Once a foxtail plant becomes established and several leaves are emerged, it becomes easier to ID the several species. Focus on the collar region, the hairy ligule, and the leaves:
Yellow & knotroot foxtail:
The picture above, left, shows a hairy leaf surface of giant foxtail. The one on the
right has no hairs. Originally this picture was taken to show green foxtail hairless
leaves. 95% of the time the lack of hairs will indicate green foxtail, but 5% (at least in
areas of Iowa that I have observed) of the time you will have a hairless giant foxtail,
often called the (jolly) green giant foxtail. Just in case you haven't got the message
from this about weed (and foxtail) biodiversity, some green foxtail seedheads are very
large, the biotypes often are called green giant foxtail.
Below you can see a green foxtail biotype known as purple robust foxtail. These plants came from a field near Monroe, Michigan, home of General George Custer as well as the shock absorber company.
The ligule and collar region:
These line drawings indicate that green foxtail stems (culms) can have variable degrees of hairiness. Oh that foxtail biodiversity.
Yellow & knotroot foxtails:
Some giant foxtail variants can spread its stems along the ground, called a decumbent habit, to capture more sunlight by lateral spread:
Foxtail species, and variants, possess different abilities to tiller, to form several lateral stems from branching nodes. Green foxtail probably has the greatest ability to tiller, giant maybe the least. All foxtails can tiller to some degree if enough extra resources for growth are available. This ability to tiller when more resources are available is an example of "plasticity" or "plastic growth", and important weedy adaptation to the agroecosystem. Green foxtail with lots of tillers:
The tillering green foxtail above also shows us it fibrous root system, as in the picture below:
Foxtail Species-Group | Leaves,
Stems & Roots
Flowers & Seedheads | Foxtail Adaptation