Scientific NameAmaranthus tuberculatus
Other Common Names:
Synonyms (former Scientific Names):
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 lack hairs, and have conspicuous veins. The petiole is usually half the blade length. Blades are oblong or narrow and much longer than wide.
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.
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.
Wet areas, such as margins of rivers, ponds, marshes, lakes, and creeks, and disturbed habitats, such as agricultural fields, roadsides, and railroads.
upright and nonwoody
Thorns or Spines
Approximate Flower Diameter
Dominant Flower Color
shorter than leaf
Stem Cross Section
round or oval