The Styracaceae family includes a number of very ornamental flowering trees native to the temperate zones of North America and Asia. Perhaps the most frequently encountered genera in this family are the Styrax, the Halesias and the Pterostyrax. All the species described here are hardy in western New York. Unfortunately, none of them are common in gardens and they all deserve greater attention because of their ornamental value and general pest resistance. I have seen very little deer browse on any of the species.
The name Styrax is derived from the classical Greek name for the Eastern Mediterranean species, Styrax officinalis, which produces a fragrant resin, called gum storax, much prized in ancient times. It is a small shrub, hardy to Zone 9, and rarely found in arboreta. (The modern herbal compound storax is derived from the sweetgum tree, Liquidambar styraciflua, a member of the witch hazel family, Hamamelidaceae.)
The Japanese Snowbell is probably the most well known of the Styrax family. As the name suggests, it is native to Japan, but also to China, Korea, and the Philippines. It is a small tree, maturing at about 20' to 25' with equal spread. The bright green, lustrous leaves are quite small, acuminate, with finely toothed edges, and cast a very light dappled shade, providing a good environment for under plantings of small shrubs and perennials. The leaves do not color well in the fall and are often held late, dropping green after a few hard frosts.
Late May or early June in western New York is the flowering time for this species. The white bell-shaped flowers are arranged along the branches in groups of 3 to 6, each held on a 1" to 1 1/2" long pendulous stalk, hanging below the leaves. The five petals are slightly recurved, exposing the yellow stamens. They have a slight fragrance, but you have to get your nose right in there to appreciate it. The flowers are followed by rounded drupes, light gray in color, containing a single (occasionally a double), hard-shelled seed. The seeds sometimes hang on through the winter, providing seasonal interest.
The bark is smooth dark gray, with irregular narrow brown fissures, and often has a fluted appearance, reminiscent of the American hornbeam (Carpinus caroliniana).
The species likes a moist, organic, acid soil in full sun to part shade, but is quite tolerant of neutral soils and less than ideal conditions. Frost pockets can cause bark splitting, especially on young trees. Some individuals have a tendency to be low-branched or multi-stemmed, and must be pruned regularly to maintain a single trunk. On tree-form varieties pruning is generally not necessary, except to remove damaged and crossing branches. All in all, Japanese Snowbell is a carefree, beautiful addition to any garden.
There are a number of cultivars available, the most common being 'Carillon', 'Emerald Pagoda', and 'Pink Chimes'. S. japonicus 'Carillon' is a small, graceful, weeping form, about 8' high, with flowers and foliage similar to the species. 'Emerald Pagoda' is an upright form with larger, darker green leaves and larger flowers, introduced from Korea by J.C. Raulston and the US National Arboretum. 'Pink Chimes' is a pink-flowering form of small tree, which appears to come true from seed. My specimen is a quite prolific seeder and every seedling dug up from under the tree has produced pink flowers.
A less common relative is the Fragrant Snowbell from Korea, Japan and China. This species is unlike the Japanese Snowbell in that the leaves are very large, rounded, and densely pubescent on the underside. Fall color is at best a weak yellow. The flowers are white bells produced in late May in 6" to 8" long drooping racemes, and are sweetly fragrant. The flowers open from the base to the apex of the raceme over a period of approximately 3 weeks. The fruit is similar to that of S. japonicus, again containing one or occasionally two hard brown seeds about 1/2" in size. The bark is smooth dark gray-brown with narrow, lighter fissures. The trees are more likely than S. japonicus to produce a single trunk and they tend to grow in a slight zigzag fashion, creating a very interesting effect. An additional attraction is the bark on one year-old wood, which is a rich brown and peels away when growth begins, creating many small chestnut curls.
Fragrant Snowbell should be planted in moist organic acid soils for best performance, and seem to benefit from high canopy shade, although full sun is acceptable with sufficient moisture. Since the large leaves tend to obscure the flowers somewhat, a location on a slope is recommended, from which one can look up and see the flowers better. Like the Japanese Snowbell, the Fragrant Snowbell does not provide good fall color, but makes up for it with the other seasonal interests of flowers, leaves and bark.
