V. V.  Protopopova and Tkachenko, V. S., ?Istoriya ta prohnoz poshyrennya Grindelia squarrosa (Pursh) Dunal. (History and prognosis of Grindelia squarrosa (Pursh) Dunal distribution.) Ukr?, Bot. Zhurn, no. 5, pp. 457 - 461, 1979.