Bromus japonicus
(Japanese brome)

Preferred Scientific Name

• Bromus japonicus Houtt.

Preferred Common Name

• Japanese brome

Other Scientific Names

• Bromus abolinii Drobow
• Bromus anatolicus Boiss. & Heldr.,
• Bromus arvensis var. japonicus (Thunb.) Fiori
• Bromus barobalianus G.Singh
• Bromus cyrii Trin.
• Bromus gedrosianus Pénzes
• Bromus hirtus Licht.
• Bromus patulus Mert. & W.D.J.Koch
• Bromus pendulus Schur
• Bromus phrygius Boiss.
• Bromus pseudojaponicus H.Scholz
• Bromus regnii H.Scholz
• Bromus subsquarrosus Borbás
• Bromus ugamicus Drobow
• Bromus villiferus Steud.
• Forasaccus patulus (Mert. & W.D.J.Koch) Bubani
• Serrafalcus japonicus (Thunb.) Wilmott
• Serrafalcus patulus (Mert. & W.D.J.Koch) Parl.

International Common Names

• English: Japanese bromegrass; Japanese chess; Thunberg's brome
• French: Brome du Japon; brome japonais
• Chinese: que mai

Local Common Names

• Finland: Japaninkattara
• Germany: Japanische Trespe; Ueberhaengende Trespe
• Japan: suzumenochahiki
• Netherlands: japanse dravik
• Sweden: kvarnlosta

EPPO code

• BROJA (Bromus japonicus)

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Cyperales
•                         Family: Poaceae
•                             Genus: Bromus
•                                 Species: Bromus japonicus

Bromus L. is a taxonomically complex genus that includes 169 annual and perennial grass species with wide geographical distribution in temperate regions (Saarela, 2008; The Plant List, 2013).

Bromus japonicus Thunb. is an accepted name,and the species has two subspecies (B. japonicus subsp. anatolicus and B. japonicus subsp. japonicus and many varieties (The Plant List, 2013: USDA-ARS, 2016).

Three annual diploid species B. japonicus Thunb, B. squarrosus L. and B. arvensis are morphologically and genetically very similar. Oja et al. (2003) showed that B. japonicus and B. squarrosus are extreme selfers, whilst B. arvensis is an outcrosser with random mating. The researchers of the above study provided some isozyme evidence to support placement of B. japonicus under the name B. squarrosus. However a later study of Oja and Paal (2006) used cluster, PCA, classificatory and canonical discriminant analysis supporting the recognition of the three taxonomic units, but not recognizing any interspecific taxa within B. japonicus. The PLANTS Database (USDA-NRCS, 2016) treats B. japonicus as a synonym of B. arvensis, whereas on The Plant List (2013) they are two separate species.

The description of B. japonicus given by the Flora of China Editorial Committee (2016) states:

Annual. Culms erect, 40–90 cm tall. Leaf sheaths pubescent; leaf blades 12–30 cm × 4–8 mm, both surfaces pubescent; ligule 1–2.5 mm. Panicle effuse, 20–30 × 5–10 cm, nodding; branches 2–8, 5–10 cm, slender, each bearing 1–4 spikelets. Spikelets lanceolate-oblong, 12–20 × ca. 5 mm, yellowish green, florets 7–11, closely overlapping; rachilla internodes shortly clavate, ca. 2 mm; glumes subequal, keel scabrid, margins membranous, lower glume 5–7 mm, 3–5-veined, upper glume 5–7.5 mm, 7–9-veined; lemmas elliptic, 8–10 × ca. 2 mm in side view, herbaceous, 9-veined, usually glabrous, margins membranous with conspicuous angle at maturity, scabrid, apex obtuse, minutely 2-toothed, awned from 1–2 mm below apex; awn 5–10 mm, longer on upper lemmas than lower lemmas, base slightly flattened, conspicuously recurved at maturity; palea shorter than lemma, ca. 1 mm wide, keels stiffly ciliate. Anthers ca. 1 mm. Caryopsis 7–8 mm. Fl. and fr. May–Jul. 2n = 14.

B. japonicus has relatively greater root development than B. tectorum (Hulbert 1955).

B. japonicus was introduced to North America from Eurasia (Gilmartin et al., 1986)as a forage species. The time of introduction into the Northern Great Plains is unclear, although the related B. tectorum appears to have spread into Montana along railway lines (Haferkamp and Heitschmidt, 1999).

