blowball

from The Century Dictionary.

• noun The downy head of the dandelion, salsify, etc., formed by the pappus after the blossom has fallen.

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

• noun The downy seed head of a dandelion, which children delight to blow away.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The downy seed head of a dandelion, a dandelion clock.

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

• noun any of several herbs of the genus Taraxacum having long tap roots and deeply notched leaves and bright yellow flowers followed by fluffy seed balls