[organisms] see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Domain Bacteria Woese et al. 1990
     Phylum "Proteobacteria" Garrity et al. 2005 see Superphylum Proteobacteria Craig et al. 2010
       Class Gammaproteobacteria Garrity et al. 2005
         Order "Enterobacteriales" Garrity and Holt 2001 nom. nud.
           Family Enterobacteriaceae Rahn 1937 (Approved Lists 1980)
             Genus Providencia Ewing 1962 (Approved Lists 1980)
               1 Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980)
               2 Providencia heimbachae Müller et al. 1986
               3 Providencia rustigianii Hickman-Brenner et al. 1983
               4 Providencia stuartii (Buttiaux et al. 1954) Ewing 1962 (Approved Lists 1980)
               5 Providencia vermicola Somvanshi et al. 2006