D. J. Metcalfe, "Hedera helix L." Journal of Ecology 93 (2005), 632–648; cited in The Ivy Files (页面存档备份,存于互联网档案馆) (City of Portland website; last accessed 16 March 2014)
D. J. Metcalfe, "Hedera helix L." Journal of Ecology 93 (2005), 632–648; cited in The Ivy Files (页面存档备份,存于互联网档案馆) (City of Portland website; last accessed 16 March 2014)