  We present a bijection from planar reduced trees to planar rooted hypertrees,
which extends Knuth's rotation correspondence between planar binary trees and
planar rooted trees. The operadic counterpart of the new bijection is
explained. Related to this, the space of planar reduced forests is endowed with
a combinatorial Hopf algebra structure. The corresponding structure on the
space of planar rooted hyperforests is also described.
