Photo by Sue Lannon.
Botanical name: Wisteria frutescens
Common name: American wisteria
Family name: Fabaceae (Pea Family)
Native range: Eastern and central North America
Location in Duke Gardens: Historic Gardens, Blomquist Garden of Native Plants
USDA Hardiness Zones: 5-9
Each April, visitors near and far look forward to seeing the lovely purple cascades of the iconic wisteria crowning the Cindy Brodhead Pergola at the top of the Terrace Gardens. But how is it possible that this wisteria is in flower when so much of the wisteria in the area has already come and gone?
The deceptively simple answer is that “wisteria” isn’t a single kind of plant, but a generic term for a group of closely related species in the pea family possessing different characteristics. Most of the wisteria varieties found in forested woodlands across North Carolina are the non-native Chinese wisteria (Wisteria sinensis) or Japanese wisteria (W. floribunda), which are highly aggressive and frequently escape into the wild from cultivated plantings. Meanwhile, the wisteria in the Terrace Gardens is the native American wisteria (W. frutescens), which blooms a few weeks later than its Asian counterparts. Part of the reason for this delay is order of operations—Asian wisteria flowers emerge before the leaves, while American wisteria only blooms after its leafy canopy has filled out.
Although American wisteria is often mistaken for Asian wisteria, there are several other “tells” that help to identify it at a glance, even later in the year when flowers are not visible. One is habitat—American wisteria is more common in the North Carolina Coastal Plain than in the mountains or Piedmont, which tend to be dominated by the introduced Asian species. American wisteria can also be distinguished by its long, dangling seedpods, which are smooth instead of fuzzy.
Due to its love for bottomland forests and wet thickets—where it can be supported by sturdier vegetation—American wisteria is commonly known as “swamp wisteria,” though it can also thrive when planted in drier or well-drained locations. Many taxonomists divide American wisteria into two subspecies based in part on their geographic range. Wisteria frutescens var. frutescens is found in the eastern half of the species’ range from southern Virginia to Florida and west to Texas and Arkansas, while W. frutescens var. macrostachya (sometimes labeled as W. macrostachya in the horticultural trade) occupies the western half from Indiana and Missouri to the Appalachian Mountains.
One fun fact about wisteria is that different species twine in different directions around their supports. Japanese wisteria twines clockwise from lower right to upper left, while both American and Chinese wisteria twines counterclockwise from lower left to upper right. Botanists have also identified a naturally occurring hybrid between Japanese and Chinese wisteria (Wisteria ×formosa), which has traits from both parents, but generally twines counterclockwise.
Landscape architect Ellen Biddle Shipman’s original vision for the Terrace Gardens included Chinese wisteria atop the pergola, which was planted as part of the site’s construction in late 1938 and early 1939. As part of restoration efforts in honor of the 75th anniversary of the pergola’s dedication, the original planting was replaced with the slower-growing American wisteria in order to prevent long-term damage to the structure. As Chinese wisteria is now officially classified as an invasive species by the state of North Carolina, the shift serves as a living testament to Duke Gardens’ commitment to sustainability and environmental stewardship.
While the Historic Gardens wisteria is unquestionably the most famous planting of this species in the Gardens, it’s difficult to get a good look at the flowers because they are so high overhead. For a closer look, visitors must seek out a more accessible specimen in the Backyard Wildlife Garden in the Blomquist Garden of Native Plants. ‘Amethyst Falls’ is a popular and widely available dwarf cultivar that is especially slow-growing, making it an excellent choice for patios, trellises, and other small, contained spaces.