(Reuters) - Eucalyptus leaves are the main food supply for Australia's koalas, but there is a lot more to the tree than that.

It is native to Australia but has become the world's most widely planted hardwood tree. The eucalyptus tree is a source of timber, fuel, cellulose and medicinal and industrial oils, and scientists are looking to maximize its potential in biofuels.

An international team of researchers this week unveiled the genetic blueprint of the tree species Eucalyptus grandis and identified among its 36,000-plus genes the ones involved in critical biological processes controlling tree growth and wood formation, flowering and other qualities.

"The main interest is understanding how these trees grow so fast and how they are able to produce such large amounts of cellulose," scientist Zander Myburg of the University of Pretoria's Forestry and Agricultural Biotechnology Institute said in a telephone interview on Thursday.

"There's an interest in cellulose in the context of breaking the cellulose down into sugars, which can be fermented into biofuels. But really these trees are widely used industrially for cellulose-related products and timber, pulp and paper production."

Also called gum trees, eucalyptus trees have grown for tens of millions of years across the Australian landscape, and are closely identified with that continent. The koala, one of Australia's characteristic marsupials, munches its leaves. Its wood also is used in making the Australian aboriginal wind instruments called didgeridoos.

Eucalyptus trees, with their speedy growth rate and exceptional wood and fiber properties, are now grown in about 100 countries on six continents.

Some scientists see great potential in these trees as a biomass energy crop. The study identified genes controlling the final steps for the production of cellulose and "hemi-cellulose", both carbohydrates that can be used for biofuel production.

"We have a keen interest in how wood is formed," added Gerald Tuskan of the Oak Ridge National Laboratory and U.S. Department of Energy Joint Genome Institute, another of the lead researchers.

"A major determinant of industrial processing efficiency lies in the composition and cross-linking of biopolymers in the thick secondary cell walls of woody fibers. Our analysis provides a much more comprehensive understanding of the genetic control of carbon allocation towards cell wall biopolymers in woody plants - a crucial step toward the development of future biomass crops," Tuskan said in a statement.

The study was published in the journal Nature.

(Reporting by Will Dunham; Editing by James Dalgleish)