Scientific Name: Amaranthus tuberculatus

Common Name: roughfruit amaranth

Other Common Names: common waterhemp, tall amaranth, tall waterhemp

Synonyms: Acnida altissima, Acnida concatenata, Acnida subnuda, Acnida tamariscina, Acnida tuberculata, Amaranthus altissimus, Amaranthus ambigens, Amaranthus rudis, Amaranthus tamariscinus

Habit: Plants germinate in spring and quickly grow during the summer months. Flowering occurs in mid summer until frost and a single plant may produce thousands of tiny seed. Stems are erect to sometimes ascending, and usually grow to 3-7 feet in height.

Leaves: Leaves lack hairs, and have conspicuous veins. The petiole is usually half the blade length. Blades are oblong or narrow and much longer than wide.

Identifying Characteristics: Tall waterhemp has no hair on the stem or leaves, while most other pigweeds have some hair. This characteristic is especially evident when inspecting the newest emerging leaf on young plants. If this newest leaf is hairless, the plant is most likely tall waterhemp or Palmer amaranth. Palmer amaranth leaves, however, are short and broad with petioles that area usually at least as long as the leaf.

Flower Seed Head: Flowers are inconspicuous and produced in a terminal inflorescence containing branched spikes with numerous green, brown, or reddish flowers. Some plants produce male flowers that will have yellow stamens and lack seed and other plants produce female flowers that are usually green, often have white stigmas, and will typically expel shiny brown to black seed when beat across the palm.

Seed Fruit: Seeds are dark reddish brown to dark brown, 0.7-1 mm in diameter, and shiny. Each seed is enclosed in a papery sack (utricle) that splits in half easily dispelling the shiny seed.

Where Found: Wet areas, such as margins of rivers, ponds, marshes, lakes, and creeks, and disturbed habitats, such as agricultural fields, roadsides, and railroads.

  • Life cycle: summer annual

  • Milky sap: Not Present

  • Plant type: Herb

  • Thorns: Not Present

  • Plant family: Amaranthaceae

  • Leaf arrangement: alternate

  • Leaf shape: oval

  • Ochrea: Not Present

  • Leaf margin: entire

  • Stem hairs: no hairs

  • Flower color: green

  • Growth habit: upright and nonwoody

  • Stem: round or oval

  • Leaf structure: simple

  • Leaf hairs: no hairs

  • Flower diameter: pencil

  • Flower symmetry: radial symetery

  • Root structure: taproot

  • Leaf stalk: shorter than leaf