Plant's can be altruistic to their own kin and in some cases there can develop close relationships between different species of plants that can be seen as mutually beneficial. So these plants will prosper more when grown together, than when grown in isolation.
Almost all plants have a symbiotic relationship with a species fungi known as micorrhiza that is a true symbiosis and perhaps the major reason for vegetative success.
Similarly, just about all plants rely upon another species, insect or animal, to aid in their sexual reproduction and have evolved elaborate systems to entice and reward their sexual partners.
Many Australian native plant species have developed in their seeds a specific trigger for germination involving certain chemicals contained in smoke from burning vegetation. This ensures survival of the species in a landscape that is prone to fire.

I could keep going with a longer list of plant evollutionary strategies that make you wonder just how they managed to arrive at such solutions. Many are elegant and some are quite complex. We are silly monkeys if we ignore plants and what is going on with them. Science has only just begun to scratch the surface.