  A phylogenetic network is a simplex (or 1-component tree-child) network if
the child of every reticulation node is a network leaf. Simplex networks are a
superclass of phylogenetic trees and a subclass of tree-child networks.
Generalizing the Sackin index to phylogenetic networks, we prove that the
expected Sackin index of a random simplex network is asymptotically
$\Omega(n^{7/4})$ in the uniform model.
