To say that there are currently four species of Calycanthus that exist worldwide and leave it at that would be to discount the downright perplexing yet extraordinarily exciting buzz that has surrounded this genus during the past fifteen years.
Until the early 1980s, Western botanists and horticulturists understood the genus Calycanthus through three superficially similar species native to North America: Calycanthus floridus, C. fertilis, and C. occidentalis. It was the first, the so-called Carolina allspice, that was most used in horticulture, though its introduction to Europe in the 18th century was based on its economic potential as a cinnamon substitute. (Interestingly, all Calycanthus species possess an alkaloid poisonous to both livestock and humans.) Taxonomic detective work established justification for lumping C. fertilis and C. floridus together, with the former now known as C. floridus var. glaucus. However, the number of American species was returned to three shortly thereafter, with the recognition of a very rare species, the greenish yellow-flowered C. brockianus, from Georgia.
I know I will be berated by some for suggesting a lackluster appeal in such a thoroughly American genus of shrubs, yet had the status quo of Calycanthus continued, it is unlikely that I would be writing about them. The somber burgundy flowers of C. floridus and C. occidentalis do not read from any distance, and their fragrance is more cloying than sweet. Botanically interesting, yes. Part and parcel to our natural ecologies, absolutely. But definitely not possessing enough substance to warrant greater promotion for our landscapes.
In the early 1960s, however, things started to get very interesting. On a wooded mountain slope in Zhejiang Province in eastern China, botanists discovered a 10-foot deciduous shrub with all of the makings of a Calycanthus, yet with larger, white-blushed pink flowers and a thick, firm texture. It was described in 1963 as Calycanthus chinensis, then later reclassified as Sinocalycanthus chinensis. Under this name it made its debut into American horticulture in the early 1980s.
By 1985, there were only a handful of specimens in North America, mostly in botanical gardens, all causing a considerable stir (the specimen at the Brooklyn Botanic Garden was stolen soon after its inaugural blossoming in 1985). At about this time, one reached J. C. Raulston, then director of the North Carolina State University Arboretum in Raleigh. Under his tutelage in the late 1980s, student intern Richard Hartlage transferred pollen from Calycanthus floridus to the blossoms of Sinocalycanthus, and in the process lifted the genus Calycanthus from ornamental mediocrity forever.
The hybrid began blossoming three years later with large, magnolia-like, rose-red flowers, produced prolifically and precociously, showing a textbook intermediacy between both parents. It was named, after considerable, worldwide deliberation (and, sadly, after Dr. Raulston's untimely death) xSinocalycalycanthus raulstonii. The original hybrid clone was given the cultivar name ‘Hartlage Wine’. Further taxonomic work has since returned Sinocalycanthus to Calycanthus, making the hybrid the more euphonious Calycanthus xraulstonii.
Though the concept of a Calycanthus breeding program would have been unthinkable 20 years ago, the blossoming and subsequent introduction of ‘Hartlage Wine’ marks the starting point of a much expanded selection program. Dr. Tom Ranney of the NCSU Woody Plant Breeding Center has embraced the genus, making additional crosses of, and back crosses to, the same parents, and incorporating the genes of C. occidentalis and the yellow-flowered C. floridus ‘Athens’. His first release, C. ‘Venus’, is the most exciting new hybrid woody plant to be introduced into cultivation in recent history. Fast growing, it forms a dense rounded shrub to six feet high and five feet wide, with bold dark green foliage and a smothering of four- to five-inch white flowers throughout late spring and summer. Like both parents, it is adaptable to full sun or partial shade in any draining soil, in USDA Zones 5-10.
There are already other selections on the horizon, yet to be released—yellows, deep reds, bicolors, and those with good fragrance. This is a story that will continue to unfold in the years ahead. It is also a story that speaks volumes of the current pace and verve of global horticulture, and the importance of plant exploration and conservation. In the blink of an eye, the genus Calycanthus has been elevated to a garden-worthy gem by the discovery of a rare Chinese shrub—one that could have easily enough been lost before it ever became known.
TYPE OF PLANT: deciduous shrub
ORIGIN: North America and eastern China
HARDINESS: USDA Zones 5-10; Sunset Zones 3-9, 14-24
HEIGHT/SPREAD: 6 ft./5 ft.
LEAVES: large, narrow, ovate to elliptical, opposite, toothless
FLOWERS: 2-5 in. in diameter, whorl of tepals, in yellow, white, and reddish brown
SITE REQUIREMENTS: full sun to partial shade; average soil
PROPAGATION: by division, layering, or seed