"AGM Plants - Ornamental"(PDF). Royal Horticultural Society. July 2017. p. 59. Archived(PDF) from the original on 5 January 2018. Retrieved 21 March 2018.
"AGM Plants - Ornamental"(PDF). Royal Horticultural Society. July 2017. p. 59. Archived(PDF) from the original on 5 January 2018. Retrieved 21 March 2018.