There have been 2 space missions to mars thet softlanded a robot vehicle The first one got damaged during the landing so I could not move, but it did sit there observing in all direction. It found neither animals nor plants. The second one was luckier, it got down undamaged and drove around for several days but again found no trace of animals or plants.
So if there are any plants they must either grow undergound or all in some small area that the rower missed (that is entirely possible. to get water plants would need to grow near the poles where there is condensation during Martian winter)