Whisky grass

Andropogon virginicus
infestation (Photo: Sheldon Navie)
habit (Photo: Sheldon Navie)
base of plant, with tufts of leaves and several upright stems (Photo: Sheldon Navie)
upper part of stem, with leaves and young seed-heads (Photo: Sheldon Navie)
mature seed-heads (Photo: Sheldon Navie)
leafy bracts of a mature seed-head (Photo: Sheldon Navie)
Grass
Basal
Simple
White
Green
Green

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.

Common names 
Also known as: Whisky grass, andropogon, beard grass, broom sedge, bluestem, whiskey grass, yellow bluestem,
Family 
Poaceae
Deciduous 
No
Flowering time 
Autumn-Summer
Native/Exotic 
Exotic
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).
Notifiable 
No
Council declaration 
Class R – Reduce populations
Known 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.

Impact and control methods 

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, 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. 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 Conservation Area).

Stem 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 fruits 

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.

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.