Half of the world's yet-to-be-discovered flowering plant species may already have been collected, and now languish in herbarium cabinets.

While reclassifying varieties of Strobilanthes, a genus of purple-flowered plants from Asia, Robert Scotland of the University of Oxford, UK, and his colleagues noticed that many of the 60 species they described had been collected many years before. This lag ranged from 1 to 210 years and averaged more than 30 years for more than 3,000 species in 6 plant genera, including Strobilanthes. Just 16% of these plants were classified within 5 years of discovery.

If this trend holds for other flowering plants, 47% to 66% of the planet's estimated 70,000 undiscovered species are waiting to be unveiled in herbaria.

Proc. Natl. Acad. Sci. USA doi:10.1073/pnas.1011841108 (2010)