Styphnolobium japonicum: An ancient tree thrives in the city

If a Styphnolobium japonicum grows in your neighborhood, you may have first noticed it during the dog days of summer—a time when fluffy panicles of creamy white flowers stand out against the lustrous green leaves of its broad-spreading crown. Relatively unfamiliar to most Americans, this beautiful and exotic tree has traveled a long and fascinating journey from the ancient temples of the Orient to its new role as an urban street tree. Although it has been in cultivation in the West for nearly 250 years, it has spent most of those years in relative obscurity, relegated to botanical gardens and arboretums. But the development of improved cultivars and a new appreciation of its tolerance for the urban environment is leading to a renaissance for this tough and versatile tree.

Early origins

Styphnolobium japonicum (previously Sophora japonica) is known by an assortment of common names: Japanese Pagoda Tree, Chinese Scholar Tree, or sometimes more simply as Pagoda Tree or Scholar Tree. In contradiction to its botanical name, the Pagoda Tree is actually native to China, although it has been cultivated throughout the Orient, in Japan as well as China, for thousands of years.

Known as “huái shù”(1) in China and “enju”(2) in Japan, the Pagoda tree is native to the dry plains of western China. The renowned plant hunter Ernest H. Wilson reported that it was “common in western Hupeh and Szech’uan and is an important feature of vegetation in the arid valleys of western Szech’uan.”(3) As far back as the Shu dynasty (1122-240 B.C.), the Pagoda Tree already had a tradition of serving as a memorial tree for government officials (4) and was often planted near Buddhist shrines. It also had many practical uses. Its wood is strong and flexible, and was used for building ships and carriages, as well as for kitchen utensils and woodworking crafts. A yellow dye could be extracted by baking and boiling its flowers, and a tea made from its bark was thought to be useful in stopping bleeding and curing burns. The Pagoda tree is still very common in the East, and is used as both an ornamental and a street tree throughout China.(5)

Introduction to Europe

For a long time, however, China was closed to outsiders and most of the Chinese flora was unknown to the Western world. Some of the earliest foreigners to penetrate into China were Jesuit missionaries who were admitted during the 18th century. One of these missionaries, Pierre d’Incarville, was responsible for sending some of the first botanical material out of northern China, and seeds of Styphnolobium japonicum were included in one of his early shipments.

Pierre d’Incarville had journeyed to China in 1742 as part of a team invited to advise the Emperor Ch’ien Lung on the cultivation of European flowers to be used in his “Garden of Perfect Brightness”.(6) Although not a botanist by early training, d’Incarville studied for six months at the Paris Jardin du Roi in preparation for his trip, as this visit to Peking would be the first opportunity to gather Chinese plants so far north.(7)

Upon arriving in Peking, d’Incarville found that there were many obstacles in his efforts to send Chinese plants back to Paris. His movements were limited, and sometimes when he did get to travel out of the city it was the wrong season for plant collection. Later collections were lost by shipwreck or captured by the British.(8) As the story goes, d’Incarville eventually gained favor and greater freedom to collect Chinese plants by supplying the Emperor with a specimen of Mimosa sensitiva, which was greatly admired.(9)

After so may problems with ocean transport, d’Incarville took to sending his letters and botanical packets overland via the regular caravans that trekked through Mongolia and Siberia to Moscow. By this route, in 1747, the seeds of the Pagoda tree made their plodding way from Peking to Moscow, and thence to Bernard de Jussieu, Professor of Botany at the Jardin du Roi in Paris.(10) Strangely, not all of the materials d’Incarville forwarded out of China were studied immediately; some of the samples languished in Paris for 140 years before they were eventually examined and cataloged.(11)

Fortunately, the Pagoda tree seeds were among the d’Incarville discoveries that were studied soon after they were received, along with other important finds including Ailanthus altissima (Tree of Heaven) and Koelreuteria paniculata (Goldenrain tree). Seeds of Styphnolobium japonicum were planted near Paris, and the tree was nurtured until it first flowered in 1779, when its genus could be determined.(12) Seeds were also distributed to other botanical centers in Europe and were introduced to Kew Gardens in London by James Gordon in 1753.(13)

