Bromus diandrus

Bromus diandrus is a species of grass known by the common names great brome and "ripgut brome".

Bromus diandrus
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Poaceae
Subfamily: Pooideae
Genus: Bromus
Species:
B. diandrus
Binomial name
Bromus diandrus
Roth
Synonyms

Anisantha diandra (Roth) Tutin ex Tzvelev

Description

This is a brome grass which is native to the Mediterranean but has been introduced to much of the rest of the world. It does best in areas with a Mediterranean climate, such as California and parts of southern Australia, but it is quite tolerant of many climates. Ripgut brome is a winter annual which grows throughout winter and spring and matures in the summer. The adult plant is one to three feet in height with hairy, rough leaves about a centimeter wide. The membranous ligule is prominent, white in color with spiky hairs. The wide panicle nods like that of an oat plant, and it bears a large, splayed spikelet with a very long awn which can exceed five centimeters in length. The seeds easily break out of the spikelet. They are very sharp and very rough due to tiny barb-like hairs that face backwards, allowing the seed to catch and lodge like a fish hook. This characteristic makes the seeds a danger to animals, which can easily get a seed lodged in a paw or eye. Motion can cause the seed to work itself deeply into flesh. This is one of several grass species known to pet owners as "foxtails", a backyard hazard for outdoor cats and dogs.

Invasive species

Ripgut brome can substantially reduce yields when it invades wheat fields. It has naturalized in some areas and is considered a troublesome noxious weed in others. Bromus diandrus is an invasive species in California native habitats.

This brome grass is a troublesome weed in cereal crops and natural pasture lands. The life cycle of B. diandrus helps it to grow in wheat fields in which it can grow for most of the season without being noticed. Once the grass starts flowering, the open panicle seed head shows the infestation[1]. The damage to wheat crop is through both strong competition, lowering yield, and seed contamination, lowering quality.

Bromus diandrus infestation in wheat, NZ

Ripgut brome is also troublesome in rangeland if it establishes in high numbers. The grass is of low nutritional value to livestock. Brome seeds can also mix with sheep wool and lower its value. Moreover, sharp awns of ripe seeds can penetrate sheep’s skin into the flesh causing pain and lowering carcass value. If ingested, the strong awns can cause injury to sheep’s mouth and even intestine,[2] hence the name, ripgut.

Similar species

Bromus rigidus, known as rigid brome, is very similar in morphology to ripgut brome but differs from the latter in its panicle structure and the callus-scar of its caryopsis. The two species have some differences in their germination behaviour as well.[3] Bromus sterilis or sterile brome, is similar in most morphological features, it is a slightly smaller plant which can be an annual or a biennial plant.[2] Bromus hordeaceus, known as soft brome, is similar in early growth stages with smaller leaf blades. The seed head is an erect panicle, smaller than B. diandrus with much smaller seeds and much shorter awns.[1][2]

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References
  1. Dastgheib F. & Poole N. 2010. Seed biology of brome grass weeds (Bromus diandrus and B. hordeaceus) and effects of land management. New Zealand Plant Protection 63: 78-83
  2. Edgar E. & Connor H.E. 2000. Flora of New Zealand, Vol. V, Grasses. P. 362-8
  3. Kleemann S. G. L. & Gill G. S. 2008. Differences in the distribution and seed germination behaviour of populations of Bromus rigidus and Bromus diandrus in South Australia: adaptations to habitat and implications for weed management. Australian Journal of Agricultural Research 57(2) 213–219 doi:10.1071/AR05200
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