red caustic weed

Chamaesyce prostrata

A small, short-lived, herbaceous plant with reddish or purplish creeping stems. Its stems and leaves contain a milky sap. Its paired leaves (3-8 mm long) are dark green to purplish and have entire or finely toothed margins. Its tiny reddish 'flowers' are borne singly or in small clusters in the leaf forks. Its tiny capsules (about 1.5 mm long) are three-sided, with hairs along the angles. These capsules have three compartments, each containing a single pale brown or yellow seed.

Common names 
Also known as: blue weed, creeping spurge, ground fig spurge, ground spurge, groundfig spurge, hairy creeping milkweed, hairy prostrate euphorbia, prostrate mat-spurge, prostrate sandmat, prostrate spurge, red caustic creeper, red caustic weed,
Flowering time 
Native to the USA, Mexico, Central America, the Caribbean and South America.
Council declaration 
SIL – Special Investigation List
Known distribution 

Widely naturalised in south-eastern Queensland, but most common in the Moreton district. Also relatively widespread in other parts of eastern Queensland, naturalised in some parts of eastern New South Wales and the Northern Territory, and present in several offshore island territories (i.e. Lord Howe Island, Norfolk Island, Christmas Island and the Cocos Islands).


A common weed of weed of gardens, footpaths, lawns, parks, nurseries, disturbed sites and waste areas.


A small, short-lived (i.e. annual), herbaceous plant with creeping (i.e. prostate) stems growing up to 20 cm long. Plants may form a dense mat of vegetation over the soil surface.

Impact and control methods 

Red caustic weed (Chamaesyce prostrata) is a relatively common weed of gardens, roadsides, railway lines and disturbed sites in the region. It is rarely a weed of natural vegetation.

Stem and leaves 

Its stems are dark red or purplish in colour and have single row of hairs along their length. The stems and leaves contain a milky sap (i.e. latex). The leaves are paired and borne on very short stalks (i.e. petioles) only 0.5-2 mm long. These leaves (3-8 mm long and 1-5 mm wide) are oblong, oval (i.e. elliptic) or elongated in shape with a rounded tip (i.e. obtuse apex). Their margins are entire or finely toothed (i.e. serrulate), particularly towards their tips. They are dark green, bluish-green, reddish-green or purplish in colour and are usually hairless (i.e. glabrous).

Flowers and fruits 

Tiny male and female flowers are grouped into small cup-like structures (i.e. cyathia). These relatively inconspicuous reddish cyathia are produced singly, or in small clusters, in the leaf forks (i.e. axils). They are borne on stalks (i.e. peduncles) 2-3 mm long and consist of a small cup-like structure (i.e. involucre) about 1 mm long with five minute teeth and four tiny white petal-like appendages (i.e. glands) about 0.2 mm long. They also have several male flowers, each consisting of a single stamen, and a single female flower, consisting of a large stalked ovary. Flowering occurs mainly during summer. The tiny capsules (about 1.5 mm long and 1.4 mm wide) are three-angled with hairs only along the angles. They have three compartments, each containing a single seed. The pale brown or yellow seeds (0.9-1 mm long and about 0.5 mm wide) are four-sided or somewhat egg-shaped (i.e. ovoid) and slightly furrowed.

Reproduction and dispersal 

This species reproduces only by seed, which are dispersed by wind, water, vehicles, in soil and in contaminated agricultural produce.

Similar species 

Red caustic weed (Chamaesyce prostrata) is very similar to spotted spurge (Chamaesyce maculata) and some closely-related native spurges including Chamaesyce dallachyana and Chamaesyce drummondii. These species can be distinguished by the following differences: red caustic weed (Chamaesyce prostrata) has purplish partially hairy stems and its leaves are not spotted. Its three-sided fruit are hairy only on the angles.spotted spurge (Chamaesyce maculata) has green or reddish coloured hairy stems and its leaves often have a purplish or reddish-brown spot in the centre. Its three-sided fruit are softly hairy all over.Chamaesyce dallachyana has green or reddish hairless stems and its leaves are not spotted. Its three-sided fruit are hairless and have fringed bases.Chamaesyce drummondii has green or reddish hairless stems and its leaves are not spotted. Its three-sided fruit are hairless and don't have fringed bases.