grader grass

Themeda quadrivalvis
Grass
Alternate
Simple
Brown
Green

An upright and short-lived grass growing 50-200 cm tall. Its stems, leaves and seed-heads turn reddish-brown or golden-brown in colour as they mature. Its seed-heads consist of many drooping, fan-shaped flower clusters interspersed with short 'leaves'. The mature seeds (4.5-5.5 mm long) have a cluster of hairs at the base and are topped with a large twisted awn (10-45 mm long).

Common names 
Also known as: grader grass, habana grass, , oatgrass, kangaroo grass,
Family 
Poaceae
Deciduous 
No
Flowering time 
Summer - Winter
Native/Exotic 
Exotic
Origin 
Native to the Indian sub-continent (i.e. India and Nepal) and possibly also parts of south-eastern Asia (i.e. Thailand, Vietnam, Myanmar and Indonesia).
Notifiable 
No
Council declaration 
SIL – Special Investigation List
Known distribution 

This species is widely distributed throughout the coastal and sub-coastal regions of the Northern Territory and Queensland. Scattered populations are also found in the northern parts of Western Australia and in the coastal districts of northern New South Wales. Also naturalised in some parts of the USA (i.e. California, Kansas, Louisiana and Florida), the Caribbean, southern South America, Africa, western Asia, China, the Mascarenes (i.e. La Réunion) and on some Pacific islands (i.e. Fiji and New Caledonia).

Habitat 

A weed of roadsides, disturbed sites, waste areas, open woodlands, grasslands, pastures and crops that is mainly found in tropical and sub-tropical regions.

Habit 

A short-lived (i.e. annual) tufted grass with an upright (i.e. erect) habit that usually grows 50-200 cm tall.

Impact and control methods 

rangelands, particularly in areas that are overgrazed or disturbed. It replaces native plants and forms tall thickets that can cover large tracts of land. Due to its greater biomass than the native plants it replaces, and hence its higher fuel loads, grader grass (Themeda quadrivalvis ) alters the fire regime. It does this by carrying more wildfires that are of a much greater intensity than the native plants are used to. Each of these hot fires, during the late dry season, cause a thinning of the native woodlands and eventually the number of trees in the ecosystem are reduced, resulting in a change from native savanna woodlands to exotic grasslands. It is currently causing most concern in the semi-arid rangelands of northern Queensland and the Northern Territory, where it is abundant and continuing to spread. However, it also appears in the list of the top 200 most invasive plants of south-eastern Queensland, and is in the New South Wales North Coast environmental weed list. It is also seen as a potentially significant threat to the Kimberley region in northern Western Australia, though it is not yet very widespread in this region. Grader grass (Themeda quadrivalvis) is also an important weed of crops in many parts of northern Australia. It is particularly troublesome in sugar cane, but can also be found in lucerne and other legume seed crops. It is regarded as a major weed of crops in coastal northern and central Queensland, and is also a minor crop weed in inland central Queensland and the Northern Territory.This species is a also very common weed of roadsides, where it can quickly become a safety hazard by reducing visibility on corners.

Stem and leaves 

Plants are robust with several upright stems (i.e. erect culms) being produced from each rootstock. The stems (4-6 mm thick) are green at first, hairless (i.e. glabrous), and turn reddish-brown or golden-brown in colour as they mature. The alternately arranged leaves consist of a leaf sheath, which partially encloses the stem, and a narrow (i.e. linear) leaf blade (7-60 cm long and 1-7 mm wide). These leaves are folded in the bud and green at first, but also turn brownish in colour with age. The leaf margins are flat or sometimes rolled under (i.e. recurved) and the leaf blades have pointed tips (i.e. acute or acuminate apices). Where the leaf sheath meets the leaf blade there is a small membranous structure (i.e. membranous ligule) 1-3 mm long.

Flowers and fruits 

The seed-heads (15-60 cm long) have several small branches that are interspersed with short 'leaves' (i.e. spathes). They turn brown or slightly reddish in colour and become somewhat drooping in nature as they mature. These seed-heads consist of several complex triangular-shaped or fan-shaped flower clusters (1-3 cm long), enclosed in leafy bracts (about 2 cm long), that contain both fertile and sterile flower spikelets. The fertile flower spikelets (5-6 mm long) are oval (i.e. elliptic) or almost cylindrical (i.e. sub-terete) in shape. They have one tiny fertile flower (i.e. floret), one tiny sterile flower, and a pair of bracts (i.e. glumes) 4.5-6 mm long. The bracts (i.e. glumes) are elongated in shape (i.e. lanceolate) and stiffly hairy (i.e. setose) in the upper half. Flowering occurs mainly during summer and autumn, but may also occur during winter. The 'seeds' (i.e. grains or caryopses) are brown in colour with an obvious cluster of reddish hairs at the base (i.e. callus). These 'seeds' (4.5-5.5 mm long) are topped with a relatively large, conspicuous, bent and twisted, awn (10-45 mm long) and are enclosed within two hairless (i.e. glabrous), smooth, bracts (i.e. a palea and lemma).

Reproduction and dispersal 

This plant only reproduces by seed.Seeds are spread by animals and vehicles, in clothing and mud, and as a contaminant of agricultural produce. They are also commonly dispersed during soil moving activities, such as the grading of roads (hence the common name "grader grass").

Similar species 

Grader grass (Themeda quadrivalvis) is very similar to the native kangaroo grass (Themeda triandra) and reasonably similar to native oatgrass (Themeda avenacea) and lesser tanglegrass (Themeda arguens). These species can be distinguished by the following differences: grader grass (Themeda quadrivalvis) is a moderately-sized to relatively large short-lived (i.e. annual) grass growing up to 1.8 m tall. Its individual flower spikelets are relatively small (4-7 mm long), stiffly hairy (i.e. setose) in the upper half, and its seeds are topped with a relatively fine awn (10-45 mm long).kangaroo grass (Themeda triandra ) is a moderately-sized long-lived (i.e. perennial) grass usually growing less than 1 m tall. Its individual flower spikelets are moderately-sized (6-14 mm long), hairless (i.e. glabrous) or slightly hairy (i.e. hispid), and its seeds are topped with a relatively large awn (25-70 mm long).native oatgrass (Themeda avenacea) is a large long-lived (i.e. perennial) grass often growing up to 2 m tall. Its individual flower spikelets are very large (13-30 mm long), densely hairy (i.e. villous), and its seeds are topped with a large and robust awn (40-100 mm long).lesser tanglegrass (Themeda arguens ) is a large short-lived (i.e. annual) grass growing up to 3 m tall. Its individual flower spikelets are moderately-sized (6-11 mm long), softly hairy (i.e. pubescent), and topped with a large and robust awn (50-90 mm long).

Replacement species 
Themeda triandra