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In November of 2011, the
International Union for the Conservation of Nature (IUCN) updated its Red List
of Threatened Species, documenting an increasing threat faced by several
plants, including some important medicinal species.1 IUCN describes
its Red List as “the world’s most comprehensive information source on the
global conservation status of plant and animal species.”2 Though
IUCN often partners with the Convention on International Trade in Endangered
Species of Wild Fauna and Flora (CITES), the Red List is separate from the
CITES appendices, which document the conservation status and risk assessments
of animals and plants while also serving as an international agreement implementing
trade restrictions followed by CITES members.3
For the Red List, IUCN and partner organizations, such as the Royal Botanic
Garden, Kew (in the United Kingdom), assess thousands of plant and animal
species, considering which of 8 extinction risk levels a species should be
classified as if no conservation action were to take place.2 The 8
risk levels are classed as follows: data deficient, least concern, near
threatened, vulnerable, endangered, critically endangered, extinct in the wild,
and extinct. Factors considered in the classification process include
population trend, population size and structure, and geographic range.
According to Danna Leaman, PhD—the chair of IUCN’s Medicinal Plants Specialist
Group (MPSG)—many medicinal species are included on the Red List, but it has
been difficult to determine exactly which ones and how many (e-mail, December
12, 2011). In order to address this issue and document the conservation status
of medicinals, the MPSG began building a Global Checklist of Medicinal Plants
based on international, regional, and national pharmacopeias and medicinal
floras, as well as the NAPRAlert database at the University of Illinois at
Chicago, developed by the late Professor Norman Farnsworth. In May of 2010, the
group teamed with TRAFFIC International to compare the list that then consisted
of 16,600 species (and now includes ca. 27,000) with the online and off-line
versions of the IUCN Red List.
They found that just 3% of the world’s well-documented medicinal flora had been
evaluated for global conservation status. Now the team is comparing its Global
Checklist of Medicinal Plants with the updated 2011 Red List. Dr. Leaman said
they hope to have the comparison completed sometime in 2012. “It will not be
possible to use these data to monitor the trend in conservation status of
medicinal plants unless and until there is a global assessment effort focused
on medicinal plants,” said Dr. Leaman, noting that such a proposal has been
created and is in need of funding.
Decline of Important Yew Tree Species
The updated Red List documents an increasing threat faced by the valuable
medicinal plant Taxus contorta, a
species of yew tree growing in Afghanistan, Pakistan, western Nepal, and
northwestern India. T. contorta—the
bark of which contains the anticancer compound paclitaxel (brand name Taxol®)—was
listed as endangered, an increase from its previous classification as
threatened. IUCN wrote that T. contorta’s
classification was changed “due to over-exploitation for medicinal use and
over-collection for fuel wood and fodder.”1
In 1971, Mansukh Wani, PhD, and Monroe Wall, PhD, isolated the secondary
metabolite Taxol from the bark of the
Pacific yew tree (T. brevifolia), a
small tree native to the Pacific Northwest of the United States.4,5
The bark, leaves, fruit, and twigs were previously screened for anticancer
properties by the US National Cancer Institute and Department of Agriculture.
In 1992, the US Food and Drug Administration (FDA) approved Taxol for use in
patients with ovarian cancer. The drug was very successful, as the American
Botanical Council reported in 1997 that there were “numerous cases of partial
or complete remission.”4 FDA later approved Taxol for use in
treating breast, lung, and prostate cancers. Scientists are also studying 17
Taxol analogs in clinical trails for 7 other types of cancer, and according to
the Research Triangle Institute—where Drs. Wani and Wall worked at the time of
their Taxol work—recent studies suggest that Taxol may help treat Alzheimer’s
disease and scleroderma.5
The knowledge of Taxol’s medicinal potential led to drastic decreases in wild
Pacific yew tree populations due to widespread felling of trees, as well as the
harvesting of bark, a practice that severely harms the tree.4
Researchers began looking for Taxol in other yew tree species, and it is now
known that all 11 species—including T.
contorta—contain either Taxol or intermediate compounds that can be converted
to Taxol. While some of these species, such as European yew (T. baccata), yield these compounds in
renewable needles or fungus, the tree bark is still often harvested, as is the
case for many T. contorta populations.
Though covering a relatively large distribution area, T. contorta populations are small and genetically isolated, mostly
confined to declining coniferous forest habitats.6 Fifty percent of
habitats in Afghanistan and 90% in northwest India and western Nepal have been
destroyed. An estimated 80% of habitats in Pakistan are also declining from
overexploitation.
According to current science, using synthetic Taxol to replace the dependence
on yew tree populations is not a realistic alternative. The difficult process
of creating the synthetic version has produced only 30 milligrams of supplies.7
Despite the recent announcement by a team of scientists at the Scripps Research
Institute that sizable quantities of synthetic Taxol could be achieved by producing
a relative of Taxol in order to eventually synthesize Taxol, the researchers
say this could take years. According to Scripps, “The current commercial Taxol
production method, which involves culturing cells from the yew tree, is more
economical than any new synthesis is likely to be.”
