Echinacea
Echinacea purpurea is used in traditional medicine. Although commonly sold as a dietary supplement, there is insufficient scientific evidence that Echinacea products are effective or safe for improving health or treating any disease.
Description
Echinacea species are
Herbaceous plant,
drought-tolerant
growing up to in height. They grow from
, 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 leaf and cauline (stem) leaves are arranged
Alternate leaf. The leaves are normally hairy with a rough texture, having
uniseriate (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
Leaf shape leaves, and others have
Leaf shape; 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
Leaf shape. Most species have
leaf margins that are
Leaf shape, but sometimes they are
Leaf shape.
The flowers are collected together into single rounded Flower heads at the ends of long peduncles. The have crateriform to shaped involucres which are wide. The phyllary, or below the flower head, are persistent and number 15–50. The phyllaries are produced in a 2–4 series. The receptacles are hemispheric to conic. The paleae ( on the receptacles of many Asteraceae) have orange to reddish purple ends, and are longer than the disc corollas. The paleae bases partially surrounding the cypselae, and are keeled with the apical meristem abruptly constricted to Leaf shape tips. The ray florets number 8–21 and the Petal are dark purple to pale pink, white, or yellow. The tubes of the corolla are hairless or sparsely hairy, and the Leaf are spreading, reflexed, or drooping in habit and Leaf shape. The abaxial faces of the Leaf are glabrous or moderately hairy. The flower heads have typically 200–300 fertile, bisexual but some have more. The Petal are pinkish, greenish, reddish-purple or yellow and have tubes shorter than the throats. The pollen is normally yellow in most species, but usually white in E. pallida. The three or four-angled (cypselae), are tan or bicolored with a dark brown band distally. The pappi are persistent and variously crown-shaped with 0 to 4 or more prominent teeth. x = 11.
Like all Asteraceae, the flowering structure is a composite inflorescence, with rose-colored (rarely yellow or white) flower arranged in a prominent, somewhat cone-shaped head – "cone-shaped" because the petals of the outer ray florets tend to point downward (are reflexed) once the flower head opens, thus forming a cone. Plants are generally long lived, with distinctive flowers. The common name "coneflower" comes from the characteristic center "cone" at the center of the flower head.
Taxonomy
The first
Echinacea species were named by European explorers after seeing them in the forests of southeastern North America during the 18th century. The
genus Echinacea was then formally described by
Linnaeus in 1753, and this specimen as one of five species of
Rudbeckia,
Rudbeckia purpurea.
Conrad Moench subsequently reclassified it in 1794 as the separate but related genus,
Echinacea, with the single species
Echinacea purpurea, so that the botanical authority is given as (L.) Moench. In 1818,
Thomas Nuttall, using the original name, described a variety of
Rudbeckia purpurea, which he named
Rudbeckia purpurea var
serotina. In 1836,
De Candolle elevated this variety to a species in its own right, as
Echinacea serotina (Nutt.) DC, by which time four species of the genus
Echinacea were recognised.
Historically, there has been much confusion over the taxonomic treatment of the genus, largely due to the ease with which the taxa hybridize with introgression where species ranges overlap, and high morphological variation. Furthermore it was discovered that the type specimen for Echinacea purpurea (L) Moench was not the one originally described by Linnaeus, but rather that described by De Candolle as Echinacea serotina (Nutt.) DC.
Subdivision
Many taxonomic treatments of the genus
Echinacea have recorded varying numbers of subordinate
taxa, ranging between 2 and 11. One of the most widely adopted schemes was that of McGregor (1968), which included nine species, of which two,
E. angustifolia DC and
E. paradoxa (Norton) Britton, were further divided into two
cultivar. Treatments that include ten species, differ by the addition of
E. serotina (Nutt.) DC. Alternative classification include with four species and eight subspecies, and two subgenera with four species, has been proposed, based on
Plant morphology alone, but has proved controversial. This recognised
subgenus Echinacea, with the single species
E. purpurea, and subgenus
Pallida, with three species,
E. atrorubens,
E. laevigata and
E. pallida. In this scheme, other taxa are reduced to variety rank, e.g.
E. atrorubens var.
neglecta. Subsequently, McGregor's classification was preserved in the Flora of North America (2006).
