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The ideal plant for producing cellulosic ethanol, he added, is Miscanthus, a perennial grass native to subtropical and tropical regions of Africa and southern Asia, which is used as an ornamental plant in the United States.

What makes Miscanthus so special?

''It uses less water per gram of biomass produced than other plants,'' he said. ''For example, to make a pound of alfalfa or spinach requires about 600 pounds of water, while to grow a pound of Miscanthus requires only about 200 pounds of water.''

According to Somerville, Miscanthus produces about twice as much biomass per acre without irrigation than other grasses, and reaching the president's target of 35 billion gallons of biofuels annually would require putting far fewer acres of land into Miscanthus production.

The main reason behind the call for increased biofuel production is to reduce emissions of greenhouse gases, not because we are running out of fossil fuels, he added. ''There are reserves of coal for 200 years at least, and coal can be liquefied into fuel, but it produces an awful lot of CO2,'' he explained.

Biofuels, on the other hand, are carbon-neutral sources of energy, Somerville said, noting that plants absorb atmospheric carbon dioxide during photosynthesis, which compensates for the CO2 that is released when biofuels burn.

Environmental costs

Some environmentalists criticize the use of biofuels by arguing that planting large quantities of corn or grass to produce ethanol will require widespread deforestation, which threatens biodiversity. ''It depends on what acres of land one uses [to plant Miscanthus],'' said Somerville, who advocates growing biofuel crops on land currently used for food production.

''There's a lot of deforestation certainly going to take place in tropical regions, because those countries are going to develop biofuel busines
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