Chinese flame tree
Koelreuteria bipinnata Franch.
(Sapindaceae)

Koelreuteria bipinnata is a small to medium-sized tree that is native to China.  This species, while not commonly documented in the US outside of cultivation, is sparingly established in a single county in southwest Arkansas.  Koelreuteria bipinnata is capable of self-pollination and subsequent self-fertilization, and a single plant can give rise to an entire population.  This species has been observed invading into and establishing in open and wooded areas, and probably has the potential to become invasive. 
It is similar, especially during juvenility, to another species of Koelreuteria that is naturalized in Arkansas, K. paniculata (golden-rain tree).  Koelreuteria bipinnata can be distinguished from K. paniculata by its bipinnately compound leaves with entire or finely toothed leaflets, flowers with 4 petals, and elliptic-shaped fruits.  Koelreuteria paniculata has once pinnately to occasionally a few imperfectly bipinnately compound leaves with coarsely toothed to lobed leaflets, flowers with 5 petals, and conical-shaped fruits.  During juvenility, both species have bipinnately compound leaves with lobed leaflets. 
Another species of Koelreuteria that is naturalized in the southern US is K. elegans.  This species differs from K. bipinnata by its evergreen habit, tighter inflorescences, and its leaflets with very oblique bases. 
Koelreuteria bipinnata also somewhat resembles Melia azedarach (chinaberry), but can be distinguished from it by its mature leaves which have few pinnae, and leaflets that have entire or minutely toothed margins. The leaves of M. azedarach have more pinnae relative to those of K. bipinnata, and have leaflets that are coarsely toothed to shallowly lobed.

Figures for Koelreuteria bipinnata:
A-E. leaves;
F-G. flowers;
H-K. mature fruits;
L. dried fruits;
M. seeds;
N. stem with young periderm;
O-P. bark;
Q. seedlings;
R-V. spontaneous/naturalized juvenile plants;
W-BB. naturalized plants and habit;(fig. W shows autumn color).

List of Naturalized Species

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