DNA analysis has been applied to determine the number of Echinacea species, allowing clear distinctions among species based on chemical differences in root . The research concluded that of the 40 genetically diverse populations of Echinacea studied, there were nine to ten distinct species.
Species
Plants of the World Online gives nine accepted species, and World Flora Online gives ten:
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Echinacea angustifolia – Narrow-leaf coneflower
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Echinacea atrorubens – Topeka purple coneflower
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Echinacea laevigata – Smooth coneflower, smooth purple coneflower
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Echinacea pallida – Pale purple coneflower
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Echinacea paradoxa – Yellow coneflower, Bush's purple coneflower
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Echinacea purpurea – Purple coneflower, eastern purple coneflower
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Echinacea sanguinea – Sanguine purple coneflower
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Echinacea serotina – Narrow-leaved purple coneflower
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Echinacea simulata – Wavyleaf purple coneflower
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Echinacea tennesseensis – Tennessee coneflower
These two databases differ in their treatment of
E. serotina (Nutt.) DC. , the former considering this as a synonym of
E. purpurea and the latter as a distinct species.
Former classification
Etymology
Moench named the genus
Echinacea, from the Greek word ἐχῖνος]] (
) for
hedgehog or
sea-urchin, in recognition that in the seed stage, the cone has spiny projections.
Distribution and habitat
Echinacea is restricted to North America, east of the Rocky Mountains, and in the Atlantic drainage area, predominantly the Great Plains and central United States and adjacent areas of Canada. The genus range is from
Saskatchewan in the north to almost the Gulf of Mexico in Louisiana and Texas in the south, and from the Ohio
,
Calcareous glade and the Carolinas in the east, to the
Rocky Mountains foothills in the west.
Conservation
Natural populations of
Echinacea are threatened by over-harvesting of wild specimens for the herbal product trade and modification of their habitats by humans. Major reductions in the size of populations of
E. laevigata and
E. tennesseensis have led to their classification as endangered species.
E. tennesseensis had recovered sufficiently by 2011 that it was removed from the list.
Cultivation
Many species of
Echinacea are cultivated for commercial use, while others, notably
E. purpurea,
E. angustifolia, and
E. pallida, are grown as
in gardens. Many cultivars exist, and many of them are asexually propagated to keep them true to type.
Uses
Echinacea has long been used as a traditional medicine.
History
Echinacea angustifolia was widely used by the North American Indigenous peoples as folk medicine, with archaeological evidence dating back to the 18th century. Traditional use included external application (insect bites, burns, wounds), chewing of roots (throat and tooth infections) and internal use (cough, pain, snake bites, stomach cramps). Some
Plains tribes used
Echinacea for cold symptoms. The
Kiowa used it for coughs and sore throats, the
Cheyenne for sore throats, the
Pawnee people for headaches, and many tribes, including the
Lakota people, used it as a
analgesic. Early European settlers noticed this and began to develop their own uses. According to
Wallace Sampson, its modern use for the
common cold began when a Swiss herbal supplement maker was told that
Echinacea was used for cold prevention by Native American tribes who lived in the area of
South Dakota. The first preparation was Meyers Blood Purifier (), which was promoted for
neuralgia, rattlesnake bites and
rheumatism. By the start of the 20th century it was the most common herbal remedy in America. Commercial cultivation began in Germany in the late 1930s, and in Switzerland in 1950, by A. Vogel. Soon chemists and pharmacologists began the task of identifying potentially active ingredients and their properties. These included ,
cichoric acid,
echinacoside, and
polysaccharides. Extracts appeared to exhibit
immunostimulant properties and were mainly promoted for the prevention and treatment of
colds,
influenza and
sepsis. Despite many different preparations and hundreds of publications, no exact identification of a truly active ingredient has been identified.
