  A k-dimensional box is the Cartesian product R_1 x R_2 x ... x R_k where each
R_i is a closed interval on the real line. The boxicity of a graph G, denoted
as box(G) is the minimum integer k such that G is the intersection graph of a
collection of k-dimensional boxes. Halin graphs are the graphs formed by taking
a tree with no degree 2 vertex and then connecting its leaves to form a cycle
in such a way that the graph has a planar embedding. We prove that if G is a
Halin graph that is not isomorphic to K_4, then box(G)=2. In fact, we prove the
stronger result that if G is a planar graph formed by connecting the leaves of
any tree in a simple cycle, then box(G)=2 unless G is isomorphic to K_4 (in
which case its boxicity is 1).