Writing in 1921, W. J. Bean described the current size of two of the earliest Western specimens that were sill living at that time. The first, planted at Kew in 1760, had a trunk 13 ft. in circumference and was held together with guy wires and cabling. Another, at the Old Botanic Garden at the Schoenbrunn near Vienna, had a height of 70 feet and a spread of 105 feet, with a trunk circumference of 18 feet.(14)

Description

The tree that d’Incarville brought to the attention of the Western world was classed as a member of the legume family, and was initially assigned to the genus Sophora, which is an Arabian word for a tree with pea-shaped flowers.(15) Its flowers are indeed one of its most notable features. Lightly fragrant, pale, creamy yellow to greenish-white, and about 1/2 inch long, they cover the tree in abundant pyramid-shaped terminal panicles up to 12 inches across.(16) They are all the more valuable as this is one of the last of the large ornamental trees to bloom in the north,(17) usually over several weeks from the end of July well into August.(18)

The flowers are followed by clusters of leguminous pods that range from 2 to 4 inches long, containing 1 to 6 seeds.(19) Each pod is constricted between the individual seeds in a way that resembles a string of beads.(20) In the fall, the light-green pods make a delicate filigree against the dark green leaves, and after the leaves drop, the pods turn olive green and linger on the tree, sometimes remaining throughout the winter.(21)

The Pagoda tree’s leaves are pinnately compound, 6-10 inches long, composed of 7 to 17 ovate leaflets, each 1-2 inches long and about half as wide. The leaves are deep green and lustrous above and glaucous pale green beneath.(22) The bright green leaf color lasts well into the fall (to mid-November in the Boston area), when the leaves turn yellow very briefly and drop almost immediately.(23)

The young stems are slender, with prominently protruding nodes (24) and smooth gray-green bark which provides some winter interest.(25) The bark of mature trunks and branches is gray and corrugated.(26)

The Pagoda tree usually has an upright spreading habit and a broadly rounded open crown, although this can vary greatly. William Flemer of Princeton Nurseries reports that “seedling-grown sophoras are among the most variable trees. One seed lot can produce a variety of forms–from weeping to quite upright.”(27) Older trees can develop a broadly-spreading vase-shaped form.

Moderately fast-growing, the Pagoda tree eventually reaches 50 to 75 feet in height with a comparable spread.(28) It casts a dense shade when young, but a more open shade as it matures.(29)

The Pagoda tree is subject to very few disease or insect problems. William Flemer states positively that it “does not suffer from foliar diseases, leaf-eating insects or spider mites.”(30) He does admit to observing some leafhopper damage among young trees in the nursery, but not in larger established trees. Individuals growing in the northern zones (4-5) can be subject to twig blight and stem canker due to winter injury.(31)

Although somewhat susceptible to cold and drought when young, once established, the Pagoda tree is tolerant of pollution, heat and drought.(32) It does best in sun to part shade in a loamy, well-drained soil,(33) but also grows well in high pH soils,(34) and is widely adaptable throughout USDA zones 4 to 8.(35,36) As a legume, its ability to fix nitrogen through rhizobial symbiosis allows it to thrive even on sterile soils.(37)

It has taken some time, however, for these many positive characteristics to become appreciated, and the history of the Pagoda tree in the United States has been a story of misunderstanding and neglect.

Introduction to North America

The first record of the Pagoda tree in the United States appears (under its earlier name Sophora japonica) in the 1811 catalog of the Elgin Botanic Garden in New York City.(38) This first botanic garden in the United States was founded by Dr. David Hosack in 1801 on the future site of Rockefeller Center. A Columbia College professor, Dr. Hosack was a botanist and traveler as well as a physician. (An interesting side note is that Dr. Hosack was the physician who attended Alexander Hamilton in his fatal duel with Aaron Burr.) (39) The medicine of the time strongly depended on natural plant remedies, and the new plants that were being discovered in voyages of exploration were exciting the medical world with their possibilities as a source for new medicines. Dr. Hosack acquired a tract of rough pasture land, part of the common lands north of 26th Street, to serve both as a garden for medicinal plants and a pleasure ground for the city residents.(40)

