Abstract.A cladistic analysis of thirty‐five morphological characters is used to produce a cladogram for the twenty‐four American species ofSialisfound north of Mexico, two European species, and three species ofProtosialis. Three species groups (americana, califomicaandinfumata) proposed by Ross 1937 are shown to be monophyletic.Sialis, Protosialis, and theaequalisspecies group as currently constituted, are paraphyletic;S.nevadensisis nested withinProtosialisandProtosialisis nested withinSialis. Character evolution is evaluated in the light of a phylogenetic hypothesis, and structural modifications are found to correlate with presumed functional constrai