The goldenrain tree (Koelreuteria paniculata) is native to eastern Asia, but is a familiar street tree in much of the United States. Landscape architects and planners are wont to like trees for their convenience without much regard for ecological considerations. The golden rain tree tolerates air pollution well and doesn’t get very big, topping out at about 40 or 50 feet high with a canopy about the same width.
It has aesthetic features going for it as well. Its flowers are yellow and showy, hanging from panicles at the end of the branches all over the crown. They are also arrive in June or July, well ofter most other trees are finished flowering. Horticulturally minded planners with an affection for gardening will remember that one of the rules for attractive perennial beds is to have a variety of species that flower in waves through the season. This principle will be in the back of their minds as they tell a public official that after the basswoods and Bradford pears are done, it will be delightful to have another street tree burst into bloom and brighten up the urban streetscape.
The seed pods that form in the place of the pollinated flowers are nearly as attractive as the blooms. While the individual flowers have four long, thin floppy petals with yellow stamens sticking out past the petals, the seed pods look like minature Chinese lanterns, their papery walls flushed with gold tinged with pink. The leaves at compound pinnate (like an ash); each leaflet edged with rough teeth.
While all of the above looks quite attractive on the tree, we are talking about a deciduous tree here, so in late October you have quite a mess on the sidewalk under every tree. More financially conservative planners would be sure to veto its planting, as they would be thinking of paying for the man-hours required for clean-up each autumn.
But the goldenrain tree has been a popular landscape tree in the United States since the early 19th century. None other than Thomas Jefferson helped to introduce to this continent. In 1809 Jefferson received seeds from a French friend Madame de Tessé. Two years later he reported in a letter to de Tessé that the seeds had successfully germinated. The tree is now “naturalized” on the grounds of Monticello.
How did Madame de Tessé get her goldenrain trees? French Jesuit Pierre d’Incarville sent seeds back to France from China in the mid 18th century and by 1763 they were reported to be established in the Jardin du Roi in Paris. There are also reports of them being grown as early as the 16th century in England.
Scottish industrialist William Maclure, Robert Owen’s financial partner in the founding of New Harmony, Indiana in 1824, imported goldenrain trees (presumably from Great Britain) and planted them around his house in the utopian community. The social experiment lasted only two years, but the trees persisted so that over a hundred years later they would make enough off an impression on Ross Lockridge, Jr. that he would name is Great American Novel Rain Tree County.
Lockridge, the son and namesake of a prominent Indiana historian, traveled all over the state with his father. Lockridge Sr. gave recitations at historical sites that imparted local history to the residents. They visited New Harmony several times. After its failure as a social experiment it continued on as a hotbed of scientific research, particularly geology, until just before the Civil War.
New Harmony is in the southwest corner of Indiana in Posey County. As at Monticello Maclure’s goldenrain trees had naturalized and spread into the natural landscape, so much so that the area received the nickname “Rain Tree County,” which Lockride adopted for his 1948 novel (later made into a movie starring Liz Taylor and Montgomery Clift).
But the “naturalizing” ability of K. paniculata has led to it being regarded as a pest and invasive in some parts of its introduced range. It is described as naturalized in Florida, Alabama, Lousiana, and Texas, which suggests that it prefers the warmer climate. In fact, it is more tolerant of warmth than some natives and therefore outcompetes them in the wild.