glochid

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One of the minute barbed hairs or bristles on certain plants, such as the prickly pear.

Wiktionary

1. n. a form of small, detachable, irritant spine occurring in dense clusters in the areoles of certain cacti such as prickly pear. Typically glochids are short, straight, and microscopically barbed. When stuck into the skin of anyone touching the plant, they detach and remain in the skin when the victim moves away.

WordNet 3.0

1. n. a barbed spine or bristle (often tufted on cacti)