Palmer amaranth and waterhemp are two troublesome amaranthus species weeds that are resistant to multiple herbicides. They also have unique reproductive features.

Sobering global survey data shows weeds have evolved resistance to 167 herbicides spanning 23 of 26 known sites of action. Now scientists writing in the journal Invasive Plant Science and Management say climate change and elevated levels of carbon dioxide (CO2) may be contributing to the development of herbicide resistance.