Redroot Amaranth refers to the roots that are often red. Amaranthus is from the Greek meaning "not to wither" and refers to the persistent flower spike.
Pigweed (USA) Reflexed Amaranth Red root Redshank is sometimes used locally in Tasmania for this species.
An erect, summer growing, stout, hairy annual herb to 1000 mm high. Many greenish flowers are packed into broad, conical spikes in the leaf axils or at the ends of branches. It often has a rosy red taproot.
Two. Spear shaped. Tip rounded. Hairless. Short merging stalk.
Triangular and hairless with a notched tip.
Alternate. Stipules - Petiole - yes. Blade - Broadly oval or egg shaped, 30-120 mm long. Somewhat undulating near the edges. Often reddish. Obvious veins.
Round, 1000 mm tall, often with a red tinge. Densely hairy. Hairs crisped and short.
Erect, oval, dense, bristly, cylindrical (up to 15mm thick) leafless spikes in the axils of upper leaves and a dense, bristly, leafy panicle with short thick branches at the ends of stems.
Greenish. Bracts - 4-6mm long, longer than perianth, with cusp tips. Perianth - 5 segments, shorter than bracts and the same length or longer than the fruit. Spade shaped with pointed tip that becomes rounded then a broad shallow notch as fruit develops. Ovary - Stamens - 5 Anthers -
Small bladdery bag, 2-3mm long. Nearly as long as the perianth. Opening by a transverse line around the circumference.
Shiny. Flattened. Almost circular in outline with a white ring near the middle. About 1mm wide.
Often rosy red. Taproot.
Spring germinating annual. Flowers December to March. Grows in summer and autumn.
December to March.
Seed Biology and Germination:
Fluctuating temperatures are required to break dormancy.
Population Dynamics and Dispersal:
Origin and History:
North America. Has spread to most temperate regions.
ACT, NSW, SA, TAS, VIC, WA.
Courtesy Australia's Virtual Herbarium.
Often in wet areas.
Often found on fallows.
Weed of summer crops, gardens, vegetables, roadsides, seepage areas, cultivated land and disturbed areas.
Possibly toxic due to nitrate and possibly oxalate. No cases have been reported in Australia.
Cattle and sheep are affected. Sudden death after consuming large quantities of the plant. Infested hay has been implicated in some cases. Kidney trouble in cattle and pigs(perirenal oedema) has been reported from overseas. Symptoms usually appear 5-7 days after exposure. Weakness, trembling, incoordination, knuckling of pastern joints, paralysis of hind limbs, coma and death.
Avoid grazing Redroot Amaranth areas with hungry stock or feeding Amaranth infested hay during the warmer months.