Amaranthus viridis L.
Amaranthus gracilis Desf.
Euxolus
viridis (L.) Moq.
Amaranthaceae
green amaranth, green pigweed, pigweed, Prince of Wales feather, slender amaranth, tropical green amaranth
Native to tropical America.
Green amaranth (Amaranthus viridis) is widely naturalised in Queensland and New South Wales, but is most common in the coastal and sub-coastal districts of these states. It is found throughout south-eastern Queensland, but is most common in the southern parts of the region.
It is also widely naturalised in other parts of Australia (i.e. in Victoria, South Australia, the Northern Territory, Western Australia, Norfolk Island and Christmas Island).
This species is a very common garden weed. It is also a weed of disturbed sites, waste areas, vacant lots, rubbish tips, footpaths, lawns, roadsides, railways, parks, pastures, crops, coastal environs and riparian vegetation.
A short-lived (i.e. annual) herbaceous plant with an upright (i.e. erect) or spreading (i.e. decumbent) habit. It usually grows 40-100 cm tall, but occasionally reaches up to 1.5 m in height.
its tiny fruit (1.5-2 mm long) have a wrinkled surface and each contains a single blackish-brown seed.
The stems are hairless (i.e. glabrous) or sparsely hairy (i.e. puberulent). They are green or reddish-tinged and either round or slightly angled.
The hairless (i.e. glabrous) leaves are alternately arranged along the stems and borne on stalks (i.e. petioles) 7-70 mm long. These leaves (1.5-15 cm long and 1-5.5 cm wide) are egg-shaped in outline (i.e. ovate), elongated (i.e. broadly-lanceolate) or somewhat triangular in shape. They have entire margins and blunt, pointed or notched tips (i.e. obtuse, acute or retuse apices).
Separate male and female flowers are borne on the same plant (i.e. this species is monoecious). The tiny flowers have three 'petals' (i.e. tepals or perianth segments) 1.5-2 mm long. They are borne in branched clusters (5-10 cm long) at the tips of the stems (i.e. in terminal panicles) and also in smaller clusters in the forks of the upper leaves (i.e. in axillary clusters). These flower clusters (i.e. inflorescences) can be greenish, pinkish or reddish-brown in colour. The male flowers, which are mostly found towards the tips of the flower clusters, have three yellow stamens. The female flowers have an ovary topped with tow or three short styles, each of which is tipped with a minute stigma. Flowering occurs throughout the year.
The tiny fruit (i.e. utricles) are 1.5-2 mm long and have a wrinkled surface. Each of these fruit contain a single blackish-brown seed (1-1.5 mm across) with a faintly warty surface texture.
This species reproduces only by seed. These seeds may be dispersed by water and vehicles, in mud, and in contaminated soil or agricultural produce.
This species is not currently declared under any state or local government legislation.
As this species is not a declared plant, its control is not required.
For information on the management of this species see Suburban Weeds (Third Edition), by Kleinschmidt, Holland and Simpson (1996), page 40.
Green amaranth (Amaranthus viridis) may be very easily confused with livid amaranth (Amaranthus blitum). However, these two species can be distinguished from each other by the following differences:
It is also similar to spiny amaranth (Amaranthus spinosus), redshank (Amaranthus hybridus), Powell's amaranth (Amaranthus powellii) and redroot amaranth (Amaranthus retroflexus). However, spiny amaranth (Amaranthus spinosus) can be easily recognized by the presence of two sharp spines (5-12 mm long) at the base of each of its leaves. While redshank (Amaranthus hybridus), Powell's amaranth (Amaranthus powellii) and redroot amaranth (Amaranthus retroflexus ) all have tiny flowers with five 'petals'.
Green amaranth (Amaranthus viridis) is a very common weed of gardens and disturbed sites in the inhabited areas of south-eastern Queensland. It is also relatively common in crops and disturbed natural vegetation (e.g. along tracks in bushland, near camping areas, in revegetation sites, on coastal sand dunes, along cleared rainforest margins, in riparian areas, etc.). However, this species rarely invades undisturbed native vegetation, and is of relatively minor significance as a weed in natural areas.