Sennikov, A. N., and A. Kurtto. “The Taxonomy and Invasion Status Assessment of Erigeron Annuus s.L. (Asteraceae) in East Fennoscandia”. Memoranda Societatis Pro Fauna Et Flora Fennica, Vol. 95, Jan. 2019, pp. 40-59, https://journal.fi/msff/article/view/79497.