Flowering plant, Riley County, Kansas


Seedlings


Female seedhead


Male flowers

Palmer Amaranth
(Amaranthus palmeri, AMAPA)

U.S. Distribution: Southern U.S., north to Nebraska.

Line drawings of plant features

Descriptions
Seedlings
: Seed leaves are long and wide. First true leaves are egg-shaped, later leaves becoming diamond-shaped. Seedlings are very smooth and hairless. Leaves may have a white or red V-shaped mark during early stages of development.

Adults: Palmer amaranth is an extremely vigorous, tall plant. Stems and leaves vary from green to pink. The leaves are diamond-shaped and have long leaf stalks. Leaf tips have a fine, short hair extending from the midrib beyond the leaf blade. Stems and leaves are hairless and smooth. The seedhead is very long, thick, and extremely prickly due to the very long bracts.

Technical Characters
Pistillate flowers
: Bracts long, 3-7 mm. Tepals 5; first tepal acute, the remaining four retuse or obtuse, sometimes reflexed. Stigmas 2.

Staminate flowers: Bracts long, 2.3-5 mm. Tepals 5, first tepal with long midrib extending 0.25-1.4 mm beyond the tepal blade apex.

Management
This species is not currently established in Iowa. However, it has been rapidly extending its range northward into southern Missouri, Nebraska, and Illinois, and a few samples are known from southwestern Iowa. Palmer amaranth can be ALS herbicide resistant. It grows vigorously and post-emergence herbicides like the diphenylethers may not be effective. This species has an extended germination time and should be managed similarly to common waterhemp. Contact the ISU Extension Agronomy Office, 2104 Agronomy Hall, Ames IA 50011, telephone (515) 294-1923, Fax (515) 294-9985 if you believe you have found this species in your fields.