impact our lives every day, in obvious and sometimes not so obvious ways. Grasses have been inseparable from human social structure since its beginnings. As go the grasses, so goes human society.

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Excerpted from Guide to Texas Grasses by Robert B. Shaw, Paul Montgomery. Copyright © 2012 Texas A&M University Press. Excerpted by permission of Texas A&M University Press.
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