  The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are
the general scheme of scalar-tensor theories allowing the possibility for
realizing the tensor propagation speed $c_t$ equivalent to 1 on the isotropic
cosmological background. We propose a dark energy model in which the late-time
cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the
ghost condensate with cubic and quartic Galileons in the framework of GLPV
theories. We show that a wide variety of the variation of the dark energy
equation of state $w_{\rm DE}$ including the entry to the region $w_{\rm
DE}<-1$ can be realized without violating conditions for the absence of ghosts
and Laplacian instabilities. The approach to the tracker equation of state
$w_{\rm DE}=-2$ during the matter era, which is disfavored by observational
data, can be avoided by the existence of a quadratic k-essence Lagrangian
$X^2$. We study the evolution of nonrelativistic matter perturbations for the
model $c_t^2=1$ and show that the two quantities $\mu$ and $\Sigma$, which are
related to the Newtonian and weak lensing gravitational potentials
respectively, are practically equivalent to each other, such that $\mu \simeq
\Sigma>1$. For the case in which the deviation of $w_{\rm DE}$ from $-1$ is
significant at a later cosmological epoch, the values of $\mu$ and $\Sigma$
tend to be larger at low redshifts. We also find that our dark energy model can
be consistent with the bounds on the deviation parameter $\alpha_{\rm H}$ from
Horndeski theories arising from the modification of gravitational law inside
massive objects.
