The following pigweed species are currently less troublesome in Iowa. Spiny amaranth is a problem weed elsewhere in the United States, but appears to be rare and of limited distribution in Iowa. Tumble pigweed and prostrate pigweed are common in Iowa, but are not important as field weeds.
(Amaranthus spinosus, AMASP)
Distribution: Rare in Iowa, confined mainly to the southern two tiers of counties.
Description: Spiny pigweed is unique in having sharp, vegetative spines throughout the plant at the point where leaves attach to the stem. It also has a unique arrangement of male and female flowering branches, with male flowers found on branches at the top and female flowers on branches near the bottom and middle of the plant.
Notes: Spiny amaranth is distinct due to its spines. Iowa appears to be the northern extension of its range. It is most common in pastures.
(Amaranthus albus, AMAAL)
Distribution: Tumble pigweed is found in all counties of Iowa.
Description: Tumble pigweed is a small plant, about three feet high at maturity. Its flowers are found in small, inconspicuous clusters throughout the plant attached between the leaves and stems.
Notes: Tumble pigweed is common across the entire United States. In Iowa it seems to be confined mainly to construction areas and is not currently an important field weed.
(Amaranthus blitoides, AMABL)
Distribution: Prostrate pigweed is found in all counties of Iowa.
Description: Prostrate pigweed is a low-lying, spreading, mat-like plant, rarely growing more than a few inches off the ground. Like tumble pigweed, its flowers are found in small, inconspicuous clusters throughout the plant attached between the leaves and stems.
Notes: Although prostrate pigweed is common in the state, it seems to be confined to sidewalk cracks and waste ground. It is not a major agricultural weed.