Weeds of Australia - Fact Sheet

Top Scientific Name Family Common Names Origin Naturalised Distribution Habitat Habit Distinguishing Features Stems and Leaves Flowers and Fruit Reproduction and Dispersal Environmental Impact Other Impacts Legislation Management Similar Species

Scientific Name

Andropogon virginicus L.

Family

Gramineae (South Australia)
Poaceae (Queensland, New South Wales, the ACT, Victoria, Tasmania, Western Australia and the Northern Territory)

Common Names

andropogon, beard grass, broom sedge, broom-sedge, broomsedge, broom-sedge bluestem, broomsedge bluestem, broomstraw, sedge grass, whiskey grass, whisky grass, yellow bluestem

Origin

Native to North America (i.e. south-eastern Canada, eastern USA and Mexico), Central America (i.e. Belize, Costa Rica, Guatemala, Honduras, Nicaragua and Panama), the Caribbean and tropical South America (i.e. Colombia).

Naturalised Distribution

Widely naturalised in eastern Australia (i.e. in south-eastern Queensland, eastern New South Wales and some parts of Victoria). It was also naturalised in the ACT, but has not been collected there for many years.

Also naturalised in New Zealand, Hawaii and beyond its native range in south-western USA (i.e. California).

Habitat

A weed of roadsides, disturbed sites, waste areas, pastures, wetlands, grasslands and open woodlands in sub-tropical and warmer temperate regions.

Habit

A long-lived (i.e. perennial) tufted grass usually growing 0.5-1 m tall, but occasionally reaching up to 1.5 m in height.

Distinguishing Features

• a long-lived tufted grass usually growing 0.5-1 m tall.
  
  

• the older stems and leaves turn reddish-brown or brownish-orange in colour during summer.
  
  

• its elongated leaves (10-40 cm long and 2-5 mm wide) can be either flat or folded.
  
  

• where the leaf sheath meets the leaf blade there is a small membranous structure topped with hairs.
  
  

• its leafy seed-heads consist of several to numerous pairs of tiny branches (2-3 cm long) that are partly enclosed by brownish leafy bracts 2.5-6 cm long.
  
  

• its flower-spikelets fall off entire at maturity, usually with numerous long white silky hairs.

Stems and Leaves

The upright (i.e. erect) stems are branched and mostly hairless (i.e. glabrous). The older stems and leaves turn reddish-brown or brownish-orange in colour during summer.

The leaves consist of a hairy to hairless (i.e. pubescent to glabrous) leaf sheath, which partially encloses the stem, and a spreading leaf blade. These leaf blades can be either flat or folded (10-40 cm long and 2-5 mm wide) and are hairless except for some long (i.e. pilose) hairs that are occasionally found towards the base of their upper surfaces. Where the leaf sheath meets the leaf blade there is a small membranous structure topped with hairs (i.e. a ciliate ligule).

Flowers and Fruit

The leafy seed-heads are long and narrow and consist of several to numerous pairs (occasionally triplets or quadruplets) of tiny branches (i.e. racemes). Each pair of branches (2-3 cm long) is partly enclosed by brownish or bronze-coloured leafy bract (i.e. spathe) 2.5-6 cm long. The stalks of these branches are very slender and they bear several flower spikelets among clusters of long white hairs (5-10 mm long). The flower spikelets are arranged in pairs, with one of the flower spikelets in each pair being stalkless (i.e. sessile) and the other being borne on a short stalk (i.e. pedicel). The stalkless or sessile spikelet (2.5-4 mm long and about 1 mm wide) has both male and female parts (i.e. it is bisexual and fertile), while the stalked or pedicellate spikelet is sterile and is sometimes absent entirely (i.e. only a stalk is present). The stalkless spikelets consist of a pair of bracts (i.e. glumes) and two tiny flowers (i.e. florets), only one of which is fully formed. The fully formed floret has only one obvious floral bract (i.e. a lemma) that is topped with a delicate and straight awn (1-2.5 cm long), three stamens, and an ovary topped with a two-branched feathery stigma. flowering occurs from autumn through to summer (i.e. from March to December).

