Toyota is looking to a greener future — literally — with dreams of an ultralight, superefficient plug-in hybrid with a bioplastic body made of seaweed that could be in showrooms within 15 years.

The kelp car would build upon the already hypergreen 1/X plug-in hybrid concept, which weighs 926 pounds, by replacing its carbon-fiber body with plastic derived from seaweed. As wild as it might sound, bioplastics are becoming increasingly common and Toyota thinks it’s only a matter of time before automakers use them to build cars.

“We used lightweight carbon-fiber reinforced plastic throughout the body and frame for its superior collision safety,” project manager Tetsuya Kaida said of the 1/X, which is pronounced “one-xth.” “But that material is made from oil. In the future, I’m sure we will have access to new and better materials, such as those made from plants, something natural, maybe something like paper. In fact, I want to create such a vehicle from seaweed because Japan is surrounded by the sea.”

A kelp car is not as far-fetched as it might sound. Bioplastics are being used for everything from gift cards to cellphone cases. Demand for the stuff is expected to hit 50 billion pounds annually within five years, a figure that would account for 10 percent of the world market for plastic, according to USA Today. A company called NatureWorks claims the production of its bioplastic Inego produces 60 percent less carbon dioxide than petroleum-based plastic and requires 30 percent less energy. And Oakridge National Laboratory has explored the possibility of producing carbon fiber from wood pulp.

Toyota is laying out its green vision of the future ahead of the Melbourne Motor Show, where it will highlight three sweet hybrids — the next-gen Prius, a cool Camry concept designed in Australia and the 1/X, so named because its carbon footprint is a fraction of that of other cars.

“The 1/X concept is a vehicle that completely redefines what it means to be environmentally considerate,” David Buttner, senior executive director of sales and marketing, said in a statement. “The name says it all: a car that weighs a fraction of the others in its class today and uses a fraction of the fuel.”

The 1/X has been kicking around the show circuit for more than a year, and the photo is from its North American debut at the 2008 Chicago auto show. It features a tiny 500cc engine and weighs about one-third as much as the Prius while offering about as much interior space. It’s got a flex-fuel engine and electric motor powered by lithium-ion batteries.

But don’t expect to drive a Toyota Sea-Class anytime soon.