'Desert Rhubarb' Harvests Water

July 8, 2009 -- In the mountains of Israel's Negev Desert, a rare plant breaks the rules of desert living. Rather than keeping its leaves tiny to conserve water, desert rhubarb unfurls large sheets of leaves up to 25 inches across.

New research explains the plant's unconventional size. Its waxy leaf surfaces are covered with enormous ridges and valleys that evoke the mountains on which it grows. The steep slope of the leaf surfaces funnels 16 times more water to the plant's base than it could gather without its "irrigation system," the researchers found.

Study of this unique plant began when Simcha Lev-Yadun, Gadi Katzir and Gidi Ne'eman of the University of Haifa-Oranim ventured into the Negev Desert to prepare to teach a class on the desert. They came upon a desert rhubarb plant, which grows only in the mountains of Israel and Jordan. "We discussed it, and it became clear that the function of those unbelievable leaves is to collect water. They act like mountain ridges to collect water into the valleys," Lev-Yadun said.

The team tested their hypothesis by sprinkling water on the plants, and by observing the plants during a rainstorm. They measured the depth of water infiltration both near the plant and at a distance.

"When the annual rainfall is three inches, they see something like 17 inches of rainfall," Lev-Yadun said. Compared to the one inch of rain captured by other nearby desert plants, desert rhubarb captures between 16 and 17 times more water. This "leaf-made mini oasis", as the authors describe it, creates a Mediterranean climate for the plant in the middle of the desert.

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Many desert plants have both a deep root, which can gather water from deep soil, and a system of shallow roots designed quickly to mop up any rainfall at the surface. Desert rhubarb lacks this shallow root network, since the leaves collect water before it wets the soil and funnel it directly to the deep root.

The team published their results in Naturwissenschaften.

"It's a fascinating discovery. I'm not aware that anybody else has demonstrated water-harvesting abilities," Mark Dimmitt, Director of Natural History at the Arizona-Sonora Desert Museum in Tucson told Discovery News.

But other desert plants probably do it, too, he added. "There are a number of species of agaves whose leaves are arched upwards and they are channeled, so logically it appears that water would be channeled to the base of a plant."

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