Plants are generally very competitive. They compete for food, light, carbon dioxide, water. Some plants are very good at competition - look how widespread grass is. I have a theory that, much like some parasites that can affect their host's behaviour*, grass can affect human behaviour. Why else would some people be so driven to spend hours making conditions just right for the perfect sward? "Can't be having any of those nasty weeds spoiling the picture-perfect lawn", thinks the lawn obsessive. "Ha ha!", thinks the lawn (which I imagine to have a hive mind), "my competitiors have been removed - more space for me!"
Some plants, however, drop out of the rat race. Not for them the constant fighting for space, food and water. They take a step sideways and look for somewhere to live that provides them with a bit of a challenge, but which other plants find much harder to cope with. Like a plant I met for the first time yesterday. We went for a walk in North Wales, in an area which has a rich lead mining history.
Lead isn't very good for most organisms. But some plants can cope with it and thrive on the competition-free waste heaps in these sites. There's quite a lot of research going on about how the use of these plants could help to remove toxic materials from contaminated sites - phytoremediation. Or, you could just do what we did yesterday - admire the rich carpet of Spring Sandwort (AKA leadwort) getting along just fine in an area where few other plants were growing.
* Quick overview of some examples of this phenomenon here, but there are many more examples.