Unfortunately for Dr. Hosack’s vision, the relentless march of the city northward doomed his garden almost before it had begun. By 1811, the land’s enormous increase in value (to $75,000) had increased the tax assessments to the point where Hosack was forced to sell the land to the city. For a few years the garden was maintained by the College of Physicians and Surgeons, but the city continued to grow around it, and by Hosack’s death in 1835, he knew his garden was doomed.(42)

The records show that the Sophora japonica that grew in the Elgin Botanic Garden was grown as a greenhouse plant.(42) Most of the contacts with China up to that time had been with the southern ports of Canton, with its subtropical climate, so in the absence of any definitive information, new plants from China were assumed to be tender.(43) As we now know, this was an unnecessary precaution, as Sophora japonica/Styphnolobium japonicum is really quite hardy.

Around the same time, Sophora japonica also found its way into the collection of two Quaker farmers in Pennsylvania. Samuel and Joshua Pierce had begun a collection of exotic trees at their farm near Kennett Square in 1798.(44) We don’t know exactly where they obtained their Sophora and exactly when it was planted, but we do know that it was growing on the grounds in 1853, when Pierre Samuel duPont purchased the land to save the Pierces’ arboretum and to begin the development of Longwood Gardens. This early tree, which may be the oldest Pagoda tree growing in the United States, still remains in the Longwood Gardens collection (45) and was measured in 1970 to have a trunk circumference of 13 feet 7 inches. (46)

The 19th century

Several American books on landscaping that appeared in the late 19th century mentioned Sophora japonica favorably, but acknowledged that it was not very commonly used in American gardens. In the earliest of these, A Treatise on the Theory and Practice of Landscape Gardening, which was first published in 1841, Andrew Downing apparently classed Sophora japonica as a shrub, rather than a tree. In his 1875 update of the Downing book, Henry Winthrop Sargent, corrects this impression, attributing the mistake to the fact that “there is not to our knowledge, any large tree of it in this country”.(47)

In his 1870 book, The Art of Beautifying Suburban Home Grounds of Small Extent, Frank J. Scott summarizes what will be the story of Sophora japonica for the next century:

Considering the delicacy of its foliage, its purity and depth of color, and the hardiness of the tree, it is curious that so few fine specimens of this tree are yet to be seen in this country. … We have heard of no large specimens in this country. … The peculiar tone of its foliage is a deep velvety green that is unequaled by any deciduous tree we know of. … The leaves are among the last to surrender to autumn frosts, and turn to a yellowish-green before they fall. (48)

Sargent, too, praised its foliage and pointed out its suitability to the warm summers of the United States:

It is quite distinctive in winter by the dark green bark of its young wood; and in summer by the dark blue green of its foliage…. It grows rapidly and is peculiarly adapted to the United States from one remarkable property of its foliage, which is the power it has to retain both its leaves and their color in the very hottest and driest seasons, when locusts and acacias and other pinnate leaved leguminaceae are apt to lose their foliage.(49)

Interestingly enough, Sargent failed to note an additional advantage conferred by the warm U.S. summers—the fact that warm weather greatly advances the Pagoda tree’s age at first flowering. In England, the Pagoda tree often did not flower until thirty or forty years of age, and in wet, cold summers, blossoms often did not develop at all. (50) In contrast, Pagoda trees grown in the Eastern United States usually flower at 10 to 12 years of age, (51) and Michael Dirr has attributed this to the warmer summers, particularly to the warm summer nights, of this region. (52) But his difference was not recognized until recently; reading English sources, such as W. J. Bean’s Trees and Shrubs Hardy in the British Isles, would have given misleading information about the tree’s behavior in the United States.

Varieties

The weeping form of the Pagoda tree was particularly suited to the picturesque tastes of the Victorian era, and was more commonly used than the species during that period. Styphnolobium japonicum ‘Pendula’ had first been cultivated in China; the plant-hunger Robert Fortune reported seeing a weeping Pagoda tree in Shanghai during his visit to that city in 1853. (53) Although it seldom flowers, (54) and is difficult to propagate and expensive, Scott called this variety:

the finest of small pendulous trees. … [Its] branches are green and somewhat angular or crooked so that in winter the tree has a somewhat knotted and curious look. … It is at the same time symmetrical and picturesque. (55)

Sargent praised it as well:

