Weeds of Australia - Fact Sheet

Top Scientific Name Synonyms Family Common Names Origin Cultivation Naturalised Distribution Habitat Habit Distinguishing Features Stems and Leaves Flowers and Fruit Reproduction and Dispersal Environmental Impact Legislation Similar Species

Scientific Name

Aerva javanica (Burm. f.) Juss. ex Schult.

Synonyms

Aerva persica (Burm. f.) Merr.
Aerva tomentosa Forssk.
Iresine javanica Burm. f.
Iresine persica Burm. f.

Family

Amaranthaceae

Common Names

aerva, Java aerva, kapok bush, kapokbush, pillow bush, snow bush

Origin

This species is widespread in the drier parts of tropical and sub-tropical Africa and Asia. It is found throughout much of mainland Africa and is also present on the Cape Verde islands and in Madagscar. Its natural range also includes the Arabian Peninsula  and areas further eastwards in southern Asia and the Indian sub-continent.

Cultivation

This species was deliberately introduced as a fodder plant for drier regions, and for the revegetation of degraded rangeland pastures.

Naturalised Distribution

This species is widely naturalised in the drier regions of northern Australia. It is most common and widespread in the northern and north-western parts of Western Australia (particularly in the Kimberley and Pilbara regions). In the Northern Territory it is relatively common in north-western areas and is also scattered throughout the remainder of the territory. In Queensland it is relatively common in the inland parts of the north of the state with isolated populations in some other regions.

Occasional naturalised populations have also been reported in north-western New South Wales and in northern South Australia.

Habitat

In its native range, as in Australia, it is mostly found growing on sandy or calcareous soils in semi-arid and arid regions (in inland areas and also near the sea).

Habit

A long-lived (i.e. perennial), upright (i.e. erect), herbaceous plant or small and slightly woody shrub. It usually grows 30-100 cm tall, but occasionally reaches up to 1.6 m in height.

Distinguishing Features

• a long-lived upright herbaceous plant or small shrub growing 30-160 cm tall.
  
  
• its stems and leaves, particularly their undersides, are densely covered in whitish woolly hairs.
  
  
• its numerous whitish flowers are borne in elongated clusters at the tips of the branches.
  
  
• separate male and female flowers are borne on separate plants.
  
  
• its tiny capsule-like fruit (1-1.5 mm long) each contain a single shiny black or dark brown seed.

Stems and Leaves

The upright (i.e. erect) stems are branched from the base of the plant and can sometimes be fairly woody in nature. These stems are rounded in cross-section (i.e. terete) with slight ridges running lengthwise (i.e. they are striated). They are densely covered in whitish or occasionally yellowish hairs (i.e. tomentose or pannose).

The simple leaves (2-7 cm long) are alternately arranged along the stems and are quite variable in shape. They can range from being long and narrow (i.e. linear) to being almost round (i.e. sub-orbicular). Their upper surfaces are thinly covered in whitish hairs and are greenish in colour, while their undersides are more densely covered in these hairs and have a whitish appearance (i.e. they are tomentose). These leaves are usually stalkless (i.e. sessile), but they are sometimes borne on a short stalk (i.e. petiole) less than 2 cm long.

Flowers and Fruit

The whitish flowers are borne in elongated clusters at the tips of the branches (i.e. in terminal spikes). These clusters (up to 10 cm long and 10 mm wide) may be dense and continuous or somewhat interupted, especially in their lower parts. Separate male and female flowers are borne on separate plants (i.e. this species is dioecious). The male flower clusters are often more slender (i.e. only up to 5 mm wide) than the female flower clusters. Both types of flowers are stalkless (i.e. sessile) and have three tiny bracts (0.75-2.25 mm long) underneath them. These bracts are narrow or egg-shaped in outline (i.e. lanceolate to ovate) and are at least partly covered in a dense layer of white woolly hairs (i.e. they are partly tomentose). They can have rounded or pointed tips (i.e. obtuse or acute apices) and remain on the plant (i.e. they are persistent) after the 'petals' have fallen. Both types of flowers also have five small 'petals' (i.e. perianth segments or tepals). These 'petals' are relatively broad (i.e. obovate), have very hairy outsides, and two of them are slightly larger than the other three. The 'petals' on the female flowers are larger than those on the male flowers (i.e. 2-3 mm long on female flowers and 1.5-2.25 mm long on male flowers). Female flowers also have a small ovary and a slender style with two very elongated (i.e. filiform) stigmas at its tip, while male flowers have five delicate yellowish-coloured stamens. Flowering occurs throughout most of the year, generally after significant rainfall events.

The very small (1-1.5 mm long) capsule-like fruit (i.e. utricles) are rounded in shape, but somewhat flattened (i.e. compressed). Each fruit contains a single dark brown to black coloured seed. These seeds are round or slightly flattened (0.9-1.25 mm), shiny in appearance, and generally smooth in texture. However, they can sometimes have a very faint surface pattern (i.e. they are sometimes faintly reticulate).

Reproduction and Dispersal

This species reproduces by seed, which are only produced on female plants. The small fruit are probably dispersed by animals and wind. They may also be spread by vehicles and in soil, as infestations often first appear along roadsides and near minesites.

Environmental Impact

Though kapok bush (Aerva javanica) is relatively widespread across northern Australia, it has only recently come to be regarded as a serious environmental weed. There are conflicting opinions to its invasiveness and impact and it is currently only regarded as a significant problem in Western Australia. This is probably largely because it is a relatively useful fodder species in drier rangeland areas and has been deliberately cultivated in some instances.

In Western Australia, this plant was recently rated as being highly invasive, and having a high level of impact, in the state's Environmental Weed Strategy. In fact, it was one of only 34 invasive plant species that were given the highest invasiveness rating in Western Australia. However, in the Northern Territory, kapok bush (Aerva javanica) is generally not considered a threatening weed species, even though it already occurs in conservation areas (e.g. in the Gregory National Park). Other information sources also state that it is not known to have an impact on plant biodiversity.

Recent reports from Western Australia indicate that this species is spreading from rangelands and becoming more prominent in parks and nature reserves and on minesites (both on the mainland and on offshore islands). For example, it is a weed in Geikie Gorge National Park in the far north Kimberley Region of Western Australia, is subject to a control operation in Millstream National Park in the Pilbara Region further south, and is a weed species of particular concern on the peninsula in the Cape Range National Park south of Exmouth. It is listed as a notable environmental weed species on the islands in the Dampier Archipelago Nature Reserve, off the coast of Dampier, and small scale infestations have also appeared on Barrow Island. Kapok bush (Aerva javanica) is also commonly associated with disturbed areas sush as ports, industrial areas and minesites in this part of Western Australia (e.g. at Cape Lambert, around West Intercourse Island and at Cape Preston). These sites are often located near parks and reserves and spread of this species from such sites is a growing concern.

Legislation

This species is not declared or considered noxious by any state or territory government in Australia.

Similar Species

Kapok bush (Aerva javanica) is very similar to some of the large group of native plants known as bottlewashers or mullamullas(i.e. Ptilotus spp.) at a distance, including the very common and widespread species known as green mullamulla (Ptilotus polystachyus). However, these native species generally have broader inflorescences and are not densely covered in white woolly hairs. The fruit of these species also contain more than one seed.

There are a also a couple of introduced weeds in eastern Australia that can be confused with kapok bush (Aerva javanica). These two plants are called cottontails (Froelichia floridana) and slender cottontails (Froelichia gracilis). However, they can be distinguished by their paired (i.e. oppositely arranged) leaves and slightly larger fruit (i.e. 2.5-5 mm long).