We have information from several sources:
A Review of the Taxonomy of the Genus Echinacea—Kathleen A. McKeown
Assembling and Characterizing a Comprehensive Echinacea Germplasm Collection—Mark P. Widrlechner and Kathleen A. McKeown
Echinacea angustifolia: An Emerging Medicinal—Ali O. Sari, Mario R. Morales and James E. Simon
Cichoric Acid and Isobutylamide Content in Echinacea purpurea as Influenced by Flower Developmental Stages—W. Letchamo, J. Livesey, T.J. Arnason, C. Bergeron, and V.S. Krutilina
Factors Affecting Echinacea Quality—W. Letchamo, L.V. Polydeonny, N.O. Gladisheva, T.J. Arnason, J. Livesey, and D.V.C. Awang
The Use of RAPDs for Assessment of Identity, Diversity, and Quality of Echinacea—J. Kapteyn and J.E. Simon
In Vitro Regeneration and Agrobacterium Transformation of Echinacea purpurea Leaf Explants—A. Koroch, J. Kapteyn, H.R. Juliani, and J.E. Simon
Immune Stimulants and Antiviral Botanicals: Echinacea and Ginseng—Dennis V.C. Awang
Phytomedicines as a New Crop Opportunity—Loren D. Israelsen
The Herb Hunters Guide—Sievers, A.F. 1930.
Outside links:
Echinacea Southern Crop Protection and Food Research Centre Agriculture & Agri-Food Canada