  Elemental 2D materials exhibit intriguing heat transport and phononic
properties. Here we have investigated the lattice thermal conductivity of newly
proposed arsenene, the 2D honeycomb structure of arsenic, using {\it ab initio}
calculations. Solving the Boltzmann transport equation for phonons, we predict
a highly anisotropic thermal conductivity, of $30.4$ and $7.8$ W/mK along the
zigzag and armchair directions, respectively at room temperature. Our
calculations reveal that phonons with mean free paths between $20$ nm and $1$
$\mu$m provide the main contribution to the large thermal conductivity in the
zig-zag direction, mean free paths of phonons contributing to heat transport in
the armchair directions range between $20$ and $100$ nm. The obtained low and
anisotropic thermal conductivity, and feasibility of synthesis, in addition to
other reports on high electron mobility, make arsenene a promising material for
a variety of applications, including thermal management and thermoelectric
devices.
