1. Tall Ninebark, Pacific Ninebark: Physocarpus capitatus - Shrub to 12 feet. Flowers small, white, and arranged into spherical clumps. Pistils generally 3-5. Leaves simple, and palmately lobed (typically with 3 lobes).

2. Mallow Ninebark: Physocarpus malvaceus - An erect, loosely branched shrub up to 6 feet tall. The alternate leaves are maple-like with 3 palmate lobes, the margins double toothed. The flowers are small, white, and borne in terminal corymbs. Pistils generally 1-2. Similar to Physocarpus capitatus but with smaller leaves and corymbs, and smaller growth habit.