I'm sure they can run into each other, but I'm assuming survival of the fittest will kick in and one of them will have won, while the other runs with its tail between its legs.

LET THE BATTLE BEGIN!!!!!!!!!

Simple answer - makes sense! Thanks!

Actually I have seen a collection where they ran together and stayed mixed together, producing an unpleasant (confused) effect. Better to plant them far apart from each other.

I've seen a beautiful grove of yellow and black runners mixed together. It looked like they were originally planted next to eachother, then they grew mixed in the center. Very nice, i bet if you used two of the same species but different varieties , it would look great.

The key is growing varieties that attain the same height. I hear Nigra with P. Aureosulcata aureocalis is a nice combo.

I'm growing Phyllostachys nigra and P. bambusoides castellon mixed together in a single grove, giving me a combination of green, yellow/green, and black culms. The only extra maintainance required is the need to prune out shoots more heavily on the nigra to keep it from gaining the upper hand.