Поспєлов, С. В. “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”. Scientific Progress & Innovations, no. 3, Sept. 2012, pp. 35-43, doi:10.31210/visnyk2012.03.07.