Amaranthus palmeri (Palmer amaranth)
Image credit: Stéphane PaulIdentification tips
Tip #1: the name of the genus amaranthus comes from the Greek "unbeatable", referring to the long-lasting flowers. Palmeri is already named after Edward Palmer, to decorate I like to think that Edward Palmer was a friend of Chuck Norris, and the palmer amaranth today is the Norris of the weeds, the tuff guy of the weeds.
Plant shape
2º Identification tip: it follows growth in a rosette, to make better use of sunlight. A white-colored "V" color spots on the leaves can happen in this species not being an identifying characteristic for this plant.
Leaves
3º Identification tip: the oval shape with thin tips is the common shape of leaves but plants that have been sprayed and survived multiple herbicide applications (especially PPO inhibitors) may exhibit variable leaf formats that may not properly represent the species. But the main characteristic of the leaves that aid in identification is the petiole, which is larger than the blade of the leaf.
could have an spike in the tip of the leaf
Stem
4º Identification tip: the stems do not present hair, this characteristic is essential to identify A. palmeri, therefore, the A. retroflexus and A. hibrydus have hair, so you can easily eliminate these two species if the stem does not have hair, especially when evaluating seedlings.
Flowers
5º Identification tip: the flowers of A. palmeri have two shapes, the feminine ones that are very large and when tightened these spines pike the hand, the male flowers tend to be smaller and not sharp.
Seeds
6º Identification tip: it's almost impossible to identify differences between the seeds of Amaranthus spp. all have the same characteristics. If you feel brave and confident you could try to identify the seeds here
Seedlings - the terror of all
He's not afraid of anything
8º Identification tip: evaluating only leaves and cotyledons are very difficult to identify different seedlings of amaranthus, but the coloring can help, presence of hair and petiole size of the first true leaves.
Extra references:
https://gobotany.nativeplanttrust.org/species/amaranthus/palmeri/
https://aces.nmsu.edu/pubs/_a/A617/welcome.html
https://ipm.missouri.edu/IPCM/2010/7/Weed-of-the-Month-Palmer-Amaranth/