Horizontal submanifolds of groups of Heisenberg type
  We study maximal horizontal subgroups of Carnot groups of Heisenberg type. We classify those of dimension half of that of the canonical distribution ("lagrangians") and illustrate some notable ones of small dimension. An infinitesimal classification of the arbitrary maximal horizontal submanifolds follows as a consequence. 
A. Kaplan, F. Levstein, L. Saal and A. Tiraboschi