Weeds of Australia - Fact Sheet

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

Scientific Name

Euphorbia heterophylla L.

Synonyms

Euphorbia cyathophora Murr. (misapplied)
Euphorbia geniculata Ortega
Euphorbia prunifolia Jacq.
Poinsettia geniculata (Ortega) Klotzsch & Garcke
Poinsettia heterophylla (L.) Klotzsch & Garcke

Family

Euphorbiaceae

Common Names

desert spurge, fire plant, Japanese poinsettia, Mexican fire plant, Mexican fireplant, milk weed, milkweed, painted euphorbia, painted leaf, painted spurge, paintedleaf, summer poinsettia, various leaved euphorbia, wild poinsettia, wild spurge, yellow spurge

Origin

Native to tropical America (i.e. from southern USA, through Central America and the Caribbean, south to Argentina).

Naturalised Distribution

Widely naturalised in the northern regions of Australia. This species is most common in the coastal districts of Queensland, in the coastal and sub-coastal districts of the Northern Territory, and in the northernmost parts of Western Australia. It is occasionally also naturalised in other parts of these states, present in south-eastern South Australia, and naturalised on Christmas Island.

Habitat

A weed of crops, orchards, roadsides, gardens, waste areas and disturbed sites in tropical, sub-tropical, semi-arid and occasionally also temperate regions. Also commonly growing in urban bushland and along creekbanks (i.e. in riparian vegetation).

Habit

A short-lived (i.e. annual) plant with an upright (i.e. erect) and branched main stem usually growing 20-80 cm tall, but occasionally reaching up to 2 m in height.

Distinguishing Features

• a short-lived upright herbaceous plant usually growing 20-80 cm tall.
  
  
• all parts of the plant have a milky sap.
  
  
• its leaves are generally green, but those just below the flower clusters may occasionally have paler whitish patches or splotches of purplish-green towards their bases, but these are not very distinct.
  
  
• its greenish-yellow clusters of 'flowers' are borne at the tips of the branches.
  
  

• its small three-lobed capsules (3-4 mm long and 5-6 mm across) each contain three seeds.

Seedling

The two seed leaves (i.e. cotyledons) are oval in shape (i.e. elliptic) and are borne on stalks (i.e. petioles) about 5 mm long. They are about 22 mm long and 8 mm wide when fully grown. The first true leaves are paired (i.e. oppositely arranged) and are more egg-shaped in outline (i.e. ovate).

Stems and Leaves

The upright (i.e. erect) main stems are 3-8 mm thick and side (i.e. lateral) branches are formed in the leaf forks (i.e. axils). These stems are either hairless (i.e. glabrous) or somewhat hairy (i.e. pilose). The stems and leaves exude a caustic milky sap (i.e. latex) when broken or damaged.

The variable leaves (2-12 cm long and 0.8-5 cm wide) are generally green in colour and borne on stalks (i.e. petioles) 5-40 mm long. They are usually oval (i.e. elliptic), egg-shaped in outline (i.e. ovate) or elongated (i.e. lanceolate) in shape with a pointed tip (i.e. acute apex). These leaves are also either entirely hairless (i.e. glabrous) or somewhat hairy (i.e. pilose) with margins that are entire to very finely toothed (i.e. serrulate). Leaves tend to be oppositely arranged on the lower parts of the stem, alternately arranged along most of the stem, and then oppositely arranged again just below the flower clusters. The leaves just below the flower clusters (i.e. the floral leaves) may occasionally have paler whitish patches or splotches of purplish-green towards their bases, but these are not very distinct.

Flowers and Fruit

The inconspicuous 'flowers' (i.e. cyathia) are actually tiny cup-like structures (i.e. involucres) each containing several tiny male flowers and one female flower. The male flowers are reduced to stamens and the female flower consists of a very large stalked ovary topped with a stigma. These 'flowers' (i.e. cyathia) are borne in dense clusters at the tips of the branches (i.e. in dense terminal cymes), usually with several leaves clustered directly below them. The 'flowers' (i.e. cyathia) are greenish or yellowish in colour and each one is borne on a separate stalk (i.e. peduncle). The cup-like structures (i.e. involucres) are about 2-2.5 mm long and on each of these there is also a smaller rounded cup-like projection (i.e. floral nectary or gland).

The three-lobed capsules (3-4 mm long and 5-6 mm across) are hairless (i.e. glabrous) and each contains three seeds. The seeds (2.5-3 mm long) are egg-shaped (i.e. ovoid), either brownish or mottled grey in colour, and have rough (i.e. coarsely tuberculate) surfaces.

Reproduction and Dispersal

This species reproduces by seed, which may be spread in contaminated agricultural produce, by water, and in mud attached to vehicles and animals.

Environmental Impact

Milkweed (Euphorbia heterophylla) is regarded as an environmental weed in Queensland and as an emerging or potential environmental weed in the Northern Territory. It is ranked among the top 200 environmental weeds south-eastern Queensland, where it is becoming common along waterways, in urban bushland and in disturbed sites.

Milkweed (Euphorbia heterophylla) is also a common weed of streambanks in northern Queensland and is ranked among the top 25 environmental weeds in the Wet Tropics bioregion. It is one of a number of weeds that have been identified as having the potential to cause significant environmental damage in the wet tropics region, though it currently only has localised impacts on biodiversity.

Other Impacts

Milkweed (Euphorbia heterophylla ) is also an important weed of summer crops in northern Australia. It is regarded as a major weed of crops in coastal central Queensland, a moderately important crop weed in northern Queensland, and a minor weed of crops in the Northern Territory.

This species is also poisonous to livestock and humans, and its milky sap (i.e. latex) is highly irritating when it comes into contact with the skin or when it is accidentally rubbed into the eyes.

Legislation

Not declared or considered noxious by any state government authorities.

Similar Species

Painted spurge (Euphorbia cyathophora) and poinsettia (Euphorbia pulcherrima) are both very similar to milkweed (Euphorbia heterophylla). These three species can be distinguished by the following differences:

• milkweed (Euphorbia heterophylla) is a relatively small herb (usually 20-80 cm tall) with leaves that are elongated (i.e. lanceolate) or egg-shaped in outline (i.e ovate). The cluster of leaves directly beneath its flowers are usually entirely green in colour, but their bases may be a slightly different colour.
  
  
• painted spurge (Euphorbia cyathophora) is a relatively small herb (usually less than 1 m tall) with leaves that are sometimes distinctively lobed or fiddle-shaped (i.e. pandurate). The cluster of leaves directly beneath its flowers usually have very distinct bright reddish-pink or orange coloured bases.
  
  
• poinsettia (Euphorbia pulcherrima) is a relatively large shrubby plant (usually 1-3 m tall) with woody stems and leaves that are usually variously toothed or lobed. The cluster of leaves directly beneath its flowers are usually entirely bright red or reddish-green in colour (or occasionally white).