Pictured above is an example of Alfalfa, Medicago sativa. This member of the Pea family (Fabaceae) has been used as a forage crop since 490 BC. It is non-native to the US but it is widely planted to cut for hay and silage. It was most likely first domesticated in Iran and was introduced to the western world by the Greeks.
These plants are perennials and can live from 4 to 20 years. They may produce a taproot that extends up to 49 feet into the soil. This root stores food and its depth helps them resist drought.
In the second image, you can see the pea-like flowers with 5 petals, the awn, the two wings, and the two that form the keel. Their leaves alternate along the stem and are subdivided into 3 leaflets which are toothed along their margins near the tips. Alfalfa resembles native scurfpeas and clovers, but the toothed margins of the leaflets set them apart.
These images were taken in an uncultivated field where there was a mixed stand of wildflowers. The alfalfa was growing wild and seemed to be doing just fine without man’s interference.