Weeds of Australia - Fact Sheet

Top Scientific Name Synonyms 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

Sporobolus natalensis (Steud.) Dur. & Schinz.

Synonyms

Sporobolus capensis (P.Beauv.) Kunth var. laxus Nees
Sporobolus indicus (L.) R. Br. var. laxus (Nees) Stapf
Vilfa natalensis Steud.

Family

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

Common Names

giant rat's tail grass, giant rats tail grass, giant rats-tail grass, giant ratstail grass, GRT, GRT grass

Origin

Native to central and southern Africa (i.e. Ethiopia, Kenya, Tanzania, Uganda, Cameroon, Zambia, Botswana, Namibia and South Africa).

Naturalised Distribution

This species is becoming widely distributed in the eastern parts of Australia. It is most commonly found in the coastal regions of southern Queensland and northern New South Wales. Scattered infestations also occur in the coastal districts of central and northern Queensland, near Sydney in New South Wales, and near Darwin in the Northern Territory.

Habitat

A weed of pastures, roadsides, disturbed sites, open woodlands, grasslands, parks, footpaths and lawns in sub-tropical, tropical and sometimes also warmer temperate regions.

Habit

An upright (i.e. erect) and long-lived (i.e. perennial) grass growing 60-170 cm tall, and forming large tussocks.

Distinguishing Features

• an upright and long-lived grass growing 60-170 cm tall and forming large tussocks.
  
  
• its very long and narrow leaf blades (20-50 cm long and 2-4 mm wide) may be flat or somewhat rolled.
  
  
• its elongated seed-heads (20-30 cm long and about 3 cm wide) have many branches.
  
  
• these seed-head branches are initially held closely to the stem, but become more open and slightly drooping as they mature.
  
  
• each of these branches bears numerous tiny flower spikelets (1.5-2 mm long).

Stems and Leaves

The flowering stems (i.e. culms) are relatively slender, but somewhat wiry.

The leaves are very thin (i.e. linear) with a leaf sheath, which partially encloses the stem, and a spreading leaf blade that may droop towards the ground. The leaf sheaths are hairless (i.e. glabrous) and the leaf blades (25-50 cm long and 2-4 mm wide) may be flat or somewhat rolled (i.e. convolute). The leaf blades are also hairless (i.e. glabrous) and have pointed tips (i.e. acuminate apices). Where the sheath meets the leaf blade there is a tiny membrane topped with a fringe of hairs up to 0.4 mm long (i.e. the ligule is a ciliated membrane).

Flowers and Fruit

The seed-heads are borne at the top of the flowering stems (i.e. culms) and are initially thin and elongated in appearance (i.e. spiciform), but become more open and droop slightly as they mature. These seed-heads (20-30 cm long and about 3 cm wide) have numerous relatively long (3-7 cm long) branches. Each of these branches bears numerous tiny, densely packed, elongated (i.e. lanceolate) or oval (i.e. elliptic) flower spikelets (1.6-2.3 mm long) almost to its base. The dark green or greyish-green flower spikelets (1.6-2.3 mm long) contain a single tiny flower (i.e. floret) inside two bracts (i.e. glumes). The lower bract (i.e. glume) is 0.5-0.8 mm long and the upper bract (i.e. glume) is 0.8-1.3 mm long (i.e. at least half the length of the flower spikelet). Flowering occurs during spring, summer and autumn (i.e. from October through to July).

The tiny seeds (i.e. grains or caryopses) turn yellowish-brown or reddish-brown in colour as they mature. These seeds (0.7-0.8 mm long and up to 0.6 mm wide) are oval (i.e. ellipsoid) or egg-shaped (i.e. obovoid) and separate from the remainder of the flower spikelet at maturity (i.e. the pale coloured old glumes remain on the seed-head).

Reproduction and Dispersal

This species produces large quantities of tiny seeds.

These seeds become somewhat sticky when wet, and may be spread after becoming attached to animals, clothing and vehicles. They may also be dispersed by water, in mud, and in contaminated agricultural produce (e.g. fodder and pasture seed lots).

Environmental Impact

Giant rat's tail grass (Sporobolus natalensis) is a significant environmental weed in Queensland and northern New South Wales, and was recently listed as a priority environmental weed in at least one Natural Resource Management region. It invades native grasslands, open woodlands, conservation reserves and wetland areas. When fully established in an area, it can form a grass monoculture, excluding native plants and reducing biodiversity of native groundcover species. This can also have an impact on native herbivores, which find the plants unpalatable.

Giant rat's tail grass (Sporobolus natalensis) is listed among among the exotic perennial grass species whose invasion of native plant communities in New South Wales has been listed as a "key threatening process". Along with Sporobolus pyramidalis, this species is ranked among the top 25 environmental weeds in south-eastern Queensland. It is also thought to pose a significant threat to rangeland biodiversity in central and northern Queensland, and heavy infestations may also increase fire intensity in sensitive environmental areas. The Giant rat's tail grasses (Sporobolus natalensis and Sporobolus pyramidalis) are already of concern in several conservation areas in Queensland.

