Maximum parsimony analysis of nuclear SSU rDNA sequences was utilized to infer the phylogenetic relationships of representatives of the macrolichen families Cladoniaceae, Sphaerophoraceae, and Stereocaulaceae (Lecanorales subord. Cladoniineae, Ascomycotina). Farris’ parsimony jackknifing, and a similar jackknife strategy with branch-swapping and multiple addition sequences in PAUP*, were performed to assess branch support. The results indicate that the Sphaerophoraceae should be emended to include Neophyllis (formerly Cladoniaceae or Stereocaulaceae) and Austropeltum (formerly Stereocaulaceae), and it is suggested that the type of boundary tissue present is a synapomorphy for the family. The families Sphaerophoraceae and Bacidiaceae form a clade, together with Psora decipiens, Tephromela atra and Scoliciosporum umbrinum. The Cladoniaceae should be emended to include Pilophorus, and the genera Metus, Cladia and Heterodea should also be included in the family. The sometimes-recognized families Cladiaceae and Heterodeaceae are shown to be derived from within Cladoniaceae. The Stereocaulaceae is recircumscribed to accommodate Stereocaulon only. Neither the possession of podetia/ pseudopodetia, a dimorphic, cladoniiform thallus, nor the presence of cephalodia, is a morphological synapomorphy for a monophyletic group in our analysis. Optimising ascus structures onto one of the most parsimonious trees suggest that tube-like apical structures may well be primitive characteristics within the Lecanorales. The two lecanoralean suborders Lecanorineae and Cladonineae are both paraphyletic groups in the present analysis. It is pointed out that if further studies confirm that Stereocaulon is the sister-group to the Cladoniaceae, as circumscribed here, then there may be no reason to accept the two families Cladoniaceae and Stereocaulaceae as distinct. Branch-swapping and several random-addition sequencesimprove resolution, adding several supported groups in the topology, and improve support values for groups already supported by parsimony jackkniring analyses, and we suggest a procedure for implementing this by using PAUP*