The invasive water primrose Ludwigia grandiflora (Michaux) Greuter & Burdet (Spermatophyta: Onagraceae) in Germany: first record and ecological risk assessment.

A population of Ludwigia grandiflora, an aquatic weed from South America, has been recorded in the North West of Germany near Leer, Lower Saxony in an old branch of the River Leda, a tributary of the River Ems. This species is new to the German flora. After an initial observation of only a few individuals in 2004, a dense growth of L. grandiflora has been observed from 2009 onwards. An ecological risk assessment, mainly based on knowledge about invasion histories in neighbouring countries, showed that this species is a threat to German biodiversity; thus, it is considered to be invasive and has been assigned to the German Black List. In accordance with nature conservation efforts, management policies are being developed by the appropriate authority to eliminate the population.