ninebark, any plant of the genus Physocarpus of the family Rosaceae (rose family). Ninebarks are North American (one is Asian) deciduous, hardy, spring-blooming shrubs, with thin bark which peels off in many layers. The most common American species is P. opulifolius, found along rocky streams E of the Rockies. Ninebarks are similar to the closely related spiraeas and are also cultivated as ornamentals. Ninebarks are classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Rosaceae.
"ninebark." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (September 23, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/ninebark
"ninebark." The Columbia Encyclopedia, 6th ed.. . Retrieved September 23, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/ninebark