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The Snowbells of Korea Paul Meyer Styrax japonicus and obassia are small, spring-blooming trees that add a touch of elegance to any garden. Both species have gained in popularity I in recent years. When horticulturists think of the origin of than a hundred years, both species are little many oriental garden plants, Japan and China known beyond the circles of avid gardeners. most frequently come to mind. Though over- These Korean snowbells are among the hardi- looked until recent years, Korea is also home est of some one hundred and twenty Styrax to an exceptionally rich temperate flora and species. The genus, largely tropical and sub- contributes much to our American gardens. tropical, occurs in East Asia, the West Indies, When the Korean climate is compared with South and Central America, the Mediterra- that of the northeastern United States, strong nean region, and North America. similarities are evident, often more pro- J110WUe11 r.;,n:~ccu tl~am ~W~ii~i~iC~ w the climates of ~ij’isi~ juwiiia,ii~-jd~)allCJC most of Japan or China. When a species occurs Both the scientific epithet and common name across a wide geographical range that includes of this species obscure the full breadth of its parts of China, Japan, and Korea, the Korean natural range. It is indeed native to Japan, populations may be the most adaptable to the where it was first collected by Western growing conditions of the northeastern botanists, but it is also native to Korea, China, United States. Taiwan, and the Philippines. Japanese snow- Over the past fifteen years, a number of bell is a small tree, seldom much taller than American institutions-the U. S. National ten meters at maturity. When young, it can Arboretum, the Holden Arboretum, the be narrow and upright, or multistemmed and Arnold Arboretum, and the Morris Arbore- spreading. At maturity it broadens to become tum-have aggressively collected plants in a spreading, flat-topped tree. At the Morris Korea. I personally have participated in five Arboretum, a plant of unknown origin is at trips to Korea in search of trees and shrubs least seventy-seven years old, and measures 11I well adapted to the growing conditions of the meters tall by 12 meters wide, with a trunk eastern United States. diameter of 48 centimeters measured at breast During the course of these expeditions, I height. Another plant at the Arnold Arbore- have become interested in the genus Styrax, tum (AA #17334), raised from seed C. S. Sar- the so-called snowbells, represented in Korea gent collected in Japan in 1892, is still by two species, Styrax japonicus Siebold and thriving, having reached a height of 10.8 Zuccarini and Styrax obassia Siebold and meters, with a spread of 14.6 meters. Both Zuccarini-both outstanding horticulturally trees branch relatively low to the ground, and as small flowering trees. Although familiar to their trunks have a distinctly sculptural qual- American gardening connoisseurs for more ity. Bark on the trunk and older branches, dark 3 Close-up of the flowers of Styrax ~apomcus. Photo by P. Del ~edici. charcoal in color, is relatively smooth and niches from relatively well-drained lowlands sinewy. The leaves are small, dark green and to higher elevations. Most commonly found fine textured, and give the tree a refined in the understory and edges of oak-pine wood- appearance. lands, it grows in association with Quercus In late May, numerous pendulous flowers dentata, Q. aliena, Pinus thunbergiana, and create horizontal layers of white beneath the P. densiflora. already dense green foliage. When seen from During a 1984 United States National above, the bell-shaped flowers are scarcely visi- Arboretum expedition to Korea that I partici- ble, but from below the effect is striking. The pated in, along with collectors Barry Yinger, flowers are followed by pendant, oval, light- Sylvester March, and Peter Bristol, an interest- green fruits which, though interesting when ing, naturally occurring variant of Styrax examined closely, have little landscape merit. japonicus was spotted. The plant was grow- These fruits contain the poison egosaponin. ing in dry, sandy soil just a short distance from When the fruit is crushed, its poison can stun the coast of the Yellow Sea, exposed to salt fish if sprinkled on a pool of water. In the spray, periodic drought, and reflected heat. We Orient, it is used as part of a traditional fish- noted that this collection had particularly gathering technique. large, glossy, leathery leaves, and speculated Widely distributed in south Korea, Styrax that plants adapted to these stressful natural japonicus occurs in a variety of ecological conditions might be well adapted to analogous 4 The multistemmed trunk of Styrax japonicus (AA #17334J raised from seed collected m Japan m 1892 by C. S. Sargent. Photo by P. Del l~edici. urban conditions. Six-year-old seedlings