First space flower

A bright orange zinnia has blossomed aboard the International Space Station, marking a first in space.

"First flower even grown in space makes its debut," US astronaut Scott Kelly wrote on Twitter, with a photo of the flower.

Growing such flowers -- zinnias are edible -- is part of a long term Nasa project known as Veggie. It is designed to produce food with an eye to long, manned missions to Mars. Such autonomy is key to astronauts' survival in space, Nasa says.

Crew on the ISS have already grown and eaten lettuce last year aboard the orbiting craft and hope to produce tomatoes by next year.

They are grown aeroponically -- without soil, in an air or mist environment. The system requires much less water and fertilizer, and plants grow three times faster than on Earth, Nasa says.