Echinacea purpurea*

Echinacea purpurea (Eastern Purple Coneflower or Purple Coneflower) is a long lasting perennial for the sunny border. Its cone-shaped flowering heads are usually, but not always purple. Most Echinacea grow from taproots, except E. purpurea, which grows from a short caudex with fibrous roots. They have erect stems that in most species are unbranched. Both the basal and cauline leaves are arranged alternately. The leaves are normally hairy with a rough texture, having uniseriate trichomes (1-4 rings of cells) but sometimes they lack hairs. The basal leaves and the lower stem leaves have petioles, and as the leaves progress up the stem the petioles often decrease in length. The leaf blades in different species may have one, three or five nerves. Some species have linear to lanceolate shaped leaves, and others have elliptic to ovate-shaped leaves; often the leaves decrease in size as they progress up the stems. Leaf bases gradually increase in width away from the petioles or the bases are rounded to heart shaped.

Although Native American tribes didn't use echinacea to prevent the common cold, some Plains tribes did use echinacea to treat some of the symptoms that could be caused by the common cold: The Kiowa used it for coughs and sore throats, the Cheyenne for sore throats, the Pawnee for headaches, and many tribes including the Lakotah used it as an analgesic.

Native Americans learned of E. angustifolia by observing elk seeking out the plants and consuming them when sick or wounded, and identified those plants as elk root.

Echinacea products that are marketed and studied in clinical trials vary widely in composition. They contain different species (E. purpurea, E. angustifolia, E. pallida), different plant segments (roots, flowers, extracts), different preparations (extracts and expressed juice), and different chemical compositions. Well-controlled clinical trials are limited, and many of them are low in quality. There are multiple scientific reviews and meta-analyses published to evaluate the peer reviewed literature on the supposed immunological effects of echinacea. However, the variability of the echinacea products used in the studies limited the comparison of effects and safety among those studies. The results are mixed, inconclusive and have not been approved for any health benefit or anti-disease activity.

The evidence that showed the effectiveness of echinacea products in treating or preventing the common cold is weak.