This study examines patterns of morphological similarity within Hedera (the ivy genus, Araliaceae). Both cluster and principal components analyses reveal two major groupings corresponding to species of Hedera with stellate and scale-like trichomes. Characters traditionally used to delimit members of the genus were evaluated. Morphometric analyses found that the major delimiting characters for taxa with scale-like trichomes are: 1) number of leaf lobes, 2) length of the middle leaf lobe, 3) ratio of trichome center diameter to overall size, and 4) overall width of the leaf. The major delimiting characters for taxa with stellate trichomes are: 1) degree of leaf sinus shallowness, 2) length of leaf lobes, 3) width of the leaf middle lobe, 4) number of leaf lobes, and 5) trichome position. The newly described Hedera maderensis K. Koch ex Rutherford subsp. McAllister is highly distinct morphologically from the typical subspecies, confirming evidence from chloroplast and nuclear ribosomal DNA data that suggest an independent origin of the two taxa. Hedera iberica (McAllister) Ackerfield & J. Wen is recognized at the species level. A key to the taxa of Hedera is provided to aid in the identification of this complex group.