Weeds in the Fabaceae family

Session on weeds Tuesday night - spent some time on Lotus corniculatus (birdsfoot-trefoil). We were especially enamored with the inflorescence. We removed the papilionaceous petals to expose the stamens exhibiting "free portion of filaments often dilated, sometimes broader than the anther" (Hitchcock), this characteristic distinguishing the genus.
Papilionaceous = butterfly-like, as the irregular corolla of a pea, with a banner petal, two wing petals and two fused keel petals.

We also keyed out Medicago lupulina (black medic), another Fabaceae. Pretty straightforward, those. Having the individual we were working with both in flower and fruit helped quite a bit. Picture of the pods:

Pods of this species are 1-seeded, unarmed (those spiky-looking hairs don't count), reniform, and curved to less than 1 full spiral. Other genus-wide characteristics include trifoliate leaves, pubescent pods and yellow blooms. Fabaceae-wide characteristics include "banner, wings and keel inflorescence. Pea-like pods and often pinnate leaves" (Elpel).