It has long pendulous shoot … We hardly know anything more ornamental or striking; even in winter, the long slender branches of beautiful bright green render it most attractive. (56)

‘Pendula’ is still used today as a formal specimen or living sculpture. Its convoluted branching structure makes very little growth on its own, so it must be grafted to seedling understock at the desired ultimate height of the resulting tree.(57)

Another early variety, ‘Violacea’, is apparently no longer available in the nursery trade, although it is grown at the Arnold Arboretum. Brought from China to the Paris Jardin des Plantes in the 1850s, this variant was described as having flowers “stained with rose-violet”.(59) Although the flowers may have been beautiful, it bloomed too late to open well. (60) and may have been given up because its flowering was unreliable.

A third variety, ‘Variegata’, was soundly disliked by all who wrote about it, and is also no longer available. Sargent wrote, “The color of the leaf is sickly and we do not consider it desirable, except for arboretums.” (61)

A variety that can still be found is ‘Tortuosa’, (62) which is marked by twisted branching and very slow growth.(63)

The 20th century

The general public’s ignorance of the Pagoda tree continued through most of the 20th century. In their fall 1928 catalog, the R and J Farquhar nursery company inaccurately described Sophora japonica as a dwarf tree, and did not list it at all in their 1931 catalog.(64)

In 1940, Marian Cruger Coffin wrote in Trees and Shrubs for Landscape Effects:

True summer flowering trees are rare, so it is surprising that the charming Japanese Pagoda Tree … is not more employed as a garden accent at that season. (65)

In Arnoldia’s list of “Forty-five of the Best Trees for Massachusetts Gardens” published in 1952, the same theme was sounded:

A desirable large tree, it should be used considerably more than it is. (66)

And as recently as 1990, Michael Dirr wrote in his Manual of Woody Landscape Plants:

A very distinction and aesthetically handsome tree in flower; should be used more extensively.

So although the Pagoda tree was often recommended in landscaping guides published throughout the 20th century, it was not generally used and could be found only in the specialized collections of botanical gardens, such as the New York Botanical Garden, (67) the Arnold Arboretum, (68) Longwood Gardens, and Mt. Auburn Cemetery, as well as at some large private estates, such as Chateau-sur-Mer and Rosecliff in Newport, Rhode Island. (69) But in recent years, the situation has been changing.

In the late 20th century, as urban conditions of compacted soil, air pollution, road salt, limited root runs, and hot, dry conditions make tree survival in the city increasingly problematic, landscape architects are beginning to search out tree species that are adapted to living under such conditions. The Pagoda tree is one such species, although it has some features that make it less useful as a street tree. The main problem is its great variability in habit, with a tendency for low floppy branches that interfere with pedestrian and vehicular traffic. In addition, the species, although moderately fast growing overall, tends to be a bit slower growing when young. As, as already noted, the Pagoda tree usually does not flower until 10 or 12 years of age.

One development that is changing the situation is the introduction of new and improved cultivars, such as ‘Regent’ and ‘Princeton Upright’, which overcome many of these problems. The ‘Regent’ cultivar (Plant Patent 2338, January 7, 1964) was developed by William Flemer at Princeton Nurseries, and was selected to have a symmetric, upright growth habit, a fast growth rate when young, and an early flowering age (6-8 years), which still retaining all of the toughness and pollution-resistance of the species. (70)

One remaining drawback to the Pagoda tree’s use as a street tree is its “messiness factor”–the fact that it drops flowers, leaves, twigs, and pods at different times of the year. How much of a drawback this is can be a matter of personal opinion. Some might see the falling blossoms as a mess; others describe them as creating “a creamy carpet under the tree”. (71) The leaves may be small enough that they do not create a significant disposal problem. (72)

Notwithstanding the potential inconvenience of its somewhat untidy habits, the Pagoda tree is a tree of great beauty that can thrive in the poorest of conditions. The recent University of Massachusetts publication Planting and Maintaining Sustainable Landscapes features the Pagoda tree in its list of recommended low maintenance plants, (73) and William Flemer recommended it for use in highway median strip planting. (74) It is also highly praised in the Garden Club of America’s book, Plants that Merit Attention, Volume 1 – Trees:

