In traditional classification systems, the highest category into which organisms are classified. The original two kingdoms, Plantae (see plant) and Animalia (see animal), were over time supplemented by others to give five kingdoms: Bacteria (or Prokaryotae; see bacteria), Protoctista (including protozoa and algae), Fungi (see fungi), Plantae, and Animalia. However, the discovery of the archaea led taxonomists to suggest a superordinate category in the taxonomic hierarchy—the domain. Modern molecular systematics supports the grouping of organisms into three domains, but the number of kingdoms is much harder to determine. Currently, eukaryotes, for example, are grouped into at least four major assemblages, or superphyla, rendering the traditional concept of kingdom obsolescent.