Micro-morphological studies on mosses are not common, but have the potential to illuminate the nature of taxonomic characters. Data on the structure and development of leaf cell papillae in the Sematophyllaceae obtained using light and scanning electron microscopy techniques are presented to assess developmental similarity and congruence with taxonomy. Two morphological and developmentally distinct kinds of papillae were identified; 1) dome-shaped to conical, tapering to a firmly rounded apex (“conical”), and 2) a more flaccid, baggy form, that is often flat-topped and wider distally than proximally (“baggy”). Conical papillae first appear as slight protrusions that gradually increase in height, whereas baggy papillae progress through a series of developmental sizes and forms. Conical papillae occur in most papillose taxa, whereas baggy papillae are present only in Taxithelium subgenus Taxithelium.