giant rat's tail grass

Sporobolus pyramidalis
Grass
Alternate
Simple
Green
Green

An upright and long-lived grass growing 90-200 cm tall and forming large tussocks. Its very long and narrow leaf blades (20-70 cm long and 3-10 mm wide) may be flat or somewhat rolled. Its elongated, pyramid-shaped, seed-heads (20-45 cm long and about 3 cm wide) have many short branchesthese seed-head branches are initially held closely to the stem, but as the seed-head opens they become stiffly spreading. Each of these branches bears numerous tiny flower spikelets (1.7-2.2 mm long).

Common names 
Also known as: rat's tail grass, giant rat's tail grass, GRT, Parramatta grass, West Indies smutgrass , whorled dropseed,
Family 
Poaceae
Deciduous 
No
Flowering time 
Spring- Autumn
Native/Exotic 
Exotic
Origin 
Native to sub-Saharan Africa, Madagascar, Mauritius and parts of the the Arabian Peninsula (i.e. Yemen).
Notifiable 
No
State declaration 
Class 2
Council declaration 
Class R – Reduce populations
Known distribution 

This species is widely distributed in the eastern parts of Australia. It is most common in the coastal districts of southern Queensland and northern New South Wales. Also relatively common in the coastal districts of central and northern Queensland and recorded from a few locations 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 90-200 cm tall, that forms large dense tussocks.

Impact and control methods 

This species 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.Along with Sporobolus natalensis, 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.Giant rat's tail grass (Sporobolus pyramidalis) 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. 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.

Stem and leaves 

The flowering stems (i.e. culms) are 2-5 mm thick and somewhat wiry. The leaves are very elongated (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), or have some tiny hairs along their margins, and the leaf blades may be flat or somewhat rolled (i.e. convolute). These leaf blades (20-70 cm long and 3-10 mm wide) are hairless (i.e. glabrous), or have some tiny hairs along their margins, and have pointed tips (i.e. acuminate apices). Where the sheath meets the leaf blade there is a fringe of tiny hairs or a very short membrane (0.2-0.3 mm long) topped with tiny hairs (i.e. the ligule is ciliate or a ciliated membrane).

Flowers and fruits 

The elongated seed-heads are borne at the top of the stems and are initially thin in nature (i.e. spiciform), but become more open and narrowly pyramid-shaped (i.e. pyramidal) as they mature. These seed-heads (20-45 cm long) have numerous stiffly spreading branches (5-10 cm long). Each of these branches bears numerous tiny, densely packed, and elongated (i.e. lanceolate) or oval (i.e. elliptic) flower spikelets almost to its base. The dark green or greyish-green flower spikelets (1.7-2.2 mm long) contain a single tiny flower (i.e. floret) inside two bracts (i.e. glumes). The lower bract (i.e. glume) is 0.3-0.5 mm long and the upper bract (i.e. glume) is 0.5-0.8 mm long (i.e. less than half the length of the flower spikelet). Flowering occurs throughout the year, but mainly during spring, summer and autumn. The tiny seeds (i.e. grains or caryopses) turn yellowish-brown or reddish-brown in colour as they mature. These seeds (0.8-1 mm long and up to 0.5 mm wide) are oblong 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).

Similar species 

Giant rats-tail grass (Sporobolus pyramidalis ) is very similar to other introduced rats-tail grasses (Sporobolus spp.) including another species known as giant rats-tail grass (Sporobolus natalensis), 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 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).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).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).