The flower-spikelets fall off entire at maturity, usually with numerous of the long white silky hairs, and the small 'seed' (i.e. caryopsis or grain) remains hidden within the floral bracts.

Reproduction and Dispersal

This species reproduces mainly by seed. These light seeds may be easily spread by wind and water and can also adhere to animals, clothing and vehicles. They are also commonly dispersed to new areas when seeding plants are slashed or mown, and can also move longer distances in contaminated soil and agricultural produce.

Environmental Impact

Whisky grass (Andropogon virginicus) is regarded as an environmental weed in New South Wales and Queensland. This species invades open woodlands, grasslands, forests and other native vegetation in eastern Australia. However it prefers very open sunny areas and is particularly common along tracks and roadsides. Unlike many exotic weeds, it is also known to invade native plant communities that are extremely deficient in nutrients. Whisky grass (Andropogon virginicus) is highly flammable at certain times of the year and can significantly alter the fire regime in areas where it invades. It is also known to affect other ecosystem-level functions (e.g. it lowers soil evaporation and causes accelerated erosion).

 

This species is currently of most concern in eastern New South Wales, where it is seen as a threat to the integrity of several plant communities and the survival of some rare and threatened species. It appears on numerous local and regional environmental weed lists in New South Wales (e.g. in the wider Sydney and Blue Mountains region, in the North Coast, Central Coast and South Coast regions, and in the Warringah, Manly, Pittwater and Byron Councils) and also occurs in several conservation areas in this state (e.g. Warriewood Wetlands, Marramarra National Park, Muogamarra Nature Reserve and Rawdon Creek Nature Reserve). 

 

The "invasion of native plant communities by exotic perennial grasses" was recently listed as a "key threatening process" in New South Wales, and whisky grass (Andropogon virginicus) is one of the species specifically mentioned in this listing. Whisky grass (Andropogon virginicus) is also mentioned as being a significant threat or principal weed species in eucalypt grassy forest/woodlands of the New England Tableland bioregion and swamp sclerophyll forests on coastal floodplains, both of which are endangered ecological communities in New South Wales.

 

Grassy weeds, such as whisky grass (Andropogon virginicus), are also degrading the habitat occupied by the vulnerable Charmhaven apple (Angophora inopina) and may be having a direct impact on the regeneration of this species. It has also been recorded as a weed threat at some of the sites occupied by the vulnerable downy wattle (Acacia pubescens) in the Sydney region.

In Queensland, whisky grass (Andropogon virginicus) is mainly a problem in the south-eastern corner of the state. It is ranked among the top 200 most invasive plant species in this region and has been recorded in conservation areas on the Gold Coast (e.g. in the Pimpama River Conservation Area).

 

Overseas, whisky grass (Andropogon virginicus) is also a serious problem in Hawaii and parts of mainland USA. It is common and often dominant along roadsides and in disturbed dry to mesic forests and shrublands in Hawaii. It also forms continuous cover in boggy, open mesic or dry habitats in the USA. These dense stands persist as a result of competition and allelopathy, and provide excellent fuel for fires, which further stimulate its invasion. Studies in mainland USA have found that both fire intensity and area of land burnt are higher in areas where whisky grass (Andropogon virginicus) occurs.

Other Impacts

Because this species is of low nutritional value to livestock, it can reduce the productivity of invaded pastures. It may also be a fire hazard (i.e. it can increase the damage caused by bushfires).

Legislation

This species is not declared or considered noxious by any state or territory government in Australia.

Management

For information on the management of this species see the following resources:

• the Whisky grass page on the South Coast Weeds website at http://www.esc.nsw.gov.au/Weeds/index.asp.

Similar Species

Whisky grass (Andropogon virginicus) is very similar to the native firegrass (Schizachyrium fragile) and the recently introduced Schizachyrium microstachyum. However, these grasses have their seed-head branches (i.e. racemes) borne singly instead of in pairs.

It may occasionally also be confused with grader grass (Themeda quadrivalvis) and the native kangaroo grass (Themeda triandra), which also turn reddish-brown in colour. However these species have their flower spikelets arranged in drooping triangular-shaped clusters, with very large and twisted awns.