from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Any of several shrubs of the genus Physocarpus, especially P. opulifolius of eastern North America, having peeling or shredding bark and clusters of small white flowers.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any flowering plant of the genus Physocarpus.
From the many layers in its bark.(American Heritage® Dictionary of the English Language, Fourth Edition)
nine + bark, because the bark separates into many thin layers. (Wiktionary)