This tree is unforgettable if you see it in October when the tree undergoes the shedding of its very abundant golden-yellow pollen. That is how this tree got its name: when it sheds its pollen (over several weeks time), the ground beneath the tree is quite yellow and looks like gold dust has “rained down” from the tree. Three species are known, and the one shown here is Koelreuteria bipinnata = the “Golden Rain Tree.”
Figure 1. Golden rain tree in Santa Clarita, Southern California.
Koelreuteria is native to China, Korea, and Outer Mongonlia (i.e., in both Russia and Mongolia). It has been was cultivated in Japan since at least the 1200’s, and it was introduced to Europe in 1747 and to North America is 1763. It is supposedly now a popular landscape tree worldwide. It is drought-tolerant (once it is well rooted). It is a moderately hardy tree. I had never seen one the until Fall of 2025, when I spotted, in a local municipal park, a 40-foot-tall tree with “clumps” of golden pollen.
The leaves of this fast-growing tree are bipinnate. The leaves have serrated margins, and the tree branches have clusters of small golden-yellow flowers. Also present are numerous, pink/red, paper-thin parchment-thin (lantern like) seed pods (each pod containing two small black seeds). With ripening, these fragile pods lose most of their color, become brownish pink (see Figure 3) and eventually fall off the tree.
Classification
Kingdom Plantar
Clades (4 of them)
Order Sapindales
Famly Sapindaceae
Genus Koelreuteria
Type species K. paniculata
The oldest know fossil of Koelreuteria (fruit valves) is from the Paleocene of southern Russia (Ablaev, 2000). Fossil fruits of this genus have also been found from middle Eocene deposits of the Green River Formation and Eocene deposits of British Columbia (see Wikipedia, 2025). Also found in the upper Eocene (about 34 million years old) Florissant Fossil Beds National Monument (see National Park Service Website nps.gov for some images of fossils (including a fossil plant from the Florissant Fossil Beds).
The species shown here is K. bipinnata. For images of the other two living species, see the website listed below.
Figure 1. Golden Tree in the process of shedding its "golden" pollen.
Figure 2. Seed pods (red color) of the Golden Tree.
Figure 3. Various parts of the Golden Tree: leaves, dried-out seed pods (in the previous figure these seed pods
were red, but a few months later = when this additional figure was taken, the red color had gone), and some other small-red flowers still
attached to their thin stems.
References
Ablaev, A. G. 2000. Paleogene biostratigraphy of the coastal region in south Primorye. Vladivostok: Dal’nauka [in Russian].
https://www.youtube.com/watch?v=ttRU1-dlMR8
National Park Service Website nps.gov
Wikipedia 2025
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