Wisteria is a popular flowering vine, but its origin in North America is not straightforward. The genus Wisteria includes species native to the United States and others imported from Asia. Understanding the difference is important for gardeners and property owners. The confusion stems from the visual similarities between the native and non-native varieties, which both produce cascading flowers. Distinguishing between the two groups relies on their growth habits, ecological impact, and subtle physical characteristics.
The American Species
North America is home to native varieties, primarily Wisteria frutescens (American Wisteria) and Wisteria macrostachya (Kentucky Wisteria). These species are distributed across the southeastern and south-central US, typically found in moist thickets and along stream borders. Unlike imported vines, the American species exhibit a restrained growth habit, rarely reaching the destructive potential of foreign counterparts.
The native wisterias support the local ecosystem and are well-suited for US gardens. Their flowers, usually blue-purple to lilac-colored, appear in late spring or early summer after the leaves have fully emerged. These blooms are a food source for native pollinators, such as the Long-Tailed Skipper butterfly. American Wisteria’s flower clusters, or racemes, are typically shorter, measuring three to six inches in length.
The Imported Species
The majority of wisteria seen climbing structures are the two main imported species: Wisteria sinensis (Chinese Wisteria) and Wisteria floribunda (Japanese Wisteria). These species were brought to the US in the early 1800s for their ornamental value, prized for their abundant and fragrant flowers. The imported varieties are the source of most ecological and structural concerns, as they are considered invasive species in many US regions.
Chinese and Japanese Wisteria are fast-growing, woody vines that quickly escape cultivation and overwhelm natural areas. They cause damage by growing over and smothering native trees and vegetation. Their thick, heavy vines can physically strangle or girdle tree trunks and branches, leading to the death of mature trees. The imported wisterias thrive in a wide range of conditions, contributing to their rapid spread in diverse forest types.
These non-native vines are known for their long flower racemes, often 6 to 20 inches in length, and sometimes longer in the Japanese variety. Unlike the native species, these showy flowers typically bloom in April or May, before or just as the leaves begin to emerge.
Key Differences for Identification
Distinguishing between the native and imported wisteria species relies on observing a few distinct physical traits. One reliable characteristic is the texture of the seed pods. The native American Wisteria produces completely smooth seed pods, while the pods of both Chinese and Japanese Wisteria are velvety or fuzzy to the touch. These brown, bean-like pods often persist into the winter, making this a useful year-round identification point.
Another difference is the direction the vine twists as it climbs a support structure. The Japanese Wisteria twines in a clockwise direction. In contrast, both the native American Wisteria and the Chinese Wisteria twine counter-clockwise.