Looks like some type of cocclebur.

Bur clover

Not familiar with the plant but, compare to Medicago arabica.

(Thanks, Flora! I looked up M. orbicularis after you answered that in a post the other day and saw this one and remembered it.)

FataMorgana

Not sure about the species, but agree with the Medicago part.

Thank you so much for your responses!

medicago polymorpha

We have something similar, but the spiny pods are much larger. Some kind of wild cucumber I'm told, but NOT edible. We round ours up when they first appear in spring, and they are no longer the pest they were when we first moved here. We are on the edge of a wild ravine, and the stuff is uncontrolled there, so seeds blow here. It's an endless battle. Good luck getting rid of it. You can kill it with boiling water on it's roots, but again, that is a pain to do!

Hi all, thanks again for the responses! I did some research on the plant type based on this info, and sounds like there is not much to do that would be effective: pulling them (they are basically the whole yard in some areas, so I would be pulling out everything!), dousing them with vinegar/weed killer (again, would require killing everything!), or putting on corn gluten meal (too late in the season since they're already grown). Given that the pods are already formed, is there any damage control I can do? For example, somehow catching them by running some kind of special cloth across the lawn, if that exists, or similar? I'm willing to try anything!

If it's an annual, mowing should greatly reduce the amount of seedlings for next year. You'd want to use the bag on the mower so the seeds aren't re-deposited on the ground, mow as low as possible. With any annual plant, preventing its' seeds from falling should interrupt the cycle and help you get control. In order for it to show up every year, an annual plant has to make & drop seeds. The original plants don't live into the next year.

Thank you! It seems that this plant grows extremely low to the ground, basically creeping along the ground -- mowing helps reduce the number of seeds/burrs for sure, but there are still a massive quantity even though our lawn is mowed as low as possible once per week. Is there anything else we can do?

Cut with rose pruners to within a few inches of the ground and dab the fresh cut using a Q-tip with full potency Roundup. Pouring a small amount into an old tuna can gives easier access. Be careful not to spill. If it is too close to the ground, cut both ends out of a 16 oz. can and stuff the plant inside. Apply roundup through the top onto fresh cut. You may end up with lots of cans around the yard to start, but this kills to the root so there is less regrowth from underground trailing roots. If roundup doesn't work within 1-2 weeks, switch to brush killer instead, always dabbing only on the fresh cut. This is the only way to get rid of evening nightshade in my area.

I would recommend pulling by hand. That is the way I keep ivy and dandelions in check. I let the kids play and while they are doing their thing, I am doing mine. Going around with roundup will still give you dead patches anyway if this stuff is so thick. Reseed the lawn after pulling.

So what is that weed? Took me years to rid my lawn of it. Now my clueless neighbors on both sides have allowed the weed to have it's way with their lawns.

Medicago arabica or polymorpha.

common name: burr medic