false indigo

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

• noun Any of several plants of the North American genera Amorpha and Baptisia of the pea family, formerly used as sources of blue dye.

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

• noun any of several plants of the genus Baptisia
• noun dense shrub of moist riverbanks and flood plains of the eastern United States having attractive fragrant foliage and dense racemes of dark purple flowers
• noun an erect to spreading hairy shrub of the Pacific coast of the United States having racemes of red to indigo flowers