V. opulus var. opulus* (European Cranberrybush, Guelder-rose) is non-native (Asia). Further, many cultivars are also available, and the two varieties hybridize in the wild.
|Viburnum opulus var. opulus |
| Viburnum opulus var. americanum|
| Viburnum opulus (presumably var. opulus)|
| V. opulus var. opulus|
|V. o. var. americanum; Virginia Tech Forest Resources and Env. Conservation|
| V. o. var. americanum|
|V. opulus; Invasive Plant Atlas|
Flowering dates: May through June
Fruit ripening dates: August through September
Seed dispersal dates: March through May
Distinguishing between the two varieties and hybrids can be difficult. Here are the main characteristics (from the key at Michigan Flora online, and "Viburnum opulus var. americanum, A Technical Conservation Assessment" [PDF], USDA Forest Service).
- Large glands at base of petiole: americanum 0.4–0.8 mm long (rarely absent), usually stalked with the apex convex and flat topped; opulus 0.9–1.5 mm long, usually sessile and with the apex concave and indented
- Groove on upper surface of petiole: americanum broad and flat-bottomed; opulus narrow and v-shaped
- Stipules: americanum thickened at top; opulus threadlike (this not entirely reliable)
Seeds can probably not be distinguished.
These fruits are generally unpalatable to birds and persist through the winter. Contrary to urban legend, they do not require repeated freeze-thaw cycles to become appealing to birds. They are typically eaten in early spring (mostly by Cedar Waxwings, Bombycilla cedrorum) when supplemental protein is available to offset the highly acidic composition of the fruits. See Jones and Wheelwright 1987 and Witmer 2001 for details.
- Species profiles at USDA Plants Database: V. o. var. americanum, V. opulus [var. opulus]
- University of Wisconsin-Steven Point Robert. W. Freckmann herbarium species profiles: V. o. var americanum [trilobum], V. o. var. opulus
- Trees, Shrubs, and Woody Vines of Illinois species profile of V. o. var. americanum
* Listed as invasive in natural areas by the Invasive Plant Atlas of the United States.
(Numbers in photo captions are photo credits, listed in the "Photo Credits" tab at the top of the page)