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Weed Identification

roughfruit amaranth



Scientific Name

Amaranthus tuberculatus

Other Common Names:

common waterhemp
tall amaranth
tall waterhemp

Synonyms (former Scientific Names):

Acnida tamariscina
Acnida subnuda
Acnida tuberculata
Acnida concatenata
Amaranthus altissimus
Acnida altissima
Amaranthus ambigens
Amaranthus rudis
Amaranthus tamariscinus


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.

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.

Growth Habit

upright and nonwoody

Thorns or Spines

not present

Approximate Flower Diameter


Dominant Flower Color


Flower Symmetry

radial symmetery

Leaf Hairs

no hairs

Leaf Shape


Leaf Arrangement


Leaf Margin


Leaf Structure


Leaf Stalk

shorter than leaf

Stem Hairs

no hairs

Stem Cross Section

round or oval

Milky Sap

not present

Root Structure


Life Cycle

summer annual


not present

Plant Type