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Trianthema portulacastrum L. 1753
pronounced: try-an-THEE-muh port-yoo-lah-CASS-trum
(Aizoaceae – the fig-marigold family)
common names: Giant Pigweed, Black Pigweed, (USA) Desert Horsepurslane
Trianthema is derived from the Greek τρι– (tri-), three times, thrice, and ανθεμον (anthemon), a blossom, flower. I have no idea why the ‘three times’ bit is included in the genus name. Portulacastrum is from the Latin portulaca, the Roman name for purslane – botanical Latin for ‘like Portulaca’.
This is a prostrate to decumbent spreading annual broad-leaved herb, up to 15 cm high, and spreading to 1m in diameter. It occurs in wasteland, roadsides, lawns, gardens, cultivated crops, and in paddy fields if the water supply is low. It is native to tropical Africa and Asia and most of the southern states of the USA, but has become naturalized in many other tropical and subtropical countries. In Australia it is alien, and found in Western Australia, the Northern Territory, Queensland and NSW. The specimen photographed was growing on the corner of Granite and Wansfall Streets, Picnic Bay, where land had been disturbed for the laying of sewers. I have also seen it growing up between the paving bricks in the Picnic Bay Mall.
The leaves are opposite, simple (with the pairs of leaves unequal in size), sheathing, petiolate (the petiole expanded into a sheath with 2 small acute lobes, the sheath conjoined with the opposing leaf to form a cup), the petiole 6–20 mm long. The leaf blade is 10–35 mm long by 9–30 mm wide, undissected, elliptic or obovate or orbicular, the base rounded or tapering, the reddish margins entire, the apex acute or apiculate or obtuse. The plants are fleshy and succulent, and the abundant water storage cells in their tissues will sparkle with moisture in direct sunlight.
The inconspicuous flowers are solitary, axillary (almost hidden in the sheath cup), purplish, with 10–25 stamens. The fruit is a capsule, papery or leathery, dehiscent, 2–3.5 mm long, 2–2.5 mm wide. The seed is 1.5–2 mm, kidney-shaped, rough, ridged, reddish brown to black, with an aril. The fruit capsule breaks transversely into an upper lid containing one seed and a lower membranous cup with 3–5 seeds.
Seed dispersal is achieved by several methods: one seed is dispersed in the detached cap of the capsule, which can float, and the other seeds are either dispersed individually from the capsule or remain on the parent plant, reaching the ground to germinate when the parent plant comes to the end of its life.
The larvae of the Spotted Beet Webworm Moth Hymenia perspectalis feed on the plant.
Herbal medicines are produced from the plant, to counteract hyperactivity from amphetamines, to stimulate the cardiovascular system, and to alleviate spasms. The root is powdered and mixed with ginger to form a cathartic to relieve tension and anxiety. It is also a Malian medicinal plant used against various types of illnesses related to the immune response, like joint pains, inflammations, fever, malaria and wounds.
Information about medicinal qualities of plants, or about their use as medicines, is for interest only, and is not intended to be used as a guide for the treatment of medical conditions.
Photographs taken at Picnic Bay 2009, 2010
Page last updated 4th March 2017