SSR markers distinguish critically endangered Acer campestre populations from cryptic invading gene pools

Garden escapes of Acer campestre spread as a cryptic invading gene pools and challenge the conservation of a unique ancient population in southern Scandinavia. The native gene pool consists of just 34 individuals and is listed as critically endangered. This population is more than 150 years old and represents a unique diorama into an almost extinct genetic diversity of the early 19th century. That the native individuals cannot be separated from the introduced by morphology makes it impossible to delimit populations worthy of conservation. Genetic structuring was based on six SSR markers and reveals that, although the native population is small, it does not suffer from inbreeding. This article reports a high group affinity (Q coefficient) of the known native gene pool and a new finding of a population not earlier identified as native. Because the population is old and the fruit set is strongly reduced, it is recommended to preserve the genetic material by ex situ grafting and introduction of carefully chosen individuals from related gene pools.