According to the Angiosperm Phylogeny Group (APG), the Brazil nut family belongs to the order Ericales which is basal to the euasterid clade.    From Wordnik.com.  [Brazil nut family (Lecythidaceae) in the New World] Reference

Within the Ericales, the position of the Lecythidaceae is not resolved.    From Wordnik.com.  [Brazil nut family (Lecythidaceae) in the New World] Reference