Bromus inermis (Smooth Brome)

Plant Info
Also known as:
Genus:Bromus
Family:Poaceae (Grass)
Life cycle:perennial
Origin:Europe
Status:
  • Invasive - ERADICATE!
Habitat:part shade, sun; disturbed soil; roadsides, woodlands, woodland edges, fence rows, fields, waste areas
Fruiting season:July - September
Plant height:20 to 50 inches
Wetland Indicator Status:GP: UPL MW: FACU NCNE: UPL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle

[photo of flowering panicle] Flowering head is an open panicle 4 to 8 inches long, at flowering time erect with the branches ascending to spreading, and 2 or more spikelets (flower clusters) per branch. Spikelets are stalked, oblong in outline, slightly flattened, 15 to 25+ mm (to 1+ inch) long, with 6 to 13 fertile florets. One or more sterile florets may be at the tip.

[close-up of spikelet] At the base of a spikelet is a pair of bracts (glumes), both hairless and blunt at the tip, the lower glume 6 to 9 mm long and 1-veined, the upper glume 7 to 11 mm long and 3-veined. Surrounding a floret is a pair of bracts (lemma and palea). Lemmas are lance-elliptic, 9 to 14 mm long, 5 to 7-veined, obscurely notched at the tip forming 2 teeth, awnless or with a straight awn up to 2.5 mm long arising between the teeth, hairless or the lemma body minutely hairy near the base. The palea is somewhat shorter than the lemma and hairless to minutely hairy. Sterile florets are like the fertile but underdeveloped.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaf blades are spreading to ascending, flat, 4 to 14 inches long, 5 to 15 mm (to ½+ inch) wide, usually hairless, occasionally with a few hairs near the base. About midway up the blade is often a W-shaped wrinkle or constriction.

[photo of sheath, ligule and node] Sheath edges are fused for most of their length (a closed sheath), usually hairless, sometimes minutely hairy or with just a few long hairs near the tip. The ligule (membrane where the leaf joins the sheath) is membranous, up to 3 mm long, jagged along the top edge and lacks a fringe of hairs. Nodes are usually hairless. Stems are erect to ascending, usually hairless, sometimes minutely hairy or hairy just at the nodes, single or a few from the base, and forming colonies from creeping rhizomes. 

Fruit: Fruit type: seed_without_plume

[photo of maturing panicle] The flowering head becomes more contracted with maturity, the branches becoming more erect to ascending, later often nodding to one side with the spikelets drooping.

[photo of mature florets and grain] Florets mature to bronzy brown or purplish, each dropping off individually leaving the glumes persisting on the stalk. Grains are somewhat flattened, 6 to 7.5 mm long, and have a bundle of white hairs at the tip.

Notes:

Bromes are cool season grasses (optimal growth below 75°), usually clump-forming, have closed sheaths, panicles that are often drooping or nodding to one side, multi-flowered spikelets, unequal glumes, and lemmas that are typically awned, hairy and usually notched at the tip forming 2 teeth with the awn arising between the teeth. The longer leaves also frequently twist from near the base so the underside and upperside are flipped. Most Bromes found in Minnesota have sheaths and nodes that are hairy to various degrees and are mostly distinguished by the number of veins on the glumes, length of the lemma awns, and sometimes leaf characteristics.

A European introduction, Smooth Brome has been widely used in roadside plantings for erosion control and agriculturally for forage, but has spread beyond that to natural areas where it can be a bad pest, crowding out native species and reducing diversity. Besides being the only rhizomatous Brome in Minnesota, it is distinguished by being mostly hairless, the 1-veined lower glume, 3-veined upper glume, and lemmas that may be minutely hairy only near the base and are awnless or short awned. While some references state it can reach heights of 4+ feet, 2 to 3 feet is more common, particularly in areas subject to mowing. Like Reed Canary Grass, Smooth Brome is pretty ubiquitous and it's discouraging to see it so widely planted.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos by Peter M. Dziuk taken at various locations in Minnesota.

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