Saw it tonight. It was good... Anyhow, about the vegitation, here was my thinking, which sorta fits in with the link
"Apparently, the vegetable kingdom on Mars instead of having green for a dominant color is of a vivid blood red tint," Wells wrote. "At any rate, the seeds which Martians (intentionally or accidentally [sic]) brought with them gave rise in all cases to red colored growths. Only that - known popularly-as red weed, however, gained any footing in the competition with terrestrial forms."
...The red weed like the aliens, however, seems determined to put roots down on earth in the effort to transform the conditions here to suit the aliens.
Basically, I was thinking, when I saw this that the vegitation was there as some form of teraforming. Thing about what would happen if we were to go to Mars for instance. We need oxygen, the atmosphere of that planet doesn't have it in abundence. (Heck Mars doesn't have much of an atmosphere, period.) What's the first thing we'd have to do to collonize it? Teraform it's surface, and make the atmosphere suitable for us to breath.
It's not inconceivable we might try to transpose Earth based plants there, to help with oxygen production, assuming the other stuff (aka water) is available to help water them, and help them grow...
As such, I was thinking much the same, alien vegitation that could help with the teraforming of the planet to what they would need to survive...