Among the list of 18 prohibited tree species issued by Hanoi under Decision 143/2026/QD-UBND is the soapberry tree because its "fruit contains toxic substances".
According to Dr. Ngo Duc Phuong, a botanist and herbal medicine expert and Director of the Institute of Traditional Vietnamese Medicine , the soapberry plant has the scientific name Sapindus mukorossi Gaertn. (or some other species in the genus Sapindus), belonging to the Sapindaceae family.
The most distinctive feature of the plant lies in its fruit peel. The peel of the soapberry fruit contains many saponins, a group of compounds that can reduce the surface tension of water and create foam when stirred or rubbed.