Physocarpus is a genus of flowering plants commonly called ninebark. Ninebark encompasses about ten species of tree-like shrubs. Many of these species are used for ornamental purposes, and some are often found in the wild. Most species are native to North America, particularly around mountain regions in the United States, though one species is native to Asia. This genus is found in the rosaceae, or rose, family.
Species are all deciduous bushes of varying heights and widths. They usually have clusters of small white or pink flowers which bloom in May and June. Flower clusters are generally 3–5 inches (7.6–12.7 cm) across, and fruit is usually red and berry-like, also appearing in clusters. Multi-branched, with three to five lobed, maple-like leaves, the width, or spread, of these plants is usually equal to their height. Physocarpus species can be propagated by cuttings or by seeds.
The most distinctive aspect of these bushes, however, is the feature that gives them their common name. Bark is generally yellowish-orange or reddish-brown and peels off in large strips. Every species' bark peels, and branches are generally covered with strips of peeling bark. Because of this continual peeling, shrubs are said to have nine layers of bark.
Both Physocarpus capitatus, or Pacific ninebark, and Physocarpus monogynus, or mountain ninebark, are commonly found in the north western United States. Usually about 5 feet (1.5 m) tall capitatus ranges from Utah and Montana in the United States into British Columbia in Canada. Though this species grows wild — sometimes under trees like sycamores — it is often cultivated for gardens.
Monogynus is found along the Rocky Mountains and into Nevada. It is one of the smallest species in this genus, only reaching a maximum of 4 feet (1.2 m) tall. This shrub is vase-shaped and thrives in canyon bottoms, mountain slopes, and anywhere the soil is well drained. The berries are often eaten by birds.
Not all North American species are found in wester North America, however. Physocarpus opulifolius, or common ninebark, ranges from Quebec south through Tennessee. This species may be 6–10 feet (1.8–3 m) tall and is most commonly used in landscaping and gardening for grouping and bordering purposes or as a natural screen.
Physocarpus amurensis, or Asian ninebark, is the only species in the genus not found in North America. Called feng xiang guo in Chinese, Asian ninebark is found primarily in China and is often used for ornamental purposes. These shrubs are normally about 10 feet (3 m) tall.