Powell's Amaranth

Amaranthus powellii S.Watson

Synonyms - Amaranthus hybridus (misapplied).

Family: Amaranthaceae.

Names:

Amaranthus is from the Greek meaning "not to wither" and refers to the persistent flower spike.
Powell's Amaranth
Other Names:
Amaranthus
Pigweed is sometimes used in Tasmania
Prince of Wales Feather is sometimes used in Tasmania and WA.

Summary:

An erect, stout, annual herb, 700 mm to 2000 mm tall, with more or less horizontal branches from the base and along the length of the stems. Many small, green flowers are packed into long, conical spikes at the ends of branches or from the leaf axils.

Description:

Cotyledons:

Two. The cotyledon is 15 to 20 mm long overall with a merging petiole 5 to 7 mm long, and is hairless. The seedling has both a hypocotyl and epicotyl.

First leaves:

The leaves develop in pairs, the first being 12 to 25 mm long in the blade with a petiole 10 to 20 mm long. They are hairless, but have a few short hairs on the petiole. The first leaves have a distinctive apical notch.

Leaves:

Later leaves have a typical kite shape. The plant does not form a rosette.
Stipules -
Petiole - Hairless, Usually 20-40 mm long on lower stem leaves, but may be up to 100 mm long.
Blade - Egg shaped to oblong. Lower stem leaves are 70 to 90 mm long and are hairless. The leaves developing at the top of the stem are smaller and more elongated. Leaves are usually 25-65 mm long x 9-30 mm wide but may be up to 130 mm x 80 mm. The tip may be acute or rounded.

Stems:

The stems are stout, circular or oval in cross section and solid with shallow longitudinal grooves. Hairless or with sparse, erect, fine hairs particularly on the upper stems. The stem is pale green and frequently reddish in colour though the colour may develop on one side only.

Flower head:

The inflorescences are terminal and axillary, consisting of large numbers of flowers packed tightly into bristly, stout, conical spikes usually with few branches.

Flowers:

The individual flowers are 2 to 3 mm in diameter, sessile and green with five petals. Separate male and female flowers are on the same plant. Female flowers are more numerous than the male flowers.
Bracts - Obvious, green thickened midrib that protrudes as a thick bristle like tip. Narrowly egg shaped. 4-6 mm long.
Ovary -
Perianth - 5 tapering, narrowly oblong to narrowly egg shaped segments that are 2-3 mm long. They are slightly shorter than the fruit.
Stamens -
Anthers - 2 celled.

Fruit:

About 2 mm long. More or less wrinkled. Opens along a transverse line around the middle.

Seeds:

Single. Black. Shiny. Broadly elliptical and 1-1.5 mm long.

Roots:

Taproot.

Key Characters:

Biology:

Life cycle:

Annual. Germination occurs mainly in spring.

Physiology:

Reproduction:

Flowering times:

March in the Perth region.

Seed Biology and Germination:

Vegetative Propagules:

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Origin and History:

North America.

Distribution:

NSW, SA, TAS, VIC.

Courtesy Australia's Virtual Herbarium.

Habitats:

Frequently found around stockyards.

Climate:

Soil:

Plant Associations:

Significance:

Beneficial:

Ornamental.

Detrimental:

It is principally a weed of stock yards, disturbed areas, orchards, hops and home gardens. It is a serious weed of summer crops.

Toxicity:

Not reported as toxic, but other closely related species can be toxic.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Related plants:

Boggabri weed (Amaranthus mitchellii)
Dwarf Amaranth (Amaranthus macrocarpus)
Foxtail (Amaranthus paniculatus)
Green Amaranth (Amaranthus viridis)
Love Lies Bleeding (Amaranthus caudatus)
Native Amaranth (Amaranthus interruptus)
Needleburr (Amaranthus spinosus)
Redroot Amaranth (Amaranthus retroflexus)
Redshank (Amaranthus cruentus)
Rough fruited Amaranth (Amaranthus muricatus)
Slim Amaranth (Amaranthus hybridus)
Spreading Amaranth (Amaranthus deflexus)
South American Amaranth (Amaranthus quitensis)
Tumbleweed (Amaranthus albus) has tiny flowers in the leaf axils.
Amaranthus graecizans.
Batchelor's Buttons (Gomphrena spp.)
Cockscomb (Celosia spp.)

Plants of similar appearance:

In parts of the North-West of Tasmania, a closely allied species Amaranthus retroflexus L. (Redroot, sometimes called 'Redshank' locally) occurs as a weed in vegetable crops. It is very similar in general appearance to Powell's Amaranth but has stems densely covered in woolly hairs. Common names applied to other species of Amaranthus, and occasionally used for the Tasmanian species, include Prince of Wales Feathers and Pigweed. This species has, for a long time, been incorrectly called Amaranthus hybridus L. in Tasmania.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P71. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). p???.

Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). p73. Diagrams.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #68.12.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P94.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.