beggar's lice

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several plants, such as bur marigold, stickseed, or tick trefoil, having small, often prickly fruits that cling readily to clothing or animal fur.
• noun The fruit of any of these plants.

from The Century Dictionary.

• noun An English name of Galium Aparine, or goose-grass, given to it because its burs stick to the clothes, and somewhat resemble lice.
• noun The name given in the United States to species of Bidens and to Echinospermum Virginicum, the seeds of which have barbed awns which cling persistently to clothing. Also called beggar's-ticks.
• noun A name of the European stickseed, Lappula Lappula; of the hound's-tongue, Cynoglossum officinale; of the species of Meibomia (see beggar-weed, 2); and probably of other plants with adhesive seeds or pods.

from the GNU version of the Collaborative International Dictionary of English.

• (Bot.) The prickly fruit or seed of certain plants (as some species of Echinospermum and Cynoglossum) which cling to the clothing of those who brush by them.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various tropical and subtropical plants having trifoliate leaves and rough sticky pod sections or loments
• noun Eurasian and North American plants having small prickly nutlets that stick to clothing