  Let $G$ be a connected complex semisimple Lie group with a fixed maximal
torus $T$ and a Borel subgroup $B \supset T$. For an arbitrary automorphism
$\theta$ of $G$, we introduce a holomorphic Poisson structure $\pi_\theta$ on
$G$ which is invariant under the $\theta$-twisted conjugation by $T$ and has
the property that every $\theta$-twisted conjugacy class of $G$ is a Poisson
subvariety with respect to $\pi_\theta$. We describe the $T$-orbits of
symplectic leaves, called $T$-leaves, of $\pi_\theta$ and compute the
dimensions of the symplectic leaves (i.e, the ranks) of $\pi_\theta$. We give
the lowest rank of $\pi_\theta$ in any given $\theta$-twisted conjugacy class,
and we relate the lowest possible rank locus of $\pi_\theta$ in $G$ with
spherical $\theta$-twisted conjugacy classes of $G$. In particular, we show
that $\pi_\theta$ vanishes somewhere on $G$ if and only if $\theta$ induces an
involution on the Dynkin diagram of $G$, and that in such a case a
$\theta$-twisted conjugacy class $C$ contains a vanishing point of $\pi_\theta$
if and only if $C$ is spherical.

Representation Theory;Symplectic Geometry