Flowering plant, Riley County, Kansas
(Amaranthus palmeri, AMAPA)
Southern U.S., north to Nebraska.
drawings of plant features
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
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.
Bracts long, 3-7 mm. Tepals 5; first tepal acute, the remaining four
retuse or obtuse, sometimes reflexed. Stigmas 2.
Bracts long, 2.3-5 mm. Tepals 5, first tepal with long midrib extending
0.25-1.4 mm beyond the tepal blade apex.
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.