Latin name

Amaranthus spinosus L.

Family

Amaranthaceae

Common name(s)

Spiny amaranth, spiny pigweed, needle burr

Synonym(s)

A. caracasanus Kunth

Geographical distribution

Asia: Japan and China (Taiwan).

South and Southeast Asia: Bangladesh, Indonesia, India, Lao PDR, Nepal, Philippines, Sri Lanka, Thailand, and Vietnam.

Rest of the world: Argentina, Australia, Bolivia, Brazil, Colombia, Costa Rica, Cuba, Ecuador, El Salvador, Ethiopia, Fiji, Guatemala, Honduras, Jamaica, Madagascar, Mauritius, Mexico, Nicaragua, Peru, Puerto Rico, United States, and Venezuela.

Morphology

A stout, erect, annual herb, 40—100—cm—tall.

Stem: reddish/pink color, without hairs, fleshy, branched, and longitudinally grooved. Pairs of slender, sharp-pointed and 6—10—mm—long spines are located at axils of lower leaves and branches.

Leaf: simple, ovate to broadly lance-shaped, 3—12—cm—long and 2—5—cm—wide, alternate, with 2—8—cm—long petiole, hair-like points often found at the indented tip.

Inflorescence: composed of terminal and axillary spikes of closely packed clusters of small purplish or green flowers about 1—mm—long; upper flowers male, lower ones female. Terminal spikes 7—15—cm—long, with paired spines at base of flower clusters; axillary spikes shorter and lack paired spines.

Fruit: single-seeded capsule; seed shiny and black, lens-shaped and 0.5—mm in diameter. Amarantus viridis L. similar but without spines.

Biology and ecology

Prefers rich and moist soils; found in upland field crops, plantation crops, gardens, pastures, and along roadsides.

Does not flower in shade or cool temperatures; propagated by seeds; record of 117,000 seeds produced per plant.

Agricultural importance

In Thailand, used as a food plant; leaves are consumed as spinach and seeds as grains; whole plant is used to cure wounds. Host of nematodes and tobacco mosaic and groundnut rosette viruses.

Management

Cultural control: hoeing and hand weeding.

Chemical control: butachlor as preemergence and propanil or 2,4-D as postemergence treatments are reported for control of A. spinosus.

Selected references

Galinato MI, Moody K, Piggin CM. 1999. Upland rice weeds of South and Southeast Asia. Manila (Philippines): International Rice Research Institute. 156 p.

Holm LG, Plucknett DL, Pancho JV, Herberger JP. 1977. The world's worst weeds. Honolulu, Hawaii (USA): The University Press of Hawaii. 609 p.

Merrill ED. 1976. A flora of Manila. Manila (Philippines): Department of the Interior, Bureau of Science. 491 p.

Moody K. 1989. Weeds reported in rice in South and Southeast Asia. Manila (Philippines): International Rice Research Institute. 442 p.

Soerjani M, Kostermans AJGH, Tjitrosoepomo G. 1987. Weeds of rice in Indonesia. Jakarta (Indonesia): Balai Pustaka. 716 p.

W3 TROPICOS at http://mobot.mobot.org/Pick/Search/pick.html.

Contributors

JLA Catindig, RT Lubigan, and DE Johnson