The Collaborative International Dictionary of English v.0.48:

Alum root \Al"um root`\ (Bot.)
   A North American herb (Heuchera Americana) of the Saxifrage
   family, whose root has astringent properties.
   [1913 Webster] Alum schist

WordNet (r) 3.0 (2006):

Heuchera americana
    n 1: plant with basal leaves mottled with white and flowers in
         lax panicles on erect stems [syn: rock geranium,
         Heuchera americana]