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Grasses of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

Smooth Brome

Common Name
Smooth Brome (Hungarian Bromegrass)

 

Scientific Name
Bromus inermis Leyss.

 

Plant Family
Poaceae (Grasses)

Garden Location
Woodland & Upland

 

Prime Season
May to June flowering

 

Grass structure and definitions - PDF from Oregon State University

Ligule Types, Shapes & Margins (pdf)

 

Smooth Brome is a perennial introduced grass with stems (culms) that are single or a few together, growing 1.5 to 4 feet high. Nodes number 3 to 5. Stems and nodes are usually without hair.

Leaves: Leaves are both basal and stem, flat, to 15mm wide (5/8 inch), 4 to 14 inches long, numerous and frequently marked by wrinkle like a "W" a short distance below the tip.

Sheath throats and collars are usually without hair; The ligule is often brownish at the base, truncate, and the collar is hairless and light or yellowish green. Auricles are sometimes present. Sheaths are split.

The inflorescence is a panicle, 4 to 8 inches long, of open shape and erect with ascending branches. It colors to purplish brown when mature.

Flowers & spikelets: Spikelets are 20 to 40 mm long, somewhat elliptic to lanceolate in shape with 8 to 10 florets. Spikelets may be purplish prior to maturity but are purplish-brown at maturity. Both lower and upper glumes are veined (1 vein usually on the lower and 3 on the upper), the upper glume longer (7 to 10 mm), both without hair. Lemmas are 9 to 13 mm long, also mostly elliptic to lanceolate in shape, rounded over the midvein, smooth, but margins may occassionally have sparse hair. Florets have 2 anthers and awns that are usually absent, but if present are straight and to 3 mm long.

CAUTION - Invasive: Smooth Brome is normally used as a forage plant where it can be controlled. It was formerly recommended for wildlife plantings but no longer as it is an aggressive grower and can become invasive. In Minnesota it is one of three grasses listed as an invasive non-native terrestrial plant.

 

Habitat: Smooth Brome is a leafy, sod-forming, perennial, cool season grass that spreads by rhizomes. It grows in sun and partial shade, tolerant of various soils and mositure conditions - a trait of many invasive plants.

Names:The genus Bromus, is derived from the Greek bromos, referring to oats, as the flowering heads of this genus resemble oats somewhat. The species, inermis, means 'unarmed' or 'without prickles', in this species referring to the usual absence of awns on the florets. The author name for the plant classification, ‘Leyss.’ refers to Friedrich Wilhelm von Leysser (1731-1815), German botanist, author of Flora Halensis of 1761. The genus Leyssera is named after him.

Comparisons: The rhizomatous root system distinguishes this grass from the other two in the Garden. In North America Smooth Brome is similar to two other introduced species. 1) B. riparius, Meadow Bromegrass, but that species is shorter (only 12 to 30 inches) and has awns. 2) It is also similar to B. pumpellianus, the Arctic Brome, but that species usually have hair on the nodes, sheaths and glumes, and has long awns - to 7.5 mm. Neither of those species are found in Minnesota. There are three species of Bromus in the Garden. See bottom of page for an ID key.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Smooth Brome drawing

Above and below: Flower panicles with their ascending branches. Photos at various stages of development, all ©Phoebe Waugh. Drawing above by Ferdinand Vietz.

Smooth Brome Smooth Brome in flower

Below: 1st photo - The panicle beginning to mature. 2nd photo - Maturing spikelets.

Smooth brome seedhead Smooth Brome panicle

Below: The leaf sheath, collar and ligule. The ligule (most visible in the 2nd photo) is often brownish at the base, obtuse, and the collar is hairless and light or yellowish green.

Smooth Brome Ligule Smooth Brome Ligule

Below: Details of the florets, glumes and lemmas. Photos all ©Anna Gardner, University of Iowa.

florets lemmas

BELOW: A comparison of the three species of Bromis at Eloise Butler.

Species B. inermis B. latiglumis B. pubescens
Smooth Brome Earlyleaf Brome Hairy Woodland Brome
Rhizomes present Yes No No
Stems (all are erect)
Height 1.5 to 4 feet 3 to 5 feet 2 to 4 feet
# of stem nodes 3-5 9-20 5-7
Stems hairy? usually not usually not usually
Leaf sheaths hairy? usually not can be, throats and collars densely hairy usually, backward bent
Ligules to 3mm. smooth 0.8 to 1.4mm hairy 0.5 to 2mm smooth
Leaf Blades
Length 4 - 14", flat 8 - 12", flat 5 - 13", flat
Width to 15mm (5/8") to 15mm (5/8") to 15mm (5/8")
Hair on blades usually not usually not can be with or without
Special feature 2 prominent flanges on collar
Panicles 10 -20 cm long (4 to 8") 10 - 22 cm long 10 - 25 cm long
open open open
erect nodding usually nodding
Panicle branches ascending or spreading ascending or spreading spreading, sometimes ascending, usually drooping
Spikelets 20-40 mm long, sometimes purplish, with 8-10 florets 15-30mm long with 4-9 florets 15-30mm long with 5-10 florets.
Glumes with or without hair without either way usually soft fine hair
Lemmas usually without hair longhair on margins margins usually hairy
Awns present absent or to 3mm 3 - 4.5mm, straight 4-7mm, straight.

Notes:

Smooth Brome was introduced into California in 1884 from Hungary and is now found in all of North America north of Mexico except the states of Florida and Georgia. In Minnesota it is present throughout the state except for a few widely scattered counties. There are 52 species of Bromus in the United States, 28 native and 24 introduced. Eight of those species are in Minnesota - 4 native and 4 introduced. Worldwide the estimate is 100-400 species.

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

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