  We define new combinatorial objects, called shrubs, such that forests of
rooted trees are shrubs. We then introduce a structure of operad on shrubs. We
show that this operad is contained in the Zinbiel operad, by using the
inclusion of Zinbiel in the operad of moulds. We also prove that this inclusion
is compatible with the richer structure of anticyclic operad that exists on
Zinbiel and on moulds.