According to an interview with IUCN’s Red List Unit Manager, Craig
Hilton-Taylor, with the UK newspaper The
Guardian, “It is possible to extract Taxol from clippings, so harvesting,
if properly controlled, can be less detrimental to the plants. Harvest and
trade should be carefully controlled to ensure it is sustainable, but plants
should also be grown in cultivation to reduce the impact of harvesting on wild
populations.”8
Additional Medicinal Plants Documented
on Red List
The conservation statuses of several other medicinal and useful plants were
assessed on the updated Red List. The coco de mer (Lodoicea maldivica)—the world’s largest and heaviest plant seed9—was
moved from vulnerable to endangered status.1 Also called the double
coconut palm, sea coconut, and Seychelles nut, this palm tree produces kernels
or seeds that have been used traditionally among locals for aphrodisiac purposes.1,9
The endosperm of the seeds are also used in Chinese medicine to treat cough, most
often in the form of soups.10 Despite being protected by the
Breadfruit and Other Trees Act of Seychelles, IUCN notes the coco de mer’s
biggest threats are fires, harvesting, and poaching.1,11
Though growing extensively across Europe, snowdrop (Galanthus nivalis) was listed as near threatened due to
over-harvesting in certain areas for horticultural and medicinal purposes.12
Long used by villagers as traditional medicine, snowdrop is considered
moderately toxic but also contains galantamine, a drug approved by the US Food
and Drug Administration for the treatment of Alzheimer’s Disease.13,14
The water onion (Crinum thaianum)—an
aquatic member of the lily family used as a skin cream in Thailand—was listed
as endangered,12 and the Chinese Water Fir (Glyptostrobus pensilis)—a conifer whose aromatic wood is used for
many purposes including musical instruments15—was moved from
endangered to critically endangered.12
—Lindsay Stafford
References
1. Another leap towards the Barometer of Life [press release]. Gland,
Switzerland: International Union for the Conservation of Nature. November 10,
2011. Available at:
www.iucn.org/about/work/programmes/species/red_list/?8548/Another-leap-towards-the-Barometer-of-Life.
Accessed November 11, 2011.
2. What is CITES? Convention on International Trade in Endangered Species of
Wild Fauna and Flora website. Available at: www.cites.org/eng/disc/what.php.
Accessed December 30, 2011.
3. About the IUCN Red List. International Union for the Conservation of Nature
website. Available at: www.iucn.org/about/work/programmes/species/red_list/about_the_red_list/.
Accessed December 28, 2011.
4. Camptothecin and Taxol: natural anti-cancer agents. HerbalGram. 1997; 40:21. Available at:
http://cms.herbalgram.org/herbalgram/issue40/article181.html.
5. Noted cancer researcher Mansukh Wani closes the books on 44-year career
[press release]. Research Triangle Park, North Carolina: Research Triangle
Institute International. January 9, 2007. Available at:
www.rti.org/news.cfm?nav=6&objectid=026FAA96-2D85-4212-912BE7E3887433E7.
Accessed December 27, 2011.
6. Taxus contorta. The IUCN Red List of Threatened Species website. Available
at: www.iucnredlist.org/apps/redlist/details/39147/0. Accessed December 27,
2011.
7. Scripps research team achieves critical step for opening elusive class of
compounds to drug discovery [press release]. La Jolla, California: Scripps
Research Institute. November 6, 2011. Available at:
www.scripps.edu/news/press_releases/20111106baran.html. Accessed December 27,
2011.
8. Gersmann H and Aldred J. Medicinal tree used in chemotherapy drug faces
extinction. The Guardian. November 9,
2011. Available at:
www.guardian.co.uk/environment/2011/nov/10/iucn-red-list-tree-chemotherapy.
Accessed December 27, 2011.
9. Rilwan A. The mystery of Maldive Coconut (Lodoicea maldivica). Bluepeace. May 2004. Available at: www.bluepeacemaldives.org/news2004/coconutmaldivica.htm.
Accessed November 11, 2011.
10. Mak C, Mok C. Molecular identification of Lodoicea maldivica (coco de mer) seeds. Chinese Medicine. 2011;6(34).
11. Lodoicea maldivica. The IUCN Red List of Threatened Species website.
Available at: www.iucnredlist.org/apps/redlist/details/38602/0. Accessed
November 11, 2011.
12. 2011 photo gallery. The IUCN Red List of Threatened Species website.
Available at: www.iucnredlist.org/photos/2011. Accessed November 11, 2011.
13. Galantamine. MedlinePlus Drug Information. US National Institutes of Health
website. Available at: www.nlm.nih.gov/medlineplus/druginfo/meds/a699058.html.
Accessed December 28, 2011.
14. Heinrich M, Lee Teoh H. Galanthamine from snowdrop—the development of a
modern drug against Alzheimer's disease from local Caucasian knowledge. J Ethnopharmacol. 2004;92(2-3):147-62.
15. Glyptostrobus pensilis. The Gymnosperm Database website. Available at:
www.conifers.org/cu/Glyptostrobus.php. Accessed November 11, 2011.
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