In Canada, B. japonicus was recorded in Ontario in 1912, with additional scattered records until 1948, after which it spread more rapidly (Dore and McNeill, 1980). It was uncommon in western Canada in the 1960s, but by 1980 was “abundant in the dry lands of southern Alberta and adjacent British Columbia” (Dore and McNeill, 1980). It is now present in most provinces and is reported to be expanding its range (Darbyshire, 2010; Canadian Food Inspection Agency, 2015).

Soil drainage

• free
• impeded
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral
• very alkaline

Soil texture

• heavy
• light
• medium

Special soil tolerances

• saline
• shallow

Natural Dispersal

B. japonicus has similar invasion patterns in disturbed vegetation types to those of B. tectorum (Gasch et al., 2013); i.e. the seeds are too heavy to be moved far by wind but are distributed by animals and livestock, or by soil cultivation actrivities.

Accidental Introduction

B. japonicus seeds can travel long distances along railway tracks (Wrzesien, 2011). In Canada it occurs as a weed in crops, and is known to contaminate seed and grain, particularly grass seed and wheat grain (Canadian Food Inspection Agency, 2015).

B. japonicus is an aggressive and persistent invasive species. It is reasonably palatable to livestock when young but rapidly becomes indigestible as it matures (US Forest Service, 2016). It negatively impacts perennial grass biodiversity, and can alter seasonal patterns of rangeland forage production and quality and livestock performance (Haferkamp et al., 2001; Harmoney, 2007, Gasch et al., 2013). In the North China Plain B. japonicus is one of the most abundant species of grass weeds found in the winter wheat production system (Menegat et al., 2012). B. japonicus is competitive with wheat and may reduce its yield by 30% (Qi et al., 2015). It is a weed of both cropland and rangelands in Canada, and is often an indicator of poor range condition. In Saskatchewan, B. japonicus is problematic in overgrazed pastures and a concern in forage and reclaimed sites (Canadian Food Inspection Agency, 2015).

B. japonicus has been recorded as a host plant for maize dwarf mosaic virus (Lee, 1964). It is also susceptible to wheat yellow streak-mosaic virus (McKinney and Fellows, 1951).

Impact on Habitats

Invasive grasses such as B. japonicus may increase soil infiltration in invaded plots due to a high concentration of fine brome roots in the top few centimetres in the soil, creating a persisting dense network of pores. (Gasch et al., 2013)observed that brome-dominated soils have increased levels of total N and mineral N, with the amount of organic C at similar levels to that in native soils, despite higher litter accumulation in invaded soils. Although the exotic annual bromes add to belowground C levels, the decomposing of brome root biomass results in net C loss through respiration. Invasive bromes extract shallow soil moisture earlier in the growing season than most native perennial species, contributing to much drier conditions in the top layer of the invaded soil profile. Bromes slow down decomposition of aboveground litter (Ogle et al., 2003; Kulmatiski et al., 2006, Gasch et al., 2013).

Impact on Biodiversity

B. japonicus has a negative impact on biodiversity and succession of grassland communities. Invasive grasses may double the herbaceous biomass while reducing the plant species functional group cover to extremely low levels long-term. Increase of species richness of invaded plots with increasing area is at a much lower rate than in native plots.

B. japonicus is one of the annual invasive grasses posing a threat to Silene spaldingii, a rare endemic species found in bunchgrass grasslands and sagebrush-steppe, and occasionally in open pine communities, in eastern Washington, northeastern Oregon, west-central Idaho, western Montana, and barely extending into British Columbia, Canada (US Fish and Wildlife Service, 2007). Along with other species such as Bromus tectorum and B. secalinus, B. japonicus degrades the habitat where S. spaldingii is found.

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Tolerant of shade
• Has propagules that can remain viable for more than one year

• Ecosystem change/ habitat alteration
• Negatively impacts agriculture
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Herbivory/grazing/browsing

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult/costly to control

B. japonicus can be used as an inexpensive alternative to seed cakes, bran and grains for preparing wet baits for locusts (Verescagin, 1942). It provides forage for grazing animals, but as it matures more quickly than perennial grasses its presence alters the timing of maximal forage production and quality, necessitating a change in livestock management compared with native North American rangelands (Haferkamp and Heitschmidt, 1999).

Rodents such as jumping mice (Zapus hudsonius luteus) feed on the achenes or seeds of Japanese brome (Wright and Frey, 2014).