  W.E. Roth (1952) proved that the matrix equation $AX-XB=C$ has a solution if
and only if the matrices $\left[\begin{matrix}A&C\\0&B\end{matrix}\right]$ and
$\left[\begin{matrix}A&0\\0&B\end{matrix}\right]$ are similar. A. Dmytryshyn
and B. K{\aa}gstr\"om (2015) extended Roth's criterion to systems of matrix
equations $A_iX_{i'}M_i-N_iX_{i''}^{\sigma_i} B_i=C_i$ $(i=1,\dots,s)$ with
unknown matrices $X_1,\dots,X_t$, in which every $X^{\sigma}$ is $X$, $X^T$, or
$X^*$. We extend their criterion to systems of complex matrix equations that
include the complex conjugation of unknown matrices. We also prove an analogous
criterion for systems of quaternion matrix equations.
