Answers are grounded in this paper and cite their sources.
The genus Sambucus is widespread and morphologically difficult, and as a result, no taxonomic treatment to date has been entirely satisfactory. The only modern revision, by Bolli, reduced the number of recognized species worldwide from over 30 to nine. In Bolli's treatment, five taxa formerly considered to be distinct species, including S. canadensis, S. cerulea, S. peruviana, and the endemic island taxa S. maderensis and S. palmensis, were placed within S. nigra as subspecies.
No takes yet. Share an insight, caveat, or question.
Wendy L. Applequist (2015) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: