A schematic phylogenetic tree of organisms that have contributed spacer sequences to archaea. The direction of arrows points from the spacer towards its match. Red arrows, within genus matches; purple arrow, between genera matches; black arrows- matches between families, classes or domains; blue arrows, the match is to a virus known to infect that species (not including provirus sequences within genomes of cellular organisms). Boxes denote number of spacer hits between two organisms, absence of a box denoting a single match. "@", "#" equal best hits. Within species matches are not shown.