The Collaborative International Dictionary of English v.0.48:

Blackroot \Black"root`\, n. (Bot.)
   See Colicroot.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Colicroot \Col"ic*root`\, n.
   A bitter American herb of the Bloodwort family, with the
   leaves all radical, and the small yellow or white flowers in
   a long spike (Aletris farinosa and Aletris aurea). Called
   sometimes star grass, blackroot, blazing star, and
   unicorn root.
   [1913 Webster]