Plant species of the week: could sweet gums (Liquidambar styraciflua) help fight swine flu?

April 27, 7:57 PMPhiladelphia Home Gardening ExaminerMelissa Miles

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Sweet gum leaves and fruit

With the recent swine flu outbreak (and the resulting bump in sales of the anti-viral drugs thought to combat the virus), I am featuring the sweet gum as the plant of the week -  this North American native has shown promise as a potential source of the active ingredient in some anti-viral medications.

The sweet gum is a large (25' - 30' m mature height), deciduous tree that grows through out the warm, temperate areas of the U.S., (including the mid-Atlantic region). Sweet gums are, perhaps, best known for their star shaped leaves and distinctively spiny fruit. Researchers have found that seeds of the sweet gum contain significant amounts of shikimic acid, a compound used in the production of the prescription anti-viral drug oseltamivir (Tamiflu® is the well known brand-name of the drug produced by Roche Pharmaceuticals). Oseltamivir works by blocking the replication of influenza virus, but the primary source of shikimic acid used to produce oseltamivir is the seed pod of the Chinese star-anise (Illicium verum), a plant native to Asia (the pods are most often used as a spice in Asian cuisine).

Shikimic acid 

During the bird flu virus outbreak a few years ago, oseltamivir was in short supply, primarily because of the low yield of shikimic acid obtained from the star anise plant. Though sweet gum seeds have a smaller percentage of the active compound than that found in Chinese star-anise pods (sweet gum fruit yields about 1.5% shikimic acid, star-anise about 3 - 7%), sweet gum fruit is relatively abundant in North America. In order to extract the shikimic acid from sweet gum seeds, the fruits need to be harvested when still green. Each fruit contains many small seeds, each tree in turn, produces hundreds or thousands of seeds; but sweet gum trees do not start producing the fruit until they are ten (or more) years old. Smaller amounts of shikimic acid have also been isolated from the bark and leaves of the sweet gum tree, but sweet gum seeds are thought to hold the most promise as a source of shikimic acid for anti-viral drug production.

sweet gum tree

Sweet gums are often planted as ornamentals because they display a vibrant fall leaf color, are fast growing and are considered fairly drought tolerant.  The trees prefer full sun, do well in various soil conditions, and make nice shade trees when planted in a landscape as the mature tree can boast a canopy spread of > 40'.  Because the spiny fruits can be a nuisance (although they are great for arts and crafts projects), many home gardeners prefer to plant the (not quite as cold tolerant) fruitless cultivar: 'Rotundiloba'.  

 If you are interested in viewing my previous Plant of the Week installments, please visit: 

Plant species of the week: Nasturtium, an edible flower

Plant species of the week:  paw paw