С. В. Поспєлов, “Peculiarities of development of inflorescences and flowering of purple coneflower (Echinacea purpurea (L.) Moench) and pale coneflower (Echinacea pallida (Nutt.) Nutt.) in the foreststeppe of Ukraine”, Scient.Prog.&Innov., no. 3, pp. 35–43, Sep. 2012.