As Sara recognized, our mystery seeds from last week were from curly dock, Rumex crispus.
Curly dock is a short-lived perennial that can now be found growing throughout the world. It is thought to be originally from Europe. (Photograph is of related a Rumex). Here in Arizona it can be found in the higher elevations.
In the summer inconspicuous green flowers form on a single, towering stalk.
The plant is easier to recognize when the flower stalk matures and turns a noticeable rusty brown. It stands out against nearby green plants.
The "wings" around the seeds are the calyx (collection of sepals) of the original flowers. The calyx of curly dock has more smoothly rounded margins than some other species, which is an identifying characteristic.
In this video, you can see how the brown stalks stand out. (Note: there may be a pop-up ad).
Have you seen curly dock before? Is it common where you live?