Russia is already spearheading a multi-nation project to explore Phobos, dubbed the Phobos-Grunt mission, a sample return effort eyed for 2009.
*Revs chainsaw* Alright, lets do this!.
In all seriousness, though, those photos could be anything. The first and foremost thing to remember is that Mars is a totally different planet from Earth. With all the variety of Earth's lifeforms, we are all descended from the same basic genetic elements. In fact, there is no greater then a 10-15% difference in the genetic makeup of any animal (not sure about plants) on Earth.
On an entirely other planet, with different atmosphere, elemental makeup, radiation and gravity, odds are we wouldn't just get bigger trees. Whatever grew there might be totally different from what we even perceive as possible life.
I recall a short storey (by Arthur C. Clarke I beleive), where some Martian explorers encounter a series of small yet increasingly large pyramids that are broken at the top. What they discover is not a civilization however, but instead an animal. A creature composed of silicon and other "non-organic" elements which builds itself pyramids, grows larger, then breaks out only to repeat the process some distance on.
I'm just saying, since what where seeing here looks like big terrestrial trees, means absolutley nothing because the odds of plant life on Mars resembling Earth life that much is in fact quite low.
Then again, compared to other planets it is said Mars was quite Earth-like. And it's atmosphere is mostly carbon dioxide, which Earth plants would thrive on.
Still, my first thought seeing the pictures was that it was the crags and ravines of craters, and the photo had been colour-reversed to make it look like upward extensions of branches. I guess we'll have to see in a couple decades when we get a human down there.