Our mystery seeds from last week were indeed tickseed sunflowers or common beggarticks, Bidens frondosa.
At least I think they are tickseed sunflowers. There are a number of similar species in the Genus Bidens. If you have a specimen you'd like to identify and you know a little botanical vocabulary, you might try this key.
The seeds of the tickseed sunflower form in these interesting seed heads.
The seeds then catch and stick to passing animals, in this case my jeans.
The flowers are small clusters of yellow. They are not very showy.
The leaves are compound, mostly in groups of three.
Tickseed sunflowers are native to North America and are often found growing in wet areas throughout the continent.
Although the plants can be considered to be a nuisance because of the sticky seeds, the seeds are much easier to remove than burdocks, and they are useful as food for wildlife.The plants are eaten by muskrats, rabbits, and caterpillars. The seeds are eaten by small rodents and birds, particularly waterfowl.
If you have a microscope and someone brings some home on their socks, be sure to take a peek at these fascinating seeds.