First evidence for the presence of invasive Solidago altissima (Asteraceae) in Europe.
The North American invasive species Solidago altissima L. (Asteraceae) is reliably recorded from a single locality in Belgium (Beveren, Waaslandhaven, Verrebroekse Plassen). Nuclear genome size, as measured by flow cytometry, showed this population to be distinct from the closely similar and widespread S. canadensis L. Plants were shown to be hexaploids, with an estimated chromosome number of 2n=54, while only diploids (2n=18) of S. canadensis are known from Europe. These findings were further supported by morphological traits. Solidago altissima has repeatedly been claimed from Europe but all these records may be referable to S. canadensis var. canadensis and, more likely, S. canadensis var. hargeri Fernald. To the best of our knowledge, the recently detected population in Belgium represents the first unequivocal record of S. altissima in Europe.