The first findings of invasive Reynoutria ×bohemica Chrtek & Chrtková (Polygonaceae) in Latvia

The knotweed genus Reynoutria is of Asian origin with only five known species. Due to human activities, two species Reynoutria japonica and Reynoutria sachalinensis have spread beyond their natural range in Europe, North America, Australia and New Zealand. In their adventitious range, these two species hybridised, resulting in the hybrid species Reynoutria ×bohemica, which is much more expansive than both parent species. In some regions this hybrid species is not yet recognized and is usually misidentified. Given that each Reynoutria species has a different degree of invasiveness, and that, as a result of climate change, their invasiveness is also increasing, it is important to correctly identify each particular species. The hybrid species was not recognized in Latvia until now. In this study, records of R. ×bohemica were found in eight localities in Latvia (in Dobele city and surroundings, and Jelgava city, with the first record dating back to 2019). These are the first records of R. ×bohemica in the Baltic countries as well. More detailed surveys of stands of Reynoutria species and risk assessments of R. ×bohemica invasiveness in Latvia and neighbouring countries should be conducted in the nearest future. Morphological features allowing distinguishing similar species, R. ×bohemica and R. japonica, were discussed further.