After four years of debate, an international team of scientists from 25 institutions has agreed to a good—but not great—standard plant DNA bar code.

This metaphorical bar code—a short sequence of DNA unique to every species—could pave the way for a handheld plant “scanner” that could be used to quickly identify species intercepted from illegal logging operations or to identify potentially toxic plants in an emergency situation. It will also make the day-to-day work of identifying and studying new species a whole lot easier.

Scientists who study animals have long used the mitochondrial gene CO1 to build a DNA library of 60,000 species.  But getting botanists to agree on a single standard has been challenging because of the genetic diversity of plants.  Many research groups moved ahead with large-scale projects using their preferred gene or gene combination before a consensus had been reached. 

“It’s a very contentious issue,” Kenneth Cameron of the University of Wisconsin–Madison told Nature in 2008, “There are a lot of politics and personalities involved.”

But this week in Proceedings of the National Academy of Sciences, Cameron and the rest of the Consortium for the Barcode of Life Plant Working Group, recommended using two genes, rbcL and matK as the most “pragmatic” option.  The gene matK alone had previously been shown to classify 90 percent of plant species in one study, but it doesn’t work well in every plant group, so the scientists tacked on the second gene which is more of a jack-of-all-trades.

In a test run, the scientists say the standard bar code can only discriminate 72 percent of species across the plant world, with the remainder being properly assigned to closely related species groups. 

“There is little doubt that the approaches used in plant DNA bar coding will be refined in the future,” the authors write, but “the key foundation step for plant bar coding is in reaching agreement on a standard set of [genes] to enable large-scale sequencing and the development of a global plant bar coding infrastructure.”

Image of barcode courtesy Carsten Brix via Flickr