Spiraea opulifolia

from The Collaborative International Dictionary of English v.0.48

Nine-bark \Nine"-bark`\, n. (Bot.)
   A white-flowered rosaceous shrub ({Neillia opulifolia}, or
   {Spiraea opulifolia}), common in the Northern United States.
   The bark separates into many thin layers, whence the name.
   [1913 Webster]