Photo credit: epicgardening.com
SPECIES SPOTLIGHT: WISTERIA
This month, we are focusing on three species of wisteria that you may find in both cultivated and wild/naturalized forms in New York and New Jersey: the nonnative Chinese Wisteria (Wisteria sinensis) and Japanese Wisteria (Wisteria floribunda) species and the native American Wisteria (Wisteria frutescens).
All three species of wisteria are in the legume family and are hardy, fast-growing woody vines that twine around most any structural support, including our native trees! Wisteria prefers moist, well drained soil and thrive in full sun, but have adapted to grow in poor quality soils and partially shaded regions as well. They have been historically popular ornamental plants due to their showy, fragrant lavender-purple flowers that hang in dangling clusters about 6-20 inches long. Wisteria blooms spectacularly in the spring in the Eastern United States with the nonnative Asian species typically blooming in May (in most parts of New York and New Jersey) and the American variety a few weeks to a month later. The leaves on all three species are alternate and pinnate and can be almost a foot long with wavy-edged leaflets that have a smooth margin.
Chinese Wisteria leaf structure at different age structures. Photo credit: USDA, Natural Resources Conservation Service
The two nonnative, Asian species of wisteria are currently Tier 2, or “emerging” species in the Lower Hudson PRISM region, meaning they are just starting to become established in natural areas. Chinese and Japanese Wisteria are aggressive, fast growing woody vines that can quickly spread and create dense thickets. When wisteria escapes from cultivation and establishes in natural areas, it can displace native vegetation through shading and interfering with nutrient uptake, even strangling and felling trees with its thick, heavy vines. Wisteria can sprout from seed or through vegetative reproduction and all forms of the plant are toxic making it an even more formidable invader.
American Wisteria is native to the southeastern United States and does not occur naturally in the New York/New Jersey region. So we would expect it to only be found in places where it was planted. But does it? Let’s find out what species are growing in our natural areas.
Distinguishing between the different species can be tricky at first glance, but there are some key characteristics to look for that with a little practice can help tease them apart. In addition to blooming later in the year than the Asian species, American Wisteria tends to grow in a more shrub-like fashion and has flower clusters that are shorter and rounder (i.e., pine-cone-shaped) versus the more climbing nature and elongated flower clusters of Chinese and Japanese Wisteria. One clear way to distinguish between the American and Asian species is by looking at their seed pods – American Wisteria has seed pods that are smooth and hairless versus Chinese and Japanese Wisteria’s velvety, hairy seed pods. Check out the below graphic from bugwood.org for a closer look.
The easiest way to distinguish between the two Asian species is to look at the twining direction of their vines. When viewed at eye level, Chinese Wisteria stems ascend a tree or other support diagonally up to the right. Japanese Wisteria spirals in the opposite direction, ascending diagonally up to the left (see picture comparison below courtesy of Maryland Invasive Species Council). You can also distinguish between the two by looking at their leaf structure: the Japanese species typically has more leaflets per leaf (13-19) compared to Chinese Wisteria (7-13 leaflets per leaf). The timing of their blooms also differ: The flowers in a cluster all bloom at the same time in Chinese Wisteria, but in Japanese Wisteria, the flowers lower in the cluster bloom first and progress in blooming chronologically upward. So, if you see only part of a cluster blooming at any time, it’s likely the Japanese species!
So, when photographing these species it’s important to not only take pictures of the flower but also the direction of twining and the leaf showing the number of leaflets so that the species can be accurately identified.
In addition, when reporting observations of these species, it is important to note if you are reporting a planted individual such as one that is growing in a garden or home landscape (cultivated) versus one that is growing in a natural area (wild).
For more information on these species, please check out the following sources that served as good references for this article!
Wisteria: Criteria for Deliria?! Written by Michael Ellis, March 1, 2016. Maryland Invasive Species Council. http://mdinvasives.org/iotm/march-2016/
Native Alternative to Invasive Imported Wisteria. Today’s Homeowner. https://www.todayshomeowner.com/native-alternative-to-invasive-imported-...
Chinese and Japanese Wisteria. Home and Garden Information Center. University of Maryland Extension. https://extension.umd.edu/hgic/topics/chinese-and-japanese-wisteria