Other Impacts

Giant rat's tail grass (Sporobolus natalensis) is a serious weed of pastures in the coastal districts of Queensland and northern New South Wales. It is of low palatability to livestock and can greatly reduce the productivity of agricultural land by completely displacing desirable pasture species. This reduction in productivity can be exhibited in reduced stocking capacities, longer periods of time to record adequate weight gains in beef cattle, and higher costs in milk production on dairy farms. The economic costs incurred in managing this species with herbicides are also quite high, and heavily infested areas have reduced land values. Mature leaf blades and stems are tough for animals to graze, and have been known to loosen the teeth of cattle and horses.

Legislation

This species is declared under legislation in the following states and territories:

• Queensland: Class 2 - landowners must take all reasonable steps to keep land free of this species (throughout the entire state). It is also illegal to sell a declared plant or its seed in this state.
  
  
• Western Australia: Prohibited - on the prohibited species list and not permitted entry into the state.

Management

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

• the Biosecurity Queensland Fact Sheet on giant rats tail grass and other weedy Sporobolus species, which is available online at http://www.dpi.qld.gov.au.

Similar Species

Giant rats-tail grass (Sporobolus natalensis ) is very similar to other introduced rats-tail grasses (Sporobolus spp.) including another species known as giant rats-tail grass (Sporobolus pyramidalis), Parramatta grass (Sporobolus africanus), giant Parramatta grass (Sporobolus fertilis ) and American rats-tail grass (Sporobolus jacquemontii ). It is also similar to some native species such as the slender rats-tail grasses (Sporobolus creber and Sporobolus elongatus). Distinguishing between these species is often very difficult and a specialist may need to be consulted, however the following is a guide to the differences that may be apparent:

• giant rats-tail grass (Sporobolus natalensis) is a relatively large plant (60-150 cm tall) with relatively large spike-like (i.e. spiciform) seed-heads (20-30 cm long). These seed-heads have numerous relatively long branches (30-70 mm long) that usually spread away from the main stem. These branches are normally densely arranged and the seed-head is un-interrupted. Its flower spikelets are moderately-sized (1.6-2.3 mm long).
  
  
• giant rats-tail grass (Sporobolus pyramidalis) is a relatively large plant (usually 90-200 cm tall) with relatively large pyramid-shaped (i.e. pyramidal) seed-heads (20-45 cm long). These seed-heads have numerous relatively long branches (50-100 mm long) that stiffly spread away from the main stem. Its flower spikelets are moderately-sized (1.7-2.2 mm long).
  
  
• Parramatta grass (Sporobolus africanus) is a relatively small plant (usually less than 50 cm tall) with relatively small spike-like (i.e. spiciform) seed-heads (6-35 cm long). These seed-heads have numerous short branches (10-20 mm long) that are usually held closely (i.e. appressed) to the main stem. These branches are normally densely arranged and the seed-head is mostly un-interrupted (except occasionally at the base). Its flower spikelets are relatively large (2-2.8 mm long).
  
  
• giant Parramatta grass (Sporobolus fertilis) is a relatively large plant (usually 80-160 cm tall) with relatively large spike-like (i.e. spiciform) seed-heads (15-50 cm long). These seed-heads have numerous moderately long branches (20-80 mm long) that are held closely (i.e. appressed) to the main stem or slightly spreading. These branches are normally densely arranged and the seed-head is mostly un-interrupted (except occasionally at the base). Its flower spikelets are relatively small (1.5-2 mm long).
  
  
• American rats-tail grass (Sporobolus jacquemontii) is a moderately-sized plant (usually 50-75 cm tall) with relatively small elongated seed-heads (8-25 cm long). These seed-heads have numerous relatively long branches (50-100 mm long) that usually spread away from the main stem. These branches are normally densely arranged and the seed-head is un-interrupted. Its flower spikelets are relatively small (1.5-2 mm long).
  
  
• slender rats-tail grass (Sporobolus creber) is a moderately-sized plant (usually less than 100 cm tall) with relatively long and very narrow spike-like (i.e. spiciform) seed-heads (18-60 cm long). These seed-heads have numerous short stiff branches (5-10 mm long) that are always held closely (i.e. appressed) to the main stem. These branches are normally widely spaced and the seed-head is interrupted (except near the top). Its flower spikelets are relatively small (1.2-1.7 mm long).
  
  
• slender rats-tail grass (Sporobolus elongatus) is a moderately-sized plant (usually 50-100 cm tall) with relatively long and narrow spike-like (i.e. spiciform) seed-heads (10-30 cm long). These seed-heads have numerous relatively long branches (40-80 mm long) that are usually held closely (i.e. appressed) to the main stem (sometimes slightly spreading). These branches are normally densely arranged and the seed-head is mostly un-interrupted (except occasionally at the base). Its flower spikelets are moderately-sized (1.5-2.3 mm long).