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A New Understanding of the Early Evolution of Flowering Plants

Text courtesy of Dr. Sean Graham:

A research team led by scientists at the UBC Botanical Garden & Centre for Plant Research announce a startling discovery in the March 15, 2007 issue of Nature concerning Hydatellaceae, an obscure family of dwarf, aquatic flowering plants. The researchers, led by garden researchers Associate Professor Sean Graham and his graduate students Jeffery Saarela (now at the Canadian Museum of Nature) and Hardeep Rai, discovered that these plants, once thought to be diminutive relatives of grasses and rushes, instead belong near the very root of the evolutionary tree of flowering plants. They have the water lilies as their closest living relatives. The flowering plants began to diversify at least 135 million years ago, in the age of the dinosaurs.

Graham and his students collaborated on this project with colleagues at the University of California, Davis, the Royal Botanical Gardens in Sydney, Australia, the University of Zurich, and Harvard University. The researcher team examined numerous genes from the two genera of Hydatellaceae, Hydatella and Trithuria. Their results are supported with a detailed consideration of Hydatellaceae plant anatomy and morphology.

The family Hydatellaceae has about ten species in two genera, Hydatella and Trithuria. The plants stand a few centimetres tall (or less) at maturity, and have multiple, minute, unisexual flowers (each lacking petals and sepals) that are collected into a compact flowering head. They grow and flower under water (up to a depth of a metre), or at the edges of drying pools. Hydatellaceae were previously thought to be monocots (a large and diverse group of the flowering plants that includes grasses, sedges, gingers, palms and onions) – largely on the basis of their narrow, pointed leaves. They are native to Australia, India and New Zealand.

The family is rather poorly known, and many details of its biology remain to be discovered. Today’s announcement overturns some previous ideas on the early evolution of flowering plants such as the water lilies Рand is the first time that a family has been ejected from the monocots.

Posted by Daniel Mosquin at 11:00 AM on March 14, 2007