  Whereas penumbral models during the last 15 years have been successful in
explaining Evershed flows and magnetic field inclination variations in terms of
flux tubes, the lack of contact between these models and a convective process
needed to explain the penumbral radiative heat flux has been disturbing. We
report on recent observational and theoretical evidence that challenge flux
tube interpretations and conclude that the origin of penumbral filamentary
structure is overturning convection.
