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Winter 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

January 31, 2012

Sweetgum fruits

An abundant remedy for the flu? Never mind.

By late January, when most trees have been stripped of their holiday decorations, sweetgum trees are still hanging on to many of their own spiky ornaments. The tree's russet, prickly fruits, or "gumballs," resemble a cluster of twisted, gaping bird beaks — or a three-dimensional version of the biohazard symbol. They are so distinctive and durable that some people gather them in December to craft into holiday decorations.

In late autumn, before the gumballs surrender to glue guns and glitter, they complete their natural duties by opening their beaks and releasing a few winged seeds Those aborted seeds raised eyebrows in 2008, when chemist Thomas Poon and his team of student researchers revealed that sweetgum's aborted seeds are rich in shikimic acid, a hard-to-find compound used to synthesize Tamiflu, a drug that helps curtail and prevent influenza infections. Before the discovery, the primary source for shikimic acid was star anise, where it is found in limited concentrations.

Nevertheless, sweetgum missed its opportunity to become a modern pharmaceutical plant. "A much better process for producing shikimic acid was developed shortly after our discovery," says Poon. "The new process uses genetically modified bacteria, which can be efficiently grown in labs to produce the shikimic acid."

Bacteria, however, make for a lousy wreath.

SOURCES: Claremont McKenna, Pitzer and Scripps colleges; Tetrahedron Letters; U.S. Forest Service

Sweetgum fruits, Liquidambar styraciflua