Bulbous Oatgrass

Arrhenatherum elatius var. bulbosum (Willd.) Spenner

Synonyms - Arrhenatherum avenaceum, Arrhenatherum bulbosum, Avena bulbosa, Avena elatior, Avena tuberosa, Holcus avenaceus.

Family: Poaceae.

Names:

Arrhenatherum is from the Greek arrhen meaning male and ather meaning awn and refers to the awn on the male floret.
Bulbous Oatgrass - because it superficially resembles oats with bulbs.

Other Names:

Bulbous False Oat
False Oatgrass
False Oat
Onion Couch - because the basal swollen internodes look like little onions.
Onion-rooted Twitch
Onion Twitch

Summary:

A loosely clumped, robust, almost hairless, perennial up to 1.5 m tall with a yellow stem base and bulbous corms.

Description:

Cotyledons:

One.

Leaves:

Blade - 400 mm long x 5-10 mm wide. Flat. Parallel sided. Hairless or sparsely hairy on the upper surface. Finely pointed.
Ligule - Membranous, prominent, small, translucent. Occasionally flat topped or fringed.
Auricles - None.
Sheath - Rounded on the back and smooth. Often reddish towards the base. Tubular.

Stems:

Erect. Loosely tufted or occasionally spreading. 1500 mm tall. Short whorled branches. Occasionally bent like a knee. Nodes occasionally hairy.

Flower head:

Loose and open panicle initially but becomes upright and compact with age and sometimes nodding. 120-300 mm long. Green or purplish when young.

Flowers:

Disarticulate above the glumes.
Spikelets - 7-11 mm long. On stalks that are usually shorter than the spikelet. Usually 2 flowered. Flattened.
Florets - 9 mm long. Lower one male. The upper bisexual.
Glumes - Broad, shiny, thin, translucent, pointed, rounded on back. Upper one has three nerves and is 8-11 mm long. Lower one has one nerve and is smaller at 5-7 mm long.
Palea - Narrower than lemma. 6-8 mm long. Hairy on keels.
Lemma - 8-11 mm. 5-9 nerved. Hairy near base, rough to touch above. Firm, translucent margins, rounded on back. Upper one awnless or is shortly awned near the top. Lower (male) one has a 18 mm, bent, twisted awn and arises from below the middle of the lemma.
Stamens -
Anthers -

Fruit:

Seeds:

Pale, 9 mm long x 2 mm wide with a bent awn that is about as long as the seed or 9 mm long.

Roots:

1 to several basal internodes swollen into a corm or a chain of corms. Yellowish.

Key Characters:

Biology:

Life cycle:

Perennial. Grows from seed and corm like swollen nodes at the base of the plant.

Physiology:

Corms are unpalatable to grazing animals but are often eaten by pigs.

Reproduction:

By seed and corms.

Flowering times:

December.

Seed Biology and Germination:

Vegetative Propagules:

Corms.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Origin and History:

Europe and western Asia.
Naturalised in most temperate areas.

Distribution:

ACT, NSW, QLD, SA, TAS, VIC, WA.
Occurs in the Jarrah Forest, Swan Coastal Plain and Warren regions in the high rainfall regions of WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate areas, Mediterranean.
Prefers high rainfall areas.

Soil:

Prefers summer moist soils and sands.

Plant Associations:

Significance:

Beneficial:

Ornamental. Fodder. Formerly used as a pasture grass

Detrimental:

Weed of vegetables, cultivation, disturbed areas, rotational crops, perennial crops, grasslands.

Toxicity:

Not recorded as toxic.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Related plants:

False Oatgrass (Arrhenatherum elatius) is smaller with green and white striped leaves and has no corms.

Plants of similar appearance:

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P36. Photo.

Black, J.M. (1978). Flora of South Australia. (Government Printer, Adelaide, South Australia). P164. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P36. Diagram.

Ciba Geigy (1981) Grass Weeds 2. CIBA GEIGY Ltd, Basle, Switzerland. P21. Diagrams.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #129.1.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P940.

Moerkerk, M.R. and Barnett A.G. (1998) More Crop Weeds. (R.G and F.J. Richardson, Melbourne). P26. Photos. Diagrams.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P25. Diagrams.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.