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Taxonomy is often seen as a dusty, old-fashioned science, but the molecular insights gained from examining species' DNA have invigorated the newer field of phylogenetics — and helped scientists classify organisms by reconstructing their evolutionary relationships. On page 312, Sean Graham, a plant molecular systematist at the University of British Columbia in Canada, and his colleagues show how the Hydatellaceae, a group of aquatic plants that has defied traditional classification, can provide clues to the evolution of flowering plants.

How are classical taxonomic relationships being changed by molecular findings?

We are overturning taxonomic concepts that go back centuries. In 1999, we found that Amborella trichopoda, a shrub found in New Caledonia, defines the phylogenetic 'root' of the flowering plants. Amborella may be the sister group of all other flowering plants. This discovery rocked the botanical world. Molecular data have also confirmed that dividing flowering plants into dicots and monocots, based on having two versus one seed leaves, is obsolete. The dicots have been broken up, and textbooks rewritten.

Why did you pick the Hydatellaceae?

These small plants were lumped with grasses as monocots, based on superficial structural similarities. Some preliminary molecular evidence also seemed to place them near the grasses. But other features didn't add up. When we finally got our first samples from Australia, genetic evidence showed that the family fits near the very base of the flowering-plant phylogenetic tree, with the water-lilies. Every gene my graduate students investigated gave us the same oddball result, as did examination of structural features.

What does this mean for plant phylogeny?

It causes us to question what we thought we knew. There is some debate about whether the first angiosperms were aquatic or terrestrial. Our work doesn't answer that question. We just show that the water-lily lineage is more diverse than we had thought, and in unexpected ways. It could also help us understand where certain fossil angiosperms belong.

Is linnaean classification still useful?

This is quite a controversial subject. The traditional rank-based classification schemes have had a big overhaul in the past decade. The bigger question, under active debate and fuelling hot tempers, is whether we need to have a rank-based taxonomy at all. But the linnaean system has worked for hundreds of years, so to break with that is a real struggle for many biologists.