You can have members of the same species of Xenia touch eachother, but Ild be a little more cautious moxing species. I think most would be OK from a direct 'fighting' point of view, but you may wind up with one variety overgrowing the other if theyre that close together. Ild also be leery to mix different general together- say Xenia next to Cespitularia. I dont know that it would hurt anything, but it sure aint gonna help...