Infectious diseases
A 2014
meta-analysis found weak evidence for
Echinacea in treating, preventing, or reducing the severity of the common cold. A 2015
meta-analysis found tentative evidence that use of
Echinacea reduced the risk of repeated respiratory infections.
Side effects
When taken by mouth,
Echinacea does not usually cause
side effects, but may have undesirable interactions with various
prescribed for diseases, such as
heart disease,
bleeding, and autoimmune diseases, such as rheumatoid arthritis, lupus, or
psoriasis. Although there are no specific case reports of drug interactions with
Echinacea, safety about taking
Echinacea supplements is not well understood, with possibilities that it may cause side effects, such as
nausea, stomach upset or
diarrhea, and that it may have
with other medications. One of the most extensive and systematic studies to review the safety of
Echinacea products concluded that overall, "adverse events are rare, mild and reversible," with the most common symptoms being "
gastrointestinal and skin-related." Such side effects include
nausea,
abdominal pain,
diarrhea,
itch, and
rash.
Echinacea has also been linked to allergic reactions, including
asthma, shortness of breath, and one case of
anaphylaxis. Muscle and joint pain has been associated with
Echinacea, but it may have been caused by cold or
flu symptoms for which the
Echinacea products were administered. There are isolated case reports of rare and idiosyncratic reactions including thrombocytopenic purpura,
leucopenia,
hepatitis,
kidney failure, and atrial fibrillation, although it is not clear that these were due to
Echinacea itself. Up to 58 drugs or supplements may interact with
Echinacea.
As a matter of manufacturing safety, one investigation by an independent-consumer testing laboratory found that five of eleven selected retail Echinacea products failed quality testing. Four of the failing products contained levels of phenols below the potency level stated on the labels. One failing product was contaminated with lead.
Children under 12 years old
The European Herbal Medicinal Products Committee (HMPC) and the UK Herbal Medicines Advisory Committee (HMAC) recommended against the use of
Echinacea-containing products in children under the age of 12. Manufacturers re-labelled all oral
Echinacea products that had product licenses for children with a warning that they should not be given to children under 12 as a precautionary measure.
Pregnancy
Although research has not found increased risk of
birth defects associated with use of
Echinacea during the
first trimester, it is recommended that
pregnant women should avoid
Echinacea products until stronger safety supporting evidence becomes available.
Lactation
It is recommended that women
breastfeeding should use caution with
Echinacea products due to insufficient safety information available.
General precaution
The U.S. Food and Drug Administration recommends precaution about using dietary supplements because some products may not be risk free under certain circumstances or may interact with prescription and
over-the-counter medicines.
As with any herbal preparation, individual doses of Echinacea may vary significantly in chemical composition. Inconsistent process control in manufactured echinacea products may involve poor inter- and intra-batch homogeneity, species or plant part differences, variable extraction methods, and contamination or adulteration with other products, leading to potential for substantial product variability.
Research
Echinacea products 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 which complicate understanding of a potential effect.
Well-controlled
are limited and low in quality, with little scientific evidence that
Echinacea supplement products are useful for treating any disease.
According to Cancer Research UK, "There is no scientific evidence to show that echinacea can help treat, prevent or cure cancer in any way. Some therapists have claimed that echinacea can help relieve side effects from cancer treatments such as chemotherapy and radiotherapy, but this has not been proven either."
Although there are multiple scientific reviews and meta-analysis published on the supposed immunology effects of Echinacea, there is significant variability of products used among studies, leading to low-quality or no evidence for efficacy and safety, leading to considerable controversy. Consequently, regulatory authorities, such as the United States Food and Drug Administration, have not approved Echinacea products as safe and effective for any health or therapeutic purpose.
See also
-
List of ineffective cancer treatments
Bibliography
Books and documents
- Historical sources
-
, see also Species Plantarum
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Chapters
Articles
- Taxonomy and phylogeny
- Traditional medicine
Websites
- Databases and floras
External links
