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Grasses

Grasses can be highly successful weeds or invasive species. This is related, in part, to the fact that the seeds of most grasses are wind-dispersed and can be moved long distances. Grasses also often have extensive vegetative reproduction, through structures such as tillers, rhizomes, and stolons (Fig. 8). All of these are primary modifications of the main part of the grass plant, the culm (Gibson 2009). Tillers are aboveground branches that develop at the base of the culm. All grasses produce tillers, but they are particularly associated with a bunch-grass habit. Rhizomes, by contrast, are belowground lateral stems that appear like roots. Stolons, sometimes called runners, are aboveground lateral stems that spread out horizontally from the culm and can start new plants if separated from the culm.

Fig. 8. The basic structure of a grass is based on a culm. Culms may spread aboveground via stolons or belowground via rhizomes. Vegetative structures such as auricles or ligules can be important identifying characteristics for some grass species. Reprinted from Hatch, Schuster, and Drawe (1999), used with permission from Texas A&M University Press.

The rate at which tillers, rhizomes, and stolons grow is related to the amount of energy in the culm. Some grass species are considered to have a phalanx life history, which means that they usually have short tillers or rhizomes and move outward in a mass (like the formations used by Greek and Roman armies, described using the same term) (Lovett Doust and Lovett Doust 1982). Phalanx plants tend to develop in low-nutrient environments with lots of light. In contrast, guerilla plants—as the name implies—stealthily spread into areas where there is limited space available, often via long stolons. Guerilla plants tend to grow in moist areas that have high nutrients with little available light. These plants may also occupy disturbed areas that are more nutrient-rich than the surroundings.

Because of their abundant, wind-dispersed seeds and their vegetative growth, grasses tend to be difficult to control. It is important to prevent these plants from setting seed, which is most easily accomplished by repeated removal of flowering stems. Mowing slows the rate of grass spread but is unlikely to control it in most cases. In some habitats, professionally monitored controlled burns are used to maintain certain plant communities. However, fire tends only to retard the growth of invasive grasses, rather than completely remove them. An additional effective control measure is solarization, whereby invasive grasses are covered with plastic sheeting to raise the temperature and kill off the plants. Herbicides that incorporate glyphosate can be applied as nonspecific controls, but there are also grass-specific herbicides, such as sethoxydim.

The literature pertaining to grasses has developed somewhat independently of other plant species, mostly because researchers studying the grasses were often rangeland ecologists or pasture scientists. Consequently, terminology has been developed for structures in grasses that is largely distinct from that of other plants. The presence of jointed nodes distinguishes grasses from other grasslike plants. The flowering stems of true grasses are hollow at maturity. There are many terms specific to the identification of grass species, in both the vegetative and the reproductive structures (Figs. 8 and 9).

Fig. 9. A grass inflorescence has a number of specialized structures. The floral parts may differ in key identifying features. The spikelets consist of glumes, a palea, and a lemma. The awns, used by many grasses to move their seeds, are also key characteristics. The grass flower has female parts in the pistil, which consists of an ovary and a stigma, and the male parts in the stamen, which consists of a filament and the anthers. Drawing by Susan Kashanski (2002), used with permission from the US Fish and Wildlife Service, National Conservation Training Center, Shepherdstown, West Virginia.

Cool- and Warm-Season Grasses and Likely Responses to Global Warming

Grasses, which evolved about 80 million years ago, comprise a bewildering array of species. In the course of evolution, grasses initially used one type of photosynthesis (as did most other plants), termed C3 photosynthesis. This type is more widespread and refers to the way plants obtain carbon dioxide (CO2) during photosynthesis. All species have the more primitive C3 pathway, which involves a three-carbon molecule; hence its name. More recently, about 31–34 million years ago, an additional C4 pathway, which involves a four-carbon molecule, evolved in species that occur in the dry and wet tropics. C4 plants are typically associated with habitats that have high temperatures and/or frequent droughts. In contrast, C3 plants tend to grow in cooler climates, often where frost is common. Consequently, grasses with these two photosynthetic pathways are often termed cool- (C3) and warm-season grasses (C4.) In Ohio, there are grasses that use both C3 and C4 photosynthetic pathways (Teeri and Stowe 1976). It is widely accepted among scientists that with increasing global temperatures, C4 species will replace C3 species (see, for example, Edwards and Still 2008). Because cool-season grasses are often critical forage species for cattle, this could have important consequences for economics and food production, as well as for ecosystems.

