You might recognize these yellow flowers, or you might not. You don't usually see them in cut form, in a vase.
You might think "mustard" if you are from California. Or "canola" if you are from Canada — "colza" in France. Or "rape" (photo of flower) — a.k.a. "oilseed rape" (Wiki article). But it's none of those.
In Touraine in April, there are wide fields of similar yellow flowers all around the countryside. In fact, mustard, rape, and the plant in question are all members of the cabbage family.
These flowers (and leaves) grew in our vegetable garden. They survived the winter. I pulled the plants out yesterday and spent the day trimming, cleaning, and cooking the leaves.
After you've looked at the other two pictures in this post, you might have a better idea. And knowing my Southern background will help...