A quartz device is created with a default font (see
  the documentation for quartz), but it is also possible
  to specify a font family when drawing to the device
  (for example, see the documentation for gpar in the
  grid package).  The font family sent to the device is a simple string name, which must be
  mapped to something more specific to quartz fonts.  A list of
  mappings is maintained and can be modified by the user.
  The quartzFonts function can be used to list existing
  mappings and to define new mappings.  The quartzFont
  function can be used to create a new mapping.
  Default mappings are provided for three device-independent font family
  names: "sans" for a sans-serif font, "serif" for a serif
  font and "mono" for a monospaced font.