Regarding the reason that garden plants seem to form clumps more readily than plants in nature, we should remember that evolution happens even on a small time scale. Gardeners are more likely to propagate and distribute clones that form clumps, so even if such clones are rare in the wild, they may become the dominant clones in cultivation. Of course the alternate explanation of greater fertility of the soil and lower competition in gardens might also explain the difference. Have people done transplanting experiments?
Lou