Smooth Brome

Bromus inermis

Species distinguishing characteristics: 

  • Perennial grass often forming sod from long rhizomes
  • Flat, 3–10 mm wide, leaf blades with W-shaped constriction
  • Leaf sheaths closed, ligules turn back at the tips, and auricles lacking
  • Green to brownish purple, nodding, open flower clusters with whorled branches   
  • Spikelets elongated and cylindrical
  • Awns of lemma lacking or less than 2 mm long, and lemmas are round on back
  • Can invade native plant communities

Family Characteristics: 

  • Flowering stems have nodes and are hollow and round in cross section
  • Alternate leaves sheath the stem on their lower portion and form a hairy or membranous scale (ligule) inside the base of the leaf sheath
  • Flower clusters of numerous spikelets attach directly to the flowering stem (spike) or attach by small stalks, and are often branched (panicle)
  • A pair of bracts, called glumes (the outer/lower one being larger), enclose spikelets at the base
  • Each spikelet has one or more florets (dry, single seeded flowers) surrounded by 2 bracts (a lower lemma and a small, upper palea)
  • Lemmas and/or glumes may have needle-like, stiff hairs (awns)
  • Florets have 3 stamens (pollen organs) and 2 feathery stigmas (tip of a female organ for receiving pollen) but lack showy petals and sepals as they are wind pollinated
  • Fruit is a seed-like grain enclosed in the bracts (called chaff in cereal grains)
  • Well-known members of this family include cereal grains such as wheat (Triticum spp.), corn (Zea spp.), rice (Oryza spp.), and oats (Avena spp.)

Growth habitat: 

Perennial grass, 30–120 cm tall, that often forms dense colonies or sod from long, strong rhizomes.  Introduced as a pasture or forage grass from Eurasia in the 1880s.

Leaves and stems: 

Erect, unbranched stems.  Foliage is smooth to sparsely fuzzy-haired.  Flat, prominently veined leaf blades, 3–10 mm wide and 10–40 cm long, with rough margins and a distinct W-shaped constriction at the midpoint.  Leaf blades are grayish-blue on the upper surfaces, green on the underside and are somewhat limp in habit.  The waxy leaf sheaths fuse around the stem but split open near the ligules.  The ligules, 0.5–3 mm long, are minutely jagged or turn back at the tips.  Auricles, or small, clasping appendages on the collar of the leaf sheath, are usually lacking.

Flowers: 

Whitish-green to pale brown or purple-tinged, narrow, nodding (or drooping sideways) panicles, 7–20 cm long, at tips of stems.  Panicles have 1–4 branches that are whorled at each joint and often divided into wiry, secondary branchlets.  During bloom (when yellow pollen sacks protrude out of the florets), branches in the panicle are ascending or spreading; otherwise, they are erect and crowded.  Elongated spikelets, 1.5–3 cm long and less than 0.6 cm wide, are cylindrical but taper near the base and point at the tip.  Each spikelet has 4–13 flowers, a pair of papery, unequal sized glumes, and 5–10 longer, fertile lemmas that are arranged in 2 columns.  The smaller glume, 4–6 mm long, has 1 nerve and the larger glume, 6–10 mm long, has 3 nerves.  The lemmas, 8–12 m long, are round on the back (rather than keeled) and have several veins on the outer surface.  Lemmas usually lack awns or occasionally have straight awns that are less than 2 mm long.

Roots: 

Long, strong rhizomes that can grow up to 5 feet deep into the soil, and fibrous roots.  Rhizomes have a white core covered with a brown, net-like sheath.

Seeds: 

Tan to light brown seeds, about 0.8 cm long.

Habitat preferences: 

Moist to moderately dry open sites, forests, meadows, grasslands, stream banks, roadsides, ditches, hayfields, pastures, and other disturbed areas at low to subalpine elevations.  It is fairly drought resistant and can grow on rocky and sandy soils but is more abundant in fertile loam soils.

Interesting facts: 

Many species of leafhoppers (Cicadellidae spp.) and grasshoppers (Caelifera spp.) and a few species of moth (Lepidoptera spp.)larva feed on smooth brome.  Dense colonies of smooth brome provide cover and food (seeds and foliage) for small rodents.  Upland game birds, such as ring-necked pheasants (Phasianus colchicus), and some sparrows (Passeridae spp.) feed on the seeds of smooth brome.

Rabbits (Leporidae spp.), elk (Cervus elaphus), deer (Cervidae spp.), and livestock use smooth brome for forage.  Consuming smooth brome does not injure the mouthparts and gastrointestinal tract of ungulates because the spikelets lack the awns found in other species of brome (the name inermis means “smooth or lacking sharp awns”).  Smooth brome is widely used as forage for livestock in hayfields and pastures as a result of this quality and its high nutrient content.  However, its strongly rhizomatous nature make it a highly aggressive competitor that can spread into native plant communities.  Smooth brome is also commonly planted to prevent soil erosion after disturbance and for wildlife cover.  This enhances its ability to exclude growth of most other species, reducing species diversity, and ultimately shortening the season of forage availability.  The best method for slowing the spread of smooth brome is to refrain from introducing it into the environment.  Smooth brome can be controlled with the application of herbicide after frequently cutting the plant (at least 3 repetitions) once it reaches a height of 45 cm.

Biological Classification: