Fire-on-the-mountain (Euphorbia cyathophora)

Origin:

Fire-on-the-mountain (Euphorbia cyathophora) Weed.

Native to tropical North America (i.e. the USA and eastern Mexico) and possibly also Central America (i.e. Belize, Costa Rica, Guatemala, Honduras and Panama), the Caribbean and South America (i.e. Bolivia, Colombia, Ecuador, Argentina and Chile).

Naturalised Distribution:

This species has a widespread, but scattered, distribution throughout much of Australia. It is most common in the coastal districts of Queensland and northern New South Wales, scattered in the Northern Territory and in the northern and western parts of Western Australia, and present in the coastal districts of central New South Wales. Also naturalised on several offshore islands (i.e. Lord Howe Island, Christmas Island, Norfolk Island, the Cocos Islands and the Coral Sea Islands) and sparingly naturalised on the Eyre Peninsula in South Australia.

Naturalised in many other parts of the world, including on numerous Pacific islands (e.g. Fiji, French Polynesia, Guam, Hawaii, Kiribati, the Marshall Islands, Nauru, New Caledonia, Niue, Palau and Wake Island).

Cultivation:

Painted spurge (Euphorbia cyathophora) is widely cultivated, particularly in the warmer parts of Australia, for its attractive reddish-coloured floral leaves.

Habitat:

This species is a weed of disturbed sites, waste areas, roadsides, creek banks (i.e. riparian areas) and plantation crops (e.g. sugar cane and pineapples) in tropical, sub-tropical and warmer temperate environments. However, it is most abundant as a weed of coastal environs and offshore islands.

Distinguishing Features:

  • A short-lived upright herbaceous plant usually less than 1 m tall.
  • Its stems and leaves have a milky sap.
  • Its leaves are often fiddle-shaped and are usually alternately arranged along the stems.
  • The leaves just below the ‘flowers’ have reddish-pink coloured bases (i.e. they appear to be ‘painted’) and can easily be mistaken for large petals at a distance.
  • Its inconspicuous greenish-coloured ‘flowers’ are borne at the tips of the branches.

    Fire-on-the-mountain (Euphorbia cyathophora) Distribution in North America shown in green.

Habit:

A short-lived (i.e. annual) herbaceous plant with an upright (i.e. erect) habit. It usually only grows to approximately 70-90 cm in height.

Stems and Leaves:

The upright (i.e. erect) stems are 3-5 mm thick and their side-branches, when present, are often produced in pairs. Stems and branches are green in colour and mostly hairless (i.e. glabrous). The stems and leaves also exude a caustic milky sap (i.e. latex) when broken or damaged.

The leaves are oppositely arranged towards the base of the plant, alternately arranged along most of the stem, and are then oppositely arranged again on the uppermost parts of the stems and branches (i.e. where the flowers are produced). These leaves (2-10 cm long and 1-4 cm wide) are borne on stalks (i.e. petioles) 4-12 mm long and the shape of the leaf blade is quite variable. It ranges from fiddle-shaped (i.e. pandurate) or lobed through to oval (i.e. elliptic) or egg-shaped in outline (i.e. obovate). The upper surface of these leaves is hairless (i.e. glabrous) while the under surface usually has a few close-lying (i.e. appressed) hairs. The leaves at the tips of the branches (i.e. those just below the flowers) have reddish-pink coloured bases and can appear to be large flower petals at a distance.

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 clustered at the tips of the branches and are yellowish-green in colour. Each ‘flower’ (i.e. cyathium) is borne on a

Close up of the Fire-on-the-mountain (Euphorbia cyathophora) Weed.

separate stalk (i.e. peduncle) and the tiny cup-like structures (i.e. involucres) are about 2-2.5 mm long. They usually also have one or two kidney-shaped yellowish structures that contain nectar (i.e. floral nectaries).

The fruit is a three-lobed capsule (3-4 mm long and 5-6 mm wide) with three inner compartments, each containing a single seed. Seeds are egg-shaped (i.e. ovoid) and dark brown in colour (2-3 mm long and about 1.5 mm wide).

Reproduction and Dispersal:

Painted spurge (Euphorbia cyathophora) reproduces by seed. The capsules open explosively when mature, expelling the seeds short distances. They may also be spread by water movement and is dumped garden waste.

Impacts:

Painted spurge (Euphorbia cyathophora) is regarded as an environmental weed in Queensland and New South Wales. It is ranked among the top 200 environmental weeds in south-eastern Queensland and north-eastern New South Wales, and appears on numerous local environmental weed lists in these regions.

This species prefers sandy soils, particularly in disturbed sites. It is of most concern as a weed of hind-dune areas on beaches and is also relatively common in coastal and sub-coastal riparian zones. In Queensland painted spurge (Euphorbia cyathophora) is most prevalent in the south-eastern parts of the state, but is also a weed of beaches and offshore islands in the north (e.g. in Townsville City, in Sarina Shire, on Heron Island and on Green Island).

In New South Wales painted spurge (Euphorbia cyathophora) is mainly a problem in coastal sandy sites north of Coffs Harbour on the mid north coast. In Western Australia it is an occasional weed in the northern parts of the state (e.g. at Derby and Broome), has been recorded in suburban Perth, and is also present on offshore islands (i.e. on Koolan Island).

Other Impacts:

This species is poisonous to humans. Its stems contain a milky sap (i.e. latex) that is highly irritating when it comes into contact with the skin or when it is accidentally rubbed into the eyes.

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