A bur (also spelled burr) is a seed or dry fruit in which the seeds bear hooks or teeth which attach themselves to fur or clothing of passing animals or people. The hooks or teeth can be irritants and very hard to get off of clothing, such as wool or cotton. It was the inspiration for Velcro.
Plants with burs are found in many genera:
*Acaena - Piri-piri
*Agrimonia - Agrimony
*Ambrosia - Ragweed
*Arctium - Burdock
*Bidens - Bur marigold
*Circaea - Enchanter's Nightshades
*Galium aparine - Goosegrass
*Geum - Avens
*Hackelia - Stickseed
*Osmorhiza - Cicely