Which genus, Callianthemum or Chamaemelum, is native to more continents?
Callianthemum: Callianthemum is a genus that consists of 24 species of little rhizomatous herbs from high mountains in Europe, Central Asia and East Asia. Chamaemelum:  They are native to Europe but most species can be found scattered in other continents where they have been introduced.
Callianthemum