In Rochester, there is a collection of plantings of S obassia along the slopes of Pine Valley in Durand Eastman Park. After seeing these in bloom one year I decided I needed to have one in my garden. Not finding any locally, I had to seek a mail-order source, and finally found one in a nursery in Washington State. When the tiny plant arrived, I realized I had seen one on my farm and not recognized it. While clearing back the woods from my Christmas tree plantation the previous winter, I had encountered a tree I knew to be exotic from the smooth dark gray-brown zigzagging trunk. But I could not identify it immediately. I had cleared the brush from around it to give it room to grow. The tree stood about 8' tall with a trunk about 2" thick. After receiving the seedling from Washington, I realized the tree in the woods was S. obassia. How it got there is a mystery; to my knowledge, there are no specimens in the area, but the species is known as a mast producer in Japan, and the seed have been carried in a turkey gut. But whatever the source, I do appreciate it's magnificent show every year.
In my experience, propagating S. obassia from seed is much more difficult than S. japonicus, and growing seedlings on is also more of a challenge, but worth the effort. I believe that S. obassia is less tolerant of soil conditions than S. japonicus, but somewhat more cold hardy.
The American species of Styrax is even less common than S. obassia, being virtually unknown in gardens and almost impossible to find in catalogs, although I note that Seneca Hill Perennials is offering it. S americanus is shrubbier than its Asian cousins, and is found in the wild along stream banks and lowland areas from Virginia to Florida and west to Arkansas, with isolated populations in the Kankakee River area of northeastern Illinois, and in Indiana. The one I have seen in Ohio's Holden Arboretum was a rather wispy individual, about 5' high, and growing in the shade of large trees. It was not in bloom and could have quite easily gone unnoticed if I hadn't been looking for it. There is a specimen in the Arnold Arboretum, in Boston, which I have not seen.
Growing 6' to 8', S. americanus looks like a small shrubby version of S. japonicus, with similar leaves and flowers. The flowers are more delicate, however, with narrower recurved petals and much more fragrant, rivaling those of S. obassia. The flowers occur singly at leaf axils and hang below the leaves on 1/2" long pedicels.
Like most Styrax, a moist soil is preferred, and a location in part shade or morning sun. This species is reported to be cold hardy to Zone 5.
Halesia tetraptera (carolina)
A more common member of the Styrax family is the Carolina Silverbell. The Halesia genus is named after Reverend Stephen Hales, an 18th century physiologist, chemist and inventor from London. Hales invented a method of fumigating wheat with sulfur to prevent weevil infestations, a ventilation method for prisons and ships, and is reputed to have been the first to measure blood pressure, using a horse as patient and a goose windpipe as a tube to transfer the blood to a glass measuring tube.
The Carolina Silverbell is naturally an understory tree found on wooded slopes and stream banks from West Virginia to Florida. Under cultivation it can reach 30' to 40', although there are wild specimens in the Smoky Mountains approaching 100' (possibly the variety 'monticola'). It tends to be multi-stemmed or low branched. Some planted specimens I have seen are definitely shrubby, and may have been pruned back for that effect or perhaps be a different species or variety, such as H. tetraptera var. parviflora. Even large old trees can be rejuvenated by cutting the trunk to the ground and letting new shoots grow from the stump. The trunks are dark gray-brown with narrow, longitudinal darker stripes, very reminiscent of the Styrax spp. In older specimens the bark becomes scaly with flat ridges.
The leaves emerge covered with a white tomentum, and then change to a bright green, glabrous above and pubescent beneath. Fall color is yellow to yellow-green, and rarely effective. Leaf margins are very finely toothed. In mid May, white, bell-shaped flowers emerge before or with the unfurling leaves, and hang down from the one-year old stems on 1" long stalks in clusters of 2 to 5. The flowers are similar to those of Styrax, but consist of 4 fused, shallowly lobed, petals forming a more closed bell shape. After about two weeks they fade to a pinkish color. Trees will begin to flower at a young age, perhaps at 6' or so.
