The two most common types of burrs around here are agrimony [probably Agrimonia striata] and tick trefoil [Desmodium gangeticum]. The flowers are lovely, blooming in the late summer and fall.
Tick trefoil. The pink flowers are tiny.
They grow on stalks like tiny pea flowers. You can just see the new seed forming at the bottom of this pic.
Those burrs stick to everything.
Here are the burrs. They're cute, until they get on you and you can't get them off!
Agrimony looks a lot like a low blooming goldenrod.
Blow up this pic for an up-close view of the flower. It's pretty! But those burrs are awful.
This is where the idea for velcro came from.