Invasive species are characterized by the ability to spread to new areas, causing an imbalance in the new environment. They cause a number of negative impacts, which is why new thoughts emerge about their control, eradication, and general management. From genus Reynoutria in Croatia appears two species Reynoutria japonica and Reynoutria sachalinenis, which are introduced as decorative species for horticultural purposes, both originating from Asia. In the areas where these two types have been introduced, their crossing is the hybrid Reynoutria × bohemica, which is considered to come only in the new area. Because of its great resemblance to parent species, botanists have been mistakenly referred its specimens as one of the parents for decades. It is believed that the hybrid is more demanding for control of parent species, and it has been shown that it is most common in Croatia. These three species are different in shape, size and hairiness of leaf, and also they have difference in their stamens. Here, I have analysed leaves from main and secondary axis between species Reynoutria japonica and hybrid Reynoutria × bohemica, from 10 localities per taxa.. Five morphological characteristics were measured and also there were sampled flourishing branches. It was found that all measured characteristics had larger values on the hybrid. Because of their high morphological variability, leaves from seconary shouldn't be used for determination. Morphological characteristic of the heart shaped leaf , which in most cases was always positive for the hybrid, can be used in determination. Comparing the stamens it was found that hybrid Reynoutria × bohemica have longer and more developed stamens then species Reynoutria japonica, which can be used in determination between these two species.