Dittrichia graveolens (Asteraceae), rapidly spreading along European highways, recorded in Lithuania

Abstract

For a long time, railways were the main pathway for the accidental introduction of alien plant species, but now highways and other roads are becoming increasingly important in this process. Considering that Dittrichia graveolens is spreading rapidly along highways in Central Europe and neighbouring Poland, a targeted search was conducted in Lithuania in 2023. Dittrichia graveolens was recorded at two sites along the Kalvarija–Kaunas highway (Kazlų Rūda district, in the environs of Pentupiai, and Kaunas city, in the environs of Jonučiai). At both sites, the species occupied relatively compact stands consisting of several hundred individuals, suggesting that the stands were formed from locally matured seeds. The mean number of flowers per capitulum in Lithuania in 2023 was 20.5 ± 4.9, and the realised fecundity was 89.7% of the potential fecundity. It is presumed that the seeds of Dittrichia graveolens were accidentally introduced into Lithuania by trucks, probably attached to tyres. Currently, this species is classified as a casual alien, but its naturalisation is expected. The study revealed that the first record of Dittrichia graveolens in Poland was not in 2013, as previously reported, but more than 20 years earlier, in 1990, near Kraków, at the slag deposit site of the Nowa Huta Steelworks.