The Collaborative International Dictionary of English v.0.48:

Quaking \Quak"ing\,
   a. & n. from Quake, v.
   [1913 Webster]

   Quaking aspen (Bot.), an American species of poplar
      (Populus tremuloides), the leaves of which tremble in
      the lightest breeze. It much resembles the European aspen.
      See Aspen.

   Quaking bog, a bog of forming peat so saturated with water
      that it shakes when trodden upon.

   Quaking grass. (Bot.)
   (a) One of several grasses of the genus Briza, having
       slender-stalked and pendulous ovate spikelets, which
       quake and rattle in the wind. Briza maxima is the large
       quaking grass; Briza media and Briza minor are the
       smaller kinds.
   (b) Rattlesnake grass (Glyceria Canadensis).
       [1913 Webster]

WordNet (r) 3.0 (2006):

quaking aspen
    n 1: Old World aspen with a broad much-branched crown;
         northwestern Europe and Siberia to North Africa [syn:
         quaking aspen, European quaking aspen, Populus
         tremula]