Distinctively beautiful; one of the most outstanding of the leguminous trees. Showy, late summer bloom of yellowish pea-like flower; leaves remain green late in fall. Lovely shape creates a handsome shade tree. Important plus: can withstand city conditions … valued as a specimen residential tree. (75)

The Pagoda tree is turning up today in many difficult places: in cramped locations in our largest cities, (76) shading a Bethlehem Steel parking lot, (77) standing in for the lost elms in the recent renovation of Harvard Yard, admired by Christopher Lloyd in Oehme and Van Sweden’s innovative city garden at the Federal Reserve Building in Washington, D.C. (78) and lining the urban streets of Cambridge and Watertown. As long as we live in cities, we should look to the Pagoda tree to provide an oasis of green and a cascade of fragrant flowers on a hot summer day.

Footnotes

1. Shanghai Lexicon Publishing House
2. Jacobson, p. 68
3. Sargent, p. 96
4. Lu, p. 29
5. Shanghai Lexicon Publishing House
6. Coats, p. 89
7. Coats, p. 90
8. Coats, p. 90
9. Coats, p. 90
10. Bretschneider, p. 46
11. Coats, p. 90
12. Bretschneider, p. 48
13. Bretschneider, p. 138
14. Bean, p. 520
15. Poor
16. Poor
17. Dirr, p. 792
18. Flemer, “Field Notes”
19. Poor
20. Flint, p. 526
21. Poor
22. Dirr, p. 791
23. Flemer, “Field Notes”
24. Flemer, “Field Notes”
25. Flint, p. 526
26. Flemer, “Field Notes”
27. Flemer, “Field Notes”
28. Dirr, P. 791
29. Poor
30. Flemer, “Field Notes”
31. Flint, p. 526
32. Dirr, p. 791
33. Poor
34. Flemer, “Field Notes”
35. Dirr, p. 791
36. Flemer, “Field Notes”
37. Jacobson, p. 68
38. Rehder, p. 25
39. Andrews
40. Andrews
41. Andrews
42. Rehder, p. 25
43. Spongberg, p. 94
44. Spraker, p. 40
45. Tetter
46. Spraker, p. 40
47. Downing/Sargent, p. 466
48. Scott, p. 393
49. Downing/Sargent, p. 466
50. Bean, p. 520
51. Poor
52. Dirr, p. 792
53. Bretschneider, p. 451
54. Hudak, p. 201
55. Scott, p. 393
56. Downing/Sargent, p. 467
57. Flemer, “Field Notes”
58. Flemer, “Field Notes”
59. Bean, p. 520
60. Bean, p. 520
61. Downing/Sargent, p. 467
62. Isaacson, p. 195
63. Hudak, p. 201
64. Farquhar catalog
65. Coffin, p. 6
66. “Forty-five of the Best Trees…”, Arnoldia
67. “List of Plants on the Grounds”, Bulletin of the New York Botanical Garden
68. Spongberg, p. 94
69. Champlin
70. Flint, p. 526
71. Dirr, p. 792
72. Flemer, “Field Notes”
73. Clark, p. 9
74. Flemer, “Island and Median Strip Planting”
75. Poor
76. Flemer, “Field Notes”
77. Frederick, p. 37
78. Lloyd

Bibliogaphy

Andrews, Kenneth, Dr. Hosack’s Garden. New York: Rockefeller Center, 1938.

Bailey, Liberty Hyde and Bailey, Ethel Zoe. Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada. Rev. and exp. by the Staff of the Liberty Hyde Bailey horatorium, Cornell University, New York: MacMillan Publishing Co., Inc., 1976.

Bean, W. J. Trees and Shrubs Hardy in the British Isles. 3rd ed. London: John Murray, 1921.

Bretschneider, E. M. D. History of European Botanical Discoveries in China. Reprint of 1898 ed. Leipzig: Zentral-Antiquariat der Deutschen Demokratischen Repubik, 1981.

Bunch, Ida Hay. “Summer Bloom in the Arnold Arboretum”. Arnoldia 38[3] (May/June 1978): 112.

Champlin, Richard L. Trees of Newport. Newport R.I.: The Preservation Society of Newport County, 1976.

Clark, William F., and Clark, Roberta A. Planting and Maintaining Sustainable Landscapes. University of Massachusetts.