Poaceae

Arthraxon hispidus

small carpetgrass ∙ small carpgrass ∙ hairy jointgrass ∙ jointhead grass ∙ jointhead arthraxon

Origin: Native to Africa, southern and eastern Asia, and Oceania. This species was first recorded in the United States in the 1870s. Introduction was most likely accidental. It now has a patchy distribution throughout the eastern United States, primarily in the mid-Atlantic region.

Description: A low-growing, warm-season annual grass with broad leaves. Arthraxon hispidus resembles the native Dicanthelium clandestinum (deertongue grass), but D. clandestinum has a pyramid-shaped inflorescence and longer and more pointed leaves, its leaf margins lack hairs, and its stems do not root at the nodes. It is also similar to the nonnative Microstegium vimineum (Japanese stiltgrass), but the leaves of M. vimineum lack a heartshaped base.

Habitat: Forest margins, floodplain forest, swamps, lake or pond shorelines, river- and streambanks, wet meadows, pastures, fields, ditches, and roadsides. Prefers full sun and moist to wet soils.

Height: Flowering stems typically 30–50 cm (12–20 in.), occasionally to 1 m (40 in.).

Foliage: Leaves are oval or lance-shaped, 2–7 cm (¾–3 in.) long and 5–20 mm (¼–1 in.) wide, each with a pointed tip and a heartshaped base that encircles the stem. The leaf blade is hairless, but the margins of the leaves have conspicuous hairs. The leaf has a membranous ligule, 0.5–3.5 mm long, with fine hairs along the margin.

Flowers: Flowers are pale green or purple, in spikes 2–8 cm (¾–3 in.) long, held singly at the ends of stems or clustered in groups of 10 or more diverging from a common point of attachment. Each spikelet is 3–5 mm (⅛–¼ in.) long, containing a single floret with two anthers and an awn that is 6–11 mm (¼–½ in.) long. September–October.

Fruit: –⅛ in.) long and 0.4–0.6 mm wide. October–November.

Stems: Stems are slender and hairless except at the nodes. Stems trail along the ground near the base then grow upright.

Root system: Slender, fibrous roots form a shallow root system. Secondary rooting can occur at the nodes where they contact the soil.

Reproduction: By seed, which is dispersed by flooding, animals, machinery, or movement of soil.

Impact: Forms dense monocultures that displace native plant communities, particularly in ephemeral habitats along the margins of water bodies.

Control: Mechanical treatments are most effective when plants are just starting to flower. Pull or mow before seeds are produced. Since this species often grows in wet environments, only aquatic formulations of glyphosate and sethoxydim should be used for control. If this grass is growing in or near a wetland habitat, chemical applications should be made only by a licensed aquatic herbicide applicator.

Stand of Arthraxon hispidus. Image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Leaves and stems of Arthraxon hispidus. Image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Arthraxon hispidus inflorescence. Image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Arthraxon hispidus infructescence. Image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Fruits of Arthraxon hispidus. Image by Steve Hurst, hosted by the USDA-NRCS PLANTS Database.

Roots and dried stems of Arthraxon hispidus. Image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Poaceae

Bromus inermis

smooth brome ∙ bromegrass ∙ awnless brome ∙ Hungarian brome ∙ Austrian brome ∙ Russian brome

OIPC Invasive

Origin: Native to Europe and eastern Asia. This species, which was intentionally introduced to North America in the late 1800s, has been widely planted as forage for livestock and erosion control along waterways.

Description: A cool-season, perennial rhizomatous grass. This species starts growth in early spring and forms a dense sod.

Habitat: Sunny areas along roadsides, ditches, fields, pastures, and prairies. Can withstand drought, extreme temperature, and periodic flooding.

Height: Stems typically 50–100 cm (20–40 in.).

Foliage: in.). There is often an M-shaped constriction between the center and the tip of the leaf that is diagnostic of all bromes but is especially prominent in Bromus inermis.

Flowers: Inflorescence is a drooping panicle, 10–20 cm (4–8 in.) long, with 4–10 branching spikelets that are 15–30 mm (⅝–1¼ in.) long and each contain 7–11 florets. Florets have two or three large yellow anthers and white stigmas. May–July.

Fruit: Inflorescence develops a characteristic purple-brown color when mature. Bracts golden or tan, 8–12 mm (¼–½ in.), usually awnless and smooth. Caryopses are brown, flat, 7–9 mm (¼–⅜ in.) long. June–August.

