Weed Seed: Amaranthus tuberculatus (Tall water-hemp)

Family

Amaranthaceae

Common Name

Tall water-hemp

Regulation

Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs in MB, ON, QC (Brouillet et al. 2016Footnote 1, Darbyshire 2003Footnote 2).

Worldwide: Native to eastern North America (USDA-ARS 2016Footnote 3) and introduced into Asia (Israel and Jordan), the western United States and Europe (CABI 2016Footnote 4).

Duration of life cycle

Annual

Seed or fruit type

Seed

Identification features

Size

  • Seed diameter: 0.8 - 1.3 mm

Shape

  • Seed is oval or ovate

Surface Texture

  • Seed is glossy, smooth

Colour

  • Dark reddish brown

Other Features

  • Hilum is near the top of the seed in a notch.
  • Seeds may have a persistent funiculus at the hilum.
  • The rim around the outside of the seed, common in Amaranthus spp. is diminished or lacking in this species.

Habitat and Crop Association

Cultivated fields, wet areas, including the margins of ponds, rivers and ditches, roadsides, and disturbed areas (Darbyshire 2003Footnote 2, FNA 1993+Footnote 5). A dominant weed of soybean and corn fields in the United States (Costea et al. 2005Footnote 6).

General Information

Tall water-hemp produces 35,000-1,200,000 seeds per plant and forms persistent seed banks under cultivation (Costea et al. 2005Footnote 6).

This species prefers warm, moderately moist, nitrogen-rich sites in full sunlight (Costea et al. 2005Footnote 6). Considering that both seed and fruits float and the species prefers to grow near water, (Costea et al. 2005Footnote 6) suggest that dispersal by water may be significant.

Similar species

Redroot pigweed (Amaranthus retroflexus)

  • Redroot pigweed seed has a similar lenticular shape, notched hilum and glossy surface as tall water-hemp.
  • Redroot pigweed seed is larger by up to 0.5 mm, has a pronounced rim, and is black.
  • Tall water-hemp seeds do not have a rim and are reddish-brown.

Photos

Tall water-hemp (Amaranthus tuberculatus) seeds and capsule
Tall water-hemp (Amaranthus tuberculatus) seeds and capsule
Tall water-hemp (Amaranthus tuberculatus) seed
Tall water-hemp (Amaranthus tuberculatus) seed
Tall water-hemp (Amaranthus tuberculatus) seed, hilum view
Tall water-hemp (Amaranthus tuberculatus) seed; hilum view

Similar species

Similar species: Red-root pigweed (Amaranthus retroflexus) seeds
Similar species: Red-root pigweed (Amaranthus retroflexus) seeds
Similar species: Red-root pigweed (Amaranthus retroflexus) seed
Similar species: Red-root pigweed (Amaranthus retroflexus) seed
Similar species: Red-root pigweed (Amaranthus retroflexus) seed
Similar species: Red-root pigweed (Amaranthus retroflexus) seed
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