The dry, brown pods of the savonnier trees rattle in the breeze, in a quiet side street off rue du Faubourg St Denis.

Koelreutia paniculata is a species well adapted to life in the Paris streets.  The trees can’t stand much frost but they are resistant to summer heat and drought.   The leaves look rather like those of an ash tree; the dangling panicles of yellow flowers in mid summer are more distinctive.  In winter, when the yellow, autumn leaves have fallen, the twisting pattern of the branches and the persistent seed pods are revealed.

Although the French name, savonnier, means soap tree, it’s not this species but a close relative, Sapindus mukorossi, that produces the seeds known as soap nuts.  Various websites claim that you can make soap from the bark of the savonnier, but that may be another case of mistaken identity.