Stems: Smooth or finely haired at nodes.

Root system: Rhizomes with dark brown scales.

Reproduction: Aggressively spreads through tillers and rhizomes. Seeds are dispersed by wind, water, birds, and mammals. Seeds in the soil seed bank remain viable for up to 10 years.

Impact: This species is highly competitive because it starts growth early in the spring and forms a dense sod. This is of particular concern in prairie habitats, where it outcompetes later growing, warm-season prairie species.

Control: Perennial, cool-season grasses like Bromus inermis can be controlled by manual, mechanical, and chemical means. Annual spring burning, intensive early spring grazing, or intensive early spring mowing can be used to reduce B. inermis cover in prairies dominated by warm-season grasses. Grass-specific herbicides such as sethoxydim can be applied in spring or autumn when native grasses are dormant.

Native Alternatives

Andropogon gerardii (big bluestem)

Calamagrostis canadensis (Canada bluejoint)

Calamovilfa longifolia (prairie sandreed)

Eragrostis spectabilis (purple love grass)

Schizachyrium scoparium (little bluestem)

Sporobolus heterolepis (prairie dropseed)

Tridens flavus (purpletop tridens)

Sorghastrum nutans (Indiangrass)

Stand of Bromus inermis. Image by Robert Vidéki, Doronicum Kft., Bugwood.org.

Leaf sheath and stem of Bromus inermis. Image by John Cardina, The Ohio State University, Bugwood.org.

Bromus inermis ssp. inermis fruit. Image by D. Walters and C. Southwick, Table Grape Weed Disseminule ID, USDA APHIS PPQ, Bugwood.org.

Bromus inermis inflorescence. Image by Patrick J. Alexander, hosted by the USDA-NRCS PLANTS Database.

Bromus inermis infructescences. Image by Matt Lavin, used under a CC BY-SA 2.0 license.

M-shaped constriction on the leaf of Bromus inermis. Image courtesy of Fontenelle Nature Association.

Poaceae

Cynodon dactylon

Bermudagrass ∙ Bahama grass ∙ wire grass ∙ devil grass ∙dog’s tooth grass ∙ couch grass ∙ quick grass ∙ star grass ∙ scutch grass ∙ vine grass

Origin: This species likely originated in eastern Africa but now occurs in tropical and subtropical regions worldwide. It is frequently cited as having been introduced to North America as a pasture species in the mid-1800s, but some accounts suggest that it was already established by 1807.

Description: A low-growing, warm-season perennial grass. Spreading stolons and rhizomes form a dense sod.

Habitat: Open woods, disturbed grasslands, riparian areas, plantations, agricultural fields, orchards, pastures, gardens, and roadsides. It grows in almost all soil types. Prefers a warm climate, moderate moisture, and full sun.

Height: 5–45 cm (2–18 in.).

Foliage: in.), with a conspicuous fringe of white hairs.

Flowers: –⅛ in.) long, containing a single floret with three anthers, awnless. July–October.

Fruit: Brown, ellipsoid caryopses, 1–2 mm long and 0.5 mm wide, slightly compressed. July–October.

Stems: Branching stems creep along the ground and root at the nodes where they contact the soil. Stems are round in cross section or slightly flattened, swollen at the nodes, often slightly purple.

Root system: Deep roots make this species extremely drought tolerant. Mature roots are yellow or brown, while young roots are white. Produces rhizomes that contribute to lateral spread.

Reproduction: By abundant seeds, dispersed by water, soil movement, machinery, as a contaminant of agricultural seed, and in livestock feed and bedding. Seeds remain viable in the soil seed bank for three to four years. Vegetative spread also occurs via creeping stolons and rhizomes.

Impact: Many cultivars—including ‘Tifgreen,’ ‘Riviera,’ and ‘Wrangler’—have been developed, and this species continues to be planted for erosion control and as a turf grass. Nevertheless, it is considered a noxious weed in several states and is a major weed of many crops worldwide. This species can escape cultivation and outcompete native vegetation in disturbed habitats. Due to its production of allelopathic compounds, it is highly aggressive. Cynodon dactylon also produces highly allergenic pollen, making it problematic for human health.

Control: Small patches should be dug out, taking care to remove all rhizomes and stolons. If using a solarization method, mow, irrigate, and cover with a black plastic sheet for six to eight weeks in summer. Grass-specific herbicides such as sethoxydim can be used in early spring, with follow-up applications through the growing season. Nonselective herbicides such as paraquat and glyphosate are most effective in the spring or autumn, when rhizomes are growing.

