Invasions are a major threat to the biodiversity of native ecosystems. European lineages of Phragmites australis are invasive in North America, where they compete with the native subspecies and have expanded to regions previously not known to inhabit P. australis. Nonetheless, there is relatively little attention paid to the risk assessment and prevention of such cryptic invasions in China, despite the rapidly changing climate and economic globalization, which favor species trading. We compared morphological and physiological functional traits of European (EU-type) and Chinese (CN-type) reeds cultured in common gardens in Denmark and China. We found that the EU-type grown in Denmark and China had a significantly greater specific leaf area (SLA) than the CN-type, but had otherwise similar trait values as the CN-type. Our results confirmed that the EU-type performed as well in China as in Denmark, implying a high acclimation capacity of its resource-capturing traits. We suggest that careful observation and import restriction of foreign reed types are crucial for invasion risk assessment and management.