Coolatai Grass

Hyparrhenia hirta (L.) Stapf

Synonyms - Andropogon hirtus

Family: Poaceae

Names:

Hyparrhenia is from the Greek arrhenos meaning male and hypo meaning below and refers to the lower male floret of the fertile spikelet.
Hirta means hairy.
Coolatai refers to the town in northern NSW where it was planted in the 1890's for erosion control.

Other Names

Tambookie Grass

Summary:

A densely tufted, summer active annual or perennial grass, 0.3-1.2 m tall with awned, silky-hairy, grey green spikelets carried in many pairs of racemes, in an open panicle and each raceme with a leaf-like bract at the base. The seed head becomes fluffy when dry. It has pale grey-green to blue-green leaves and often forms tussocks.

Description:

Cotyledons:

One.

First leaves:

Leaves:

Blade - Pale grey green to blue green, 100-300 mm long x 1-3 mm wide. Fine tapering pointed tip, parallel sides, sheathing base. Surface flat or sometimes with rolled edges, hairless or with a few scattered long hairs. Midrib whitish. Leaves rolled in the bud.
Ligule - Membranous, 2-3 mm long with tufts of hairs on each side
Auricles - None.
Sheath - Lower ones usually somewhat flattened. Upper ones are cylindrical. Hairless or rarely with a few hairs.

Stem leaves - Leaf-like bracts at the base of each pair of racemes.

Stems:

Erect, branched.

Flower head:

Many branched elongated loose panicle, 150- 400 mm long. There is a leaf like bract(spathe) at the base of each branch which ends in a pair of grey, silky hairy racemes that are on slender stalks. The bract is narrowly egg shaped tapering to a fine point, 30-80 mm long, and turn reddish with age and are hairless or with a few long scattered hairs that turn reddish. Racemes are whitish or grey-hairy, paired, 15-50 mm long with 5-8 awns (and spikelets) per raceme. One raceme is stalkless and the other on a hairy stalk. There is a pair of sterile male spikelets at the base of the lower or both racemes.
Racemes erect or nodding.
Flower head expanded and fluffy when dry.

Flowers:

Spikelets - In pairs, flattened on a jointed fragile main axis (rachis). 1 is sessile, usually awned, with 2 florets, the lower one male and the upper fertile and bisexual. The other pedicellate, awnless and male or sterile, Sessile spikelets 1-few in each raceme flattened on the back with the base elongated into a hairy sharp callus. Spikelets of the lowest pair(s) on a raceme similar, awnless and sterile or male. Spikelets fall with an axis joint
Sessile Spikelet - narrowly oblong, 4-6 mm long, fertile, bisexual

Glumes - Equal, thin, no distinct keel, hairy. Upper glume thinner than lower glume, 3 veined, boat shaped with a tiny point (mucro). Lower glume 9-11 veined, loosely hairy, 2 lobed or flat tip.
Palea - Absent
Lemma - 2, Lower one narrowly oblong, 2 veined, rounded tip, translucent and almost as long as the glumes. Fertile upper lemma small, parallel sided, stalk like, translucent base, edges and lobes, 4 mm long, with 2 short lobes and a hairy, bent, slender awn that is 15-25 mm long arising from between the lobes.
Pedicellate Spikelet - greenish or reddish, male, hairy or hairless, 4-7 mm long, narrowly oblong with an acute tip, awnless.

Glumes - Equal, similar to those on sessile spikelet
Palea - Usually absent
Lemma - 2, Lower one 2 veined. Upper lemma 1 or 0 veined.
Florets - 2.
Callus - Hairy

Stamens -
Anthers -

Seeds:

Oblong grain.

Roots:

Fibrous and deep.

Key Characters:

Plants usually less than 1000 mm tall.
Inflorescence not enclosed in leaf sheath.
Culms much branched from the upper nodes.
Spathes supporting pairs of racemes.
Internodes of the raceme axis and pedicels are slender.
Raceme breaks up at maturity, the spathe and lower sterile part may be persistent.
Racemes paired on very slender peduncles in the ultimate spathe
Callus subacute or acuminate and pungent.
Rachis of inflorescence hollowed on the inner face and sessile spikelets sunken into these cavities.
Basal sterile spikelets not forming an involucre around the fertile spikelet.
Spikelets in pairs, one sessile and the other pedicellate and dissimilar in sex.
Only one spikelet fertile.
Lower 1-few pairs of spikelets usually sterile.
Mature spikelets fall entire.
Fertile spikelets cylindrical and slightly flattened dorsally with 2 florets.
5-8 awned spikelets per raceme.
Awns 15-35 mm long, hairy on the lower part.
Glume rigid and longer than the lemma (excluding the awn) and as long as spikelet and enclosing the florets.
Lemma membranous.
Upper lemma of sessile spikelet awned
Lower floret of sessile spikelet sterile.
Based on keys by J.M. Black, S.W.L. Jacobs and C.A. Wall, T.D. Macfarlane.