Coats, Alice M. The Quest for Plants. London: Studio Vista, 1969.

Coffin, Marian Cruger. Trees and Shrubs for Landscape Effects. New York: Charles Scribner’s Sons, 1940.

Crockett, James Underwood. Trees. New York: Time-Life Books, 1972.

Dirr, Michael A. Manual of Woody Landscape Plants, 4th ed. Champaign IL: Stipes Publishing Co., 1990

Downing, Andrew Jackson. A Treatise on the Theory and Practice of Landscape Gardening. 9th ed., rev. and enl. by Henry Winthrop Sargent, 1895. Sakonnet R.I.: Theophrastus, 1977.

Farquhar, R & J Co. Nursery catalogs. Boston, 1928 and 1931.

Flemer, William, III. “Field Notes on Sophora japonica”. American Nurseryman 176(9):114 1 November, 1992.

Flemer, William, III. “Island and Median Strip Planting”. Arnoldia 44[4] (Fall 1984): 20.

Flint, Harrison I., Landscape Plants for Eastern North America. New York: John Wiley, 1983.

“Forty-five of the Best Trees for Massachusetts Gardens”. Arnoldia 121 (March 7, 1952): 18.

Frederick, William H. Jr. 100 Great Garden Plants. New York: Alfred A. Knopf, 1975.

Hobhouse, Penelope. Plants in Garden History. London: Pavilion Books, 1992.

Hudak, Joseph. Trees for Every Purpose. New York: McGraw Hill, 1980.

Isaacson, Richard T. Andersen Horticultural Library’s Source List of Plants and Seeds. Minnesota: Andersen Horticultural library, 1989.

Jacobson, Arther Lee. Trees of Seattle. Seattle: Sasquatch Books, 1989.

Koller, Gary L., and Dirr, Michael A. “Street Trees for Home and Municipal Landscapes”. Arnoldia 39[3]: 131-32.

Li, Hui-Lin. The Origin and Cultivation of Shade and Ornamental Trees. Philadelphia: University of Pennsylvania Press, 1963.

“List of Plants in the Grounds”. Bulletin of the New York Botanical Garden. 1[3]:137.

Lloyd, Christopher. “What I Found in America”. Horticulture, May 1986, p. 20-25.

Poor, Janet M., ed., The Garden Club of America. Plants That Merit Attention, Volume 1 – Trees. Portland: Timber Press, 1984.

Rehder, Alfred. “On the History of the Introduction of Woody Plants into North America”. Arnoldia, Winter 1991, p. 25.

Sargent, Charles Sprague, ed. Plantae Wilsonianae. Reprint of 1916 edition. Portland: Dioscorides Press, 1988.

Scott, Frank J. The Art of Beautifying Suburban Home Grounds of Small Extent. New York: D. Appleton and Co., 1870.

Shanghai Lexicon Publishing House. Encyclopedia. Shanghai: 1979. “Huái Shù” entry translated for me by native Chinese speaker Jing Wang.

Spongberg, Stephen A. A Reunion of Trees. Cambridge: Harvard University Press, 1990.

Speaker, Leslie. Tulip Trees and Quaker Gentlemen: 19th Century Horticulture at Longwood Gardens. Kennett Square PA: Longwood Gardens Inc., 1975.

Teeter, Enola, Librarian, Longwood Gardens. Telephone conversation, Nov. 7, 1995.

Walheim, Lance, ed. The World of Trees. San Francisco: Ortho Books, 1977.

Wyman, Donald. Trees for American Gardens. 3rd ed. New York: Macmillan Publishing Company, 1990.

Additional notes from instructors

There is a tree at least 150 years old, brought back by a sea captain, in Edgartown MA, on the main street of the town.

This tree is highly resistant to mechanical damage to the trunk!

Used extensively as street tree in Paris

Tree has been planted as a street tree in Boston – see 20-30 yr. old specimens in Boston’s South End

Also it’s a nice alternative to the honeylocust which is overplanted.

Links

The Portuguese blog Dias com árvores (Days with trees) posts some photos of the pagoda tree in the Jardin des Plantes in Paris and the Forbidden City in Beijing.

Leslie Turek