Hydatellaceae, a family of tiny water plants previously thought to be grasses, turns out to be an ancient flower lineage, closely related to water lilies (Nymphaeales). Its kinship with the lily puts it near the base of the flowering plant evolutionary tree, raising new questions about how flowers evolved.
Sean Graham, a professor at the University of British Columbia, and his colleagues, discovered Hydatellaceae’s true identity after they tried to place the plant family in with the monocots—along with palms and grasses, but it’s DNA didn’t fit. “Lo and behold, it came out not with grasses and not even with the monocots but actually very close to the origin of the modern flowering plants, right beside the water lilies,” says Graham. “It was a shocker.” The results were published in the journal Nature this week.
Graham’s lab analyzes plant DNA to find the plant's closest relatives and where it sits on the evolutionary tree. “We can look at the DNA sequences of organisms and get a fix on how similar or different they are to each other…And that gives us a real window into the past,” says Graham.
LISTENING STATION: SOUND BITES
SEAN GRAHAM
UBC BOTANICAL GARDEN AND CENTRE FOR PLANT RESEARCH
DEPT OF BOTANY
UNIVERSITY OF BRITISH COLUMBIA
James Doyle a professor at University California Davis and co-author on the study, looked at the anatomy of the Hydatellaceae for more clues. Although Hydatellaceae’s tiny petal-less flowers and sharp miniature leaves are nearly opposites to its sister’s floppy blossoms and giant rounded leaves —some of the less obvious anatomical features of water lilies and Hydatellaceae are strikingly similar, Graham says.
For instance, the seed coat of Hydatellaceae closely matches that of water lilies. Plus, water lilies have an unusual seed storage tissue. Hydatellaceae has the same kind. Graham says: “We looked quite carefully at the anatomy and as soon as we did that we saw that everything began to fit into place.”
Graham says Hydatellaceae's placement on the flower family tree may make us rethink flower evolution. In Hydatellaceae, dozens of flowers are squeezed into one flower head, for example. “One possibility is that this plant might be on the borderline between what we think of as a flower and an inflorescence, which is a collection of flowers.” Have we uncovered a missing link with Hydatellaceae? No, Graham says: “It’s not a missing link, it’s a link that we had that we didn’t know.”
-Flora Lichtman
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