Biology:

Life cycle:

Perennial but may act as and annual.
Summer active and grows most rapidly over spring and after rain in summer.

Physiology:

C4 plant with high water use efficiency.
It is drought tolerant and has high growth rates in moist conditions when it is warm to hot.
Susceptible to frost damage.
Doesn't tolerate waterlogging.
Optimum growth occurs between 26 and 380C.
Seedlings can grow at temperatures of 400C.

Reproduction:

By seed.

Flowering times:

November to March usually with some to July in WA.
Summer in NSW.
May and December in SA

Seed Biology and Germination:

Seed will germinate over a wide range of temperatures, light conditions, pH and under marginal water stress.
Germination doesn't occur below 50C or above 450C.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spreads along roadsides. Soil movement, mowing and water appear to be the main agents of dispersal.
It does not appear to tolerate grazing in the WA environment.

Origin and History:

Africa, Mediterranean to Pakistan.
It was initially introduced for erosion control in the Coolatai area in northern NSW during the 1890's.
It was then planted as a pasture grass but generally not very successful unless it is kept short by grazing, mowing or fire.

Distribution:

ACT?, NSW, QLD, NT, SA, TAS, VIC, WA.
Avon Wheatbelt, Esperance Plains, Geraldton Sandplains, Jarrah Forest, Swan Coastal Plain and the Warren in WA.
It infests large areas of southern Queensland, Northern New South Wales, Victoria and South Australia.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate. Most prolific in areas with 175-600 mm rainfall.
Prefers full sun but will tolerate semi shade

Soil:

Sands and sandy loams.

Plant Associations:

Dry woodland or grassland.

Significance:

Spreading rapidly on roadsides and rail verges in the south west of WA.
Invades remnant bushland and disturbed areas.
Potential to invade most of the WA agricultural area apart from the far southwest (i.e. south of the Bunbury to Albany line) 559.

Beneficial:

Fodder.

Detrimental:

Roadside weed, invades disturbed bushland.
Potentially a serious environmental weed that can reduce the cover and species richness of native flora.
Changes fire intensity and frequency.

Toxicity:

None recorded.

Symptoms:

Treatment:

Legislation:

None.

Management and Control:

Few if any herbicides registered.
Burning and mowing generally make the infestation worse unless they are combined with herbicides or grazing.
Heavy, constant grazing over a few years provides control.
Glyphosate applied to actively growing plants usually provides good control but may need a few annual applications in spring to control established infestations.

Thresholds:

Not recorded as a weed of cultivated crops.

Eradication strategies:

Mow or burn then spray actively growing regrowth with 1000 mL glyphosate(450g/L) plus 250 mL Pulse® per 100 L water in spring (or summer through to autumn if the plants are not drought stressed). Repeat annually until no more seedlings appear then replant to scrub or perennial pasture species.
Tussocks can be manually removed but control of seedlings by hand weeding is difficult.

Herbicide resistance:

None recorded.

Biological Control:

Related plants:

Tambookie Grass Hyparrhenia filipendula var. filipendula is in NSW and QLD has 1-2 awned spikelets in each raceme and the awns are longer at 40-50 mm long. In WA Coolatai Grass (Hyparrhenia hirta)is often referred to as Tambookie Grass.
Hyparrhenia rufa ssp. altissima is in NSW and QLD and has 9-10 awned spikelets in each raceme rather than 5-7.

Plants of similar appearance:

Grasses.
Kangaroo Grass (Themeda spp.)
Wallaby Grass (Austrodanthonia spp.)

References:

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P245. Diagram.

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 4. P446. Diagram.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P56. Photo.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). 521.2.

Marchant et al (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P965.

Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P109.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P58. Diagram.

Acknowledgments:

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