Native Alternatives

Agrostis hyemalis (ticklegrass)

Festuca rubra (red fescue)

Tridens flavus (purpletop tridens)

Cynodon dactylon plant. Image by Steve Dewey, Utah State University, Bugwood.org.

Cynodon dactylon leaves and stem. Image by Doug Goldman, hosted by the USDA-NRCS PLANTS Database.

Cynodon dactylon florets. Image by Doug Goldman, hosted by the USDA-NRCS PLANTS Database.

Inflorescence of Cynodon dactylon. Image by Doug Goldman, hosted by the USDA-NRCS PLANTS Database.

Cynodon dactylon fruits. Image by Steve Hurst, hosted by the USDA-NRCS PLANTS Database.

Scrambling growth habit of Cynodon dactylon. Image by Doug Goldman, hosted by the USDANRCS PLANTS Database.

Poaceae

Dactylis glomerata

orchardgrass ∙ cat grass ∙ cocksfoot grass ∙ cockspur

Origin: Native to Europe, Asia, and northern Africa. This species was introduced to the eastern United States in 1760 as a pasture species and is still widely planted for forage.

Description: A cool-season perennial bunchgrass that grows in dense tussocks with upright flowering stems.

Habitat: Meadows, orchards, pasture, grassland, open woodland, forest, riparian areas, freshwater wetlands, and roadsides. Adapted to welldrained, fertile soils with moderate moisture and temperature. It is shade tolerant and tends to grow in areas with a history of disturbance.

Height: Flowering stems 30–150 cm (12–60 in.).

Foliage: Leaves are folded in the bud. Leaf blades are 20–50 cm (8–20 in.) long and 3–11 mm (⅛–½ in.) wide, strongly keeled with a prominent midvein on the underside, hairless or covered in tiny prickles giving them a rough texture. Leaf margins are minutely toothed. The ligule is a membrane 5–10 mm (¼–½ in.) long, occasionally fringed with short hairs. The leaf sheath is smooth, keeled, with margins fused together to form a closed tube except toward the top.

Flowers: in.). May– September.

Fruit: in.) wide. June–October.

Stems: Hairless stems, flattened at the base.

Root system: An extensive fibrous root system that produces a dense sod. This species produces very short rhizomes or no rhizomes.

Reproduction: By abundant seed, dispersed by wind, animals, and human activity. It also spreads vegetatively through tillers.

Impact: This species is widespread and is a valuable pasture grass in many places. Its negative impact is relatively small, although it is considered weedy or invasive in parts of the United States and in other countries around the world. Dactylis glomerata has been found to suppress native plants in rare habitat types such as savannas, so it is worth monitoring to ensure that it does not spread into high-risk areas.

Control: Plants can be dug out, taking care to remove the root crown to prevent regrowth. So that seed does not set, large stands should be mowed before flowering. Repeated close mowing can eliminate this species entirely.

Dactylis glomerata plant. Image by Ohio State Weed Lab, The Ohio State University, Bugwood.org.

Leaf sheath and ligule on Dactylis glomerata. Image by Rob Routledge, Sault College, Bugwood.org.

Dactylis glomerata stems. Image by Ohio State Weed Lab, The Ohio State University, Bugwood.org.

Dactylis glomerata florets. Image by Doug Goldman, hosted by the USDA-NRCS PLANTS Database.

Dactylis glomerata inflorescence. Image by Catherine Herms, The Ohio State University, Bugwood.org.

Dactylis glomerata fruits. Image by Steve Hurst, hosted by the USDA-NRCS PLANTS Database.

Poaceae

Echinochloa crus-galli

barnyardgrass ∙ barn grass ∙ barnyard millet ∙ Japanese millet ∙ wild millet ∙ watergrass ∙ summergrass ∙ cockspur ∙ cocksfoot panicum ∙ chicken panic grass ∙ billion dollar grass ∙ German grass

Origin: The native range of this species is somewhat obscure. This species is thought to have originated in tropical Asia and warmer regions of Europe but is now distributed throughout tropical and temperate regions worldwide. It was likely introduced to North America from Europe as a contaminant in crop seed in the early 1800s. Because it reduces crop yields significantly, Echinochloa crus-galli is considered one of the world’s worst weeds.

Description: A tall, warm-season annual grass with thick stems that branch at the base. Stems can be solitary or grow in small