The flowers are followed in the fall by green, oblong drupes with four wings (hence the specific epithet: in Greek tetra means four and ptera wings). Inside the soft, green fleshy outer skin is a very hard corky seedcase, containing 1 to 3 embryos. Most of the seedcase seems to be empty or crisscrossed with corky extensions. As the leaves fall, the drupes turn brown and can persist on the tree through the winter, which can be quite ornamental. The outer wings and mostly hollow interiors of the seeds seem to argue for a wind dispersal system, but the seeds are so big, to 1 1/2" long, and so firmly attached to the branches that this seems a contradiction. Perhaps they are designed to float down streams in spring, when the seeds finally loose their grip on the branches.
Like their cousins the snowbells, Silverbells prefer a moist, humusy, acidic soil. They will flower equally well in sun or shade. They are generally very forgiving plants and pest-free. Chlorosis can be a problem on high pH soils, but can be quickly remedied with applications of chelated iron/manganese. This species is hardy to Zone 4.
Once thought of as a separate species, Halesia monticola is now considered by most authorities to be a variety of H. tetraptera, with larger flowers and overall larger dimensions. There are several cultivars in the trade, but none are common. There is a pink-flowered variety, called 'rosea', a large-flowered variety called 'Wedding Bells', and several variegated forms, the stability of which is questionable.
The Two-winged Silverbell is very similar to H. tetraptera, but is generally a little smaller in stature and, as the name suggests, produces seedpods with only two wings. The flowers are similar to those of H. tetraptera but are more deeply lobed, and arrive about two weeks later. H. diptera also flowers profusely at a young age, often 3 to 5 years old. Its natural distribution is more restricted than H. tetraptera, confined to moist areas from South Carolina to Florida, but is remarkably hardy, at least to Zone 5.
One cultivar of H. diptera, 'magniflora', has larger flowers, measuring up to 1 1/3" and is rarely available.
The Fragrant Epaulette tree is another native of Japan, rarely seen in American gardens. Generally multi-stemmed, reaching about 20', this species forms a rounded open crown with spreading branches. It is fairly fast growing, adding up to 2' a year, and begins flowering at about 8'. The leaves are similar to those of the Silverbells, being oblong-ovate, bright green above and somewhat pubescent underneath, with minutely toothed margins. As with other members of the family, fall color is not remarkable.
The lightly fragrant flowers emerge after the leaves in June, and are creamy white in large panicles 5 to 10" long, which hang down below the leaves and (exercising ones imagination to the fullest) resemble epaulettes on military uniforms. The flowers are followed by small, 1/2" long bristly (hispid) 10-ribbed drupes, which tend to persist throughout much of winter.
The resemblance to other members of the Styracaceae is seen in the smooth dark gray-brown bark with lighter orange striations. Older stems tend to exfoliate in paper thin strips. Young stems are a lighter orange-tan.
The Epaulette tree is rated hardy to Zone 4. It prefers a moist, well-drained (what tree doesn't?) acid soil, in full sun. Best flowering is achieved in hot, sunny conditions. Although reported to be hardy, pest free, and tolerant of wind, drought and clay, I have experienced considerable dieback with this plant, for reasons not entirely understood, but possibly related to rapid changes in temperatures, a quite common occurrence in western New York. Nevertheless, the plants continue to send up new stems with abandon.
The northeastern United States is blessed with a climate capable of supporting an amazing variety of plants from all over the globe. Nevertheless, perhaps less than 10% of the possible species (never mind varieties) are ever seen in gardens and landscapes. The Styrax family contains some of the other 90%, including a number of beautiful trees for the discerning gardener. The Snowbells and Silverbells offer a more subtle beauty than the brazen, but somewhat gaudy, crabapples and cherries, and add richness and diversity to the landscape. An added bonus is their apparent unpalatability to deer.Further Reading Dirr, Michael A. 1998 Manual of Woody Landscape Plants, 5th Edition, Stipes Publishing. Elias, Thomas S. 1989 Field Guide to North American Trees. Grolier Book Clubs Inc. Hightshoe, Gary L. 1988 Native Trees, Shrubs and Vines for Urban and Rural America. Van Nostrand Reinhold. Poor, Janet M. (ed) 1984 Plants That Merit Attention, Volume 1: Trees. Timber Press. Stearn, William T. 1996 Stearn's Dictionary of Plant Names for Gardeners. Timber Press.