from occurs, this earlier blooming tendency might this parent plant are now under evaluation in be a problem. Plants grown from seed are a relatively stressful site in the Morris Arbore- highly variable, some individuals growing tum parking lot. They range between 2 and upright with a strong central leader, while 2.3 meters tall and all are 3 centimeters in others are multistemmed and spreading. diameter. One seedling in particular, which J. C. Raulston of North Carolina State shows the distinct leathery leaf characteris- University Arboretum has promoted another tics of its parent, will be evaluated closely over interesting natural form of Styrax japonicus. the next few years for possible introduction. Collected in 1986 on Souhuksan Island off the Other young plants of Styrax japonicus of southwest coast of South Korea, this form is known Korean origin are growing throughout notable for its large flowers and exceptionally the Morris Arboretum. The oldest ones, rang- large, lustrous leaves, nearly twice the size of ing from 2 to 6 meters tall, are eleven years the typical species. The hardiness of this of age. Phenologically, these Korean collec- cultivar, which is of a more southern origin, tions bloom about one week earlier than other is not yet established. A specimen of this older plants in the collection of unknown clone at the Morris Arboretum continued to natural origin. In years when a late frost produce new growth late into the autumn in 5 The pendant frmts of Styrax japonicus. Photo by Peter Del l3~edici. 1991, and may, therefore, be particularly sus- characteristics, thus increasing the adaptabil- ceptible to winter damage. Though promising ity of this attractive landscape tree. for some regions, this clone requires further Snowbell evaluation before it can be widely promoted, Styrax obassia-Fragrant especially in the Northeast. Although grown in the U.S. since 1879, Sty- As one might expect with any widely dis- rax obassia is still rare. Like Styrax japonicus, tributed species, Styrax japonicus is quite it is a relatively small tree, usually under 10 variable. Prior to recent collections, most meters. Its large, bold, heart-shaped leaves, plants in cultivation in this country came measuring up to 20 centimeters across, cre- from a few individuals introduced at the turn ate a strong textural element in the landscape. of the century and therefore represented only Racemes of fragrant white flowers open in a narrow slice of the potential genetic diver- mid-May in the Philadelphia area (in late May sity of the species. Newly introduced popula- around Boston)-about a week before Styrax tions from Korea may, in time, result in japonicus. In the autumn, the leaves turn a improved winter hardiness, stress tolerance, clear yellow before falling away to expose a disease resistance, overall form, and landscape smooth, sculpted, gray trunk. On the young The flowers and fohage of Styrax obassia growmg m Harnsburg, Pennsylama. Photo by J. Horace McFarland, 1935. From the Archives of the Arnold Arboretum. ’ branches, the brown bark peels off in long, tion was probably based on plants collected narrow strips, often persisting for some time in warmer parts of its range in Japan and before falling away. China. In South Korea, my colleagues and I Like Styrax japonicus, S. obassia is a plant have collected populations north of Seoul of open woodland understory or edges. It where winter temperatures drop to -35 degrees grows best in moist well-drained soil and is Centigrade. We’re eager to test these popula- susceptible to drought, especially a newly tions in the hope that they will provide established plant. In many ways the natural individuals with greater winter hardiness. At habitat and horticultural adaptability of both the Morris Arboretum, these new populations these species are similar to those of the native have performed well so far. One plant, grown American flowering dogwood (Cornus from Korean seed collected in 1979, stands 5 florida). meters tall and 2.2 meters wide. Nine plants In older literature, Styrax obassia is from a 1981 expedition to Korea average 10 reported hardy only to Zone 6. This informa- centimeters in diameter, 5.4 meters in height, 7 and 4 meters in width. It is common for young plants to grow more than a meter a year when well sited. Dr. Michael Dirr of the University of Geor- gia has been testing the hardiness of a number of different individuals within this species in the laboratory. As one might predict, early results indicate that these northern populations show superior hardiness. In particular, one northern collection showed laboratory hardiness to at least -30 degrees Centigrade. Trees from this population are growing at the Morris Arboretum and the Arnold Arbore- tum, and seeds from these plants are now being distributed to interested nurseries for further evaluation.

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