Blackjacks or Bidens pilosa are a real curse at this time of the year if you have cats. Even if I stay out of the patches that grow in the area, my cats don't and they bring them home attached to their fur, go and lie on my bed and clean them off of themselves and leave them on my sheets or any stray item of clothing I may have left there.
Mutant dandelions, basically
This comes as a surprise to most people but the leaves of this kind of Bidens are eaten as spinach in some parts of Africa and they are actually highly nutritious. Perhaps I should get harvesting next year instead of complaining.
They are an introduced plant in Africa, coming from Europe and Asia and have sneaky habits, they only germinate and grow well during the height of summer when it rains frequently and then they grow and fruit very rapidly. I keep them under control for most of the year and then suddenly it rains heavily for three weeks and I look again and they have gone from nothing to seed-heads and we are back to square one in the control department.