These have pods that are filled with oxygen making them explosive if hit.
They are seeded onto a planet in order to produce an atmosphere.
1000mu's of vines per sector will produce an atmosphere in 1 year.
After a year, they can also be tapped for a resource of vine seeds. The sector used for the seeding will produce 1mu/week seeds per 100mu's seeded.
Note that the sector used to seed the vines will be clearly visible by a low pass scan.