The first findings of invasive Reynoutria xbohemica Chrtek & Chrtkova (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 xbohemica, 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. xbohemica 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. xbohemica in the Baltic countries as well. . More detailed surveys of stands of Reynoutria species and risk assessments of R. xbohemica invasiveness in Latvia and neighbouring countries should be conducted in the nearest future. Morphological features allowing distinguishing similar species, R. xbohemica and R. japonica, were discussed further.

Automated summary

The Reynoutria genus, originating from Asia, includes only five known species. Due to human activities, two species, Reynoutria japonica and Reynoutria sachalinensis, have spread beyond their natural range to Europe, North America, Australia, and New Zealand. Hybridization of these two species has resulted in the more aggressive hybrid species Reynoutria xbohemica, which is misidentified in some regions. Proper identification of each species is crucial due to their varying invasiveness and increasing impact from climate change. Discovery of Reynoutria xbohemica in Latvia, with the first records in Baltic countries, calls for further research and risk assessments.