Alfalfa or weed
This plant is in alfalfa field. Does not look like other alfalfa which has more rounded leaf. This has thin narrow leaf. Alfalfa or weed. What kind of weed? Thanks
Weld County Colorado alfalfa
These leaf pictures are consistent with a variant race of alfalfa plants. No alfalfa seed bank is pure for one plant cultivar, they are always a mix of alfalfa races and cultivars.
The leaves have teeth along the leaf margins only and this is an identifying characteristic of Medicago sativa (Alfalfa). Sweet clovers look a lot like alfalfa but they have small teeth along the entire leaf margin.
Thank you for your question.