ungraded, unordered, unranked

from The Collaborative International Dictionary of English v.0.48

nonhierarchic \nonhierarchic\ nonhierarchical
\nonhierarchical\adj.
   Not arranged in a hierarchy. Opposite of {hierarchical}.
   [Narrower terms: {ungraded, unordered, unranked}]
   [WordNet 1.5]