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 Similar Species

Scientific Name

Piptochaetium montevidense (Spreng.) Parodi

Synonyms

Caryochloa montevidensis Spreng.

Family

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

Common Names

piptochaetium, Uruguayan rice grass, Uruguayan rice-grass, Uruguayan ricegrass

Origin

Native to South America (i.e. southern Brazil, southern Ecuador, Venezuela, Bolivia, Peru, northern and central Argentina, central Chile, southern Uruguay and southern Paraguay).

Naturalised Distribution

This species is only known to have become naturalised at Altona, near Melbourne in southern Victoria. However, it appears to have been accidentally eradicated when it was covered by landfill.

Habitat

In its native range it frequently grows along rivers, in grasslands and in rocky sites. In Australia, where it has only been recorded from a single site, in was growing in a grassland along with native grasses (i.e. Themeda spp. and Austrostipa spp.).

Evidence from other parts of the world suggests that this species will grow in crops, along roads and streambanks, in urban areas and in natural environments such as grassy woodlands and lowland grasslands.

Habit

A long-lived (i.e. perennial) tussock-forming grass usually growing 0.3-0.6 m tall.

Distinguishing Features

• a long-lived tussock-forming grass usually growing 0.3-0.6 m tall.
  
  

• its leaf blades (5-15 cm long and 0.5-1 mm wide) are extremely narrow and are usually folded or rolled inwards.
  
  

• its elongated seed-head (2-10 cm long and 1-2 cm wide) usually have several relatively short branches with numerous flower spikelets.
  
  

• these flower spikelets (3-3.5 mm long) are oblong in shape and are topped with an awn 7-10 mm long.
  
  

• the 'seeds' detach from the seed-head when mature, leaving behind the two outer bracts.

Stems and Leaves

The stems are generally unbranched and hairless (i.e. glabrous).

The leaves consist of a sheath, which partially encloses the stem, and a spreading leaf blade. They are tufted together at the base of the plant and alternately arranged along the stems. The leaf sheaths can be hairless (i.e. glabrous) to somewhat hairy (i.e. puberulous or pubescent) and where the leaf sheath meets the leaf blade there is a tiny membranous structure (i.e. membranous ligule) 0.5-2 mm long. The leaf blades (5-15 cm long and 0.5-1 mm wide) are extremely narrow (i.e. filiform) and are usually folded (i.e. conduplicate) or rolled inwards (i.e. involute or convolute). They have entire margins and hairless (i.e. glabrous) or somewhat hairy (i.e. pubescent) surfaces.

Flowers and Fruit

The elongated seed-head (2-10 cm long and 1-2 cm wide) is branched, but the branches are relatively short and held close to the main stem (i.e. the inflorescence is a contracted panicle). Each of the seed-head branches bears numerous small flower spikelets on individual stalks (i.e. pedicels). These flower spikelets (3-3.5 mm long) consist of a pair of bracts (i.e. glumes) and a single tiny flower (i.e. floret). They are oblong in shape, flattened and purplish in colour when young. The floret consists of a pair of hardened bracts (i.e. lemma and palea), three stamens, and an ovary topped with two feathery stigmas. The outer bract (i.e. lemma) is dark brown or black in colour and topped with an awn 7-10 mm long. Flowering occurs mainly during spring and early summer (i.e. from September to December).

The florets (about 2 mm long) detach from the seed-head when mature, leaving behind the two outer bracts (i.e. glumes), and have a sharp hairy base (i.e. pubescent callus). The 'seed' (i.e. caryopsis or grain) remains contained within the hard floral bracts (i.e. lemma and palea). This small 'seed' is almost round in shape (i.e. orbicular) and is about 0.6-0.7 mm long. The seeds develop during summer and are usually shed by early autumn.

Reproduction and Dispersal

Uruguayan rice grass (Piptochaetium montevidense) reproduces by seed. These seeds are dispersed by wind and also by grazing animals ingesting the plant and depositing the viable seed elsewhere. They can also be spread in contaminated soil and agricultural produce.

Environmental Impact

Uruguayan rice grass (Piptochaetium montevidense) is on the Alert List for Environmental Weeds, a list of 28 non-native plants that threaten biodiversity, and is regarded as a potential environmental weed in Victoria and in other parts of south-eastern Australia. Because it forms dense tussocks, is stimulated by fire and is resistant to grazing, this species may have the ability to out-compete native plants, especially in disturbed or heavily grazed areas. Uruguayan rice grass (Piptochaetium montevidense) is also closely related to several other South American stipoid grasses that have become major environmental weeds in Australia (e.g. Nassella spp.).

Stipoid grasses, such as Uruguayan rice grass (Piptochaetium montevidense), generally invade sites that are highly degraded and have a history of disturbance. However, they can also invade relatively undisturbed vegetation. Uruguayan rice grass (Piptochaetium montevidense) has been estimated to have a potential distribution of 600,000 hectares throughout Victoria and New South Wales, and may also have the potential to invade parts of South Australia, south-western Western Australia and eastern Queensland.

Other Impacts

Uruguayan rice grass (Piptochaetium montevidense) has been reported as a weed of forest legumes and timothy grass in Canada and is also regarded as a weed in its native Brazil. The land uses potentially at risk from the spread of this species in Australia are thought to include crops, pastures and horticulture. As Uruguayan rice grass (Piptochaetium montevidense) has already been reported growing in a native grassland in Victoria, and has a good climate match for many parts of south-eastern Australia, it is probably of greatest threat to the grazing industry in the temperate regions of Australia.

Legislation

Not declared or considered noxious by any state government authorities.

Similar Species

Uruguayan rice grass (Piptochaetium montevidense) is very similar to several other introduced stipoid grasses (i.e. Nassella spp., Achnatherum spp. and Jarava plumosa). These species are difficult to distinguish and a dedicated text or expert should be consulted. However, Uruguayan rice grass (Piptochaetium montevidense) can be separated from most of these species by its smaller and broader 'seed' (about 2 mm long) that is topped with a relatively short awn (less than 10 mm long).

It is also similar to many of the native speargrasses (Austrostipa spp.), but once again these species usually have much longer awns.

Refer to the grasses identification table on pages 2-3 of the CRC Weed Management Guide for assistance in distinguishing Uruguayan rice grass (Piptochaetium montevidense) from many of these other grass species.