‘Crimson Gem’ bracted viburnum (Viburnum bracteatum) is the first cultivar release from the Arnold Arboretum of Harvard University’s new plant introduction program, Arnold Selects.
This bracted viburnum’s one-of-a-flower was discovered over ten years ago by the Edwards Lab (then of Brown University, now of Yale) while conducting research in the Arboretum’s collections, and noted by Keeper of the Living Collections, Michael Dosmann. Reading his May 2010 database field check note, one can still feel Dosmann’s excitement: “inflorescences have red centers!” Indeed, blossoms have a rare sterile red floret in the center, resembling the herbaceous biennial Queen Anne’s lace (Daucus carota). The red floret is perched above the ivory ones, literally taking center stage. These unique flat-topped cymes are held on erect pubescent, 2-inch stems that are a whopping 1 ½ to 3 inches across.
In fact, the red floret can be enjoyed even before the shrub comes into full flower, while its pearl-colored neighbors are still in bud. But the real show starts when the enchanting inflorescences open in their entirety in late May to early June, showering the shrub, and revealing the ‘gem’ in the center of practically every single inflorescence. Foliage is also appealing: emerging leaves have an ephemeral reddish hue, notably visible along the margins and between veins. Leaves are 2 to 4 inches long and 1 ¼ to 2 ½ inches wide, and change to dark green as the season progresses. They are ovate with acuminate tips and serrate margins. Giving the plant its common name are the four persistent, bract-like stipules at each node (junction of leaf petiole and stem), as well as the two bracts below each inflorescence. Paired with leaf colors ranging bronze to maroon, the clusters of shiny oval to rounded fruits (drupes) are blue-black at maturity, providing autumn interest.
Viburnum bracteatum ‘Crimson Gem’
HARDINESS: Zone 5 to Zone 8 (-10°F to 20°F)
HABIT: Shrub, 7 to 10 feet tall with a slightly wider spread, rounded, dense
GROWTH RATE: Intermediate
SUN EXPOSURE: Full sun to part shade
SOIL CONDITIONS: Moist, well-drained, alkaline, adaptable
SEASONS OF INTEREST: Spring and autumn
PROPAGATION: Softwood or greenwood cuttings, 5,000ppm k-IBA
‘Crimson Gem’ was originally acquired as part of the Arboretum’s commitment to plant conservation. The Arboretum is a participating member of the Center for Plant Conservation (CPC), and has holdings of ten current indigenous North American species on the CPC threatened plant list. Founded in 1984 at the Arboretum, and with the national headquarters currently at the San Diego Zoo Safari Park in Escondido, California, CPC is unique partnership of conservationist organizations, such as botanical gardens and arboreta. Its aim is to preserve threatened North American plant taxa by ex situ conservation focused on acquisition and species stewardship.
Bracted viburnum is considered critically imperiled (global conservation status G1) and is endangered in the wild—mainly due to limestone quarrying, but also by clearing and logging operations. Only a few populations remain in the southeastern states of Alabama, Georgia, and Tennessee. In its current range, it is found selectively as an understory shrub growing in open deciduous woodlands and along rivers, particularly on the ledges of the Coosa River, which begins in Rome, Georgia before entering Alabama, and on the escarpment of the Cumberland Plateau (southern part of the Appalachian Mountain Plateau).
With CPC collections at the forefront of Arboretum institutional priorities in the mid-1980s, assistant plant propagator Rob Nicholson embarked on multiple expeditions to facilitate ex situ conservation. “I basically would go to the herbarium, compile a list of locales for the targeted species, and off I went,” Nicholson recalls. “Once in awhile I would connect with a botanist who knew a species and where to find it … but it was mostly solo hunting.” (Nicholson was a prolific collector for the Arnold and other institutions; see his account of the expedition to collect Pinus krempfii beginning on page 32.)
Nicholson’s investigations led him to travel to Tennessee and Georgia in October 1987, where scarce native populations of bracted viburnum are present. Twenty-one acquisitions from the very full weeklong Southeast State Expedition were accessioned. The trip was characterized by “long 16-hour days … and long miles.” Other taxa of interest on the trip included Fraser fir (Abies fraseri), endangered due to the balsam wooly adelgid; southern bush honeysuckle (Diervilla sessilifolia), considered threatened in its native state of Tennessee; and longstalk holly (Ilex collina), vulnerable with only 4,000 individuals in the wild.
With so many target taxa acquired, Nicholson’s CPC expedition was a success, but not to the extent that he could ever have imagined. Nicholson found the ‘Crimson Gem’ parent plant growing in Franklin County, Tennessee. Flowering in late spring, this bracted viburnum’s precious bloom could not have been observed when Nicholson made the collection on October 10th. Though it was in its fall fruiting phase, he recalls that no fruit was present, so he harvested a division—the sole means of preserving this crucial imperiled taxon. To hedge his bet, Nicholson took three divisions, two of which remain in the collections. Three days later, Nicholson visited Floyd County, Georgia, and collected other bracted viburnum divisions on the bluffs overlooking the Coosa River. These are also planted in the living collections, but don’t share their relatives’ unusual attribute.
Bracted viburnum divisions were cataloged upon receipt at the Arboretum, and ‘Crimson Gem’ was given the accession number of 1067-87. Plants were dutifully nurtured at the Dana Greenhouses at the Arboretum, and then aptly planted at the Viburnum Collection/Greenhouse border (likely so Nicholson could keep tabs on his valuable acquisition accomplishment) in 1992. In 2005, stem cuttings were taken of this endangered (and extraordinary) plant to increase the Arboretum’s ex situ holdings. The resulting clone, with the same ruby “gem,” was planted in the Leventritt Shrub and Vine Garden.
With over thirty years in the Arboretum landscape, ‘Crimson Gem’ has stood the test of time. It has provided outstanding seasonal interest, and has been reliable year after year in a shrub border. It would also be well utilized if planted as a hedge, or in mass. ‘Crimson Gem’ is adaptable to different soil conditions—it has certainly tolerated the Arboretum’s acidic soils just fine, though it is native to the alkaline soil of limestone woods. ‘Crimson Gem’ cuttings were just provided to nursery partners, so it will be several years before this new cultivar is available in the trade. However, it will no doubt be the jewel of gardens someday, and we can all have that magical “aha” moment—flowers have red centers!
Tiffany Enzenbacher was Head of Plant Production at the Arnold Arboretum from 2014 to 2023.
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