We've written before about Prius plug-in conversions, but here's a new wrinkle: a 2008 Toyota Prius plug-in that's also running on biofuel derived partly from algae grown specifically as a source of fuel.

It's the "Algaeus," a project of the Veggie Van Organization in Santa Monica, California. The fuel comes from Sapphire Energy in San Diego, which says it mixes "hydrocarbons refined directly from algae-based Green Crude, extracted through [our] proprietary process, and fossil fuels."

The Algaeus is just starting a 30-day tour across the country from San Francisco to Manhattan.

Its promoters toss around the figure of "150 miles per gallon," though like all such figures (like GM's 230-mpg claim for its 2011 Chevy Volt), it requires specific assumptions to make the math work.

The MPG figure is actually miles per gallon of gasoline extracted from crude oil, for example. It doesn't included the algae-fuel component, or the fuel burned to generate the plug-in electricity.

Future Algaeus stops include Cheyenne, WY (Sept. 11th), Lincoln, NE (Sept. 12th), Chicago, IL (Sept. 13th), Detroit, MI (Sept. 14th), Cleveland, OH (Sept. 15th), Erie, PA (Sept. 16th), Washington DC (Sept. 17th), and New York City (Sept. 18th).

[press release from Sapphire Energy and Veggie Van via Toyotapedia]