Let A' be a semisimple algebraic monoid with unit group G. Associated with E is its polyhedral root system (X, 0, C), where X = X(T) is the character group of the maximal torus T c G, $ c X(T) is the set of roots, and C = X(T) is the character monoid of T c E (Zariski closure). The correspondence £-»(A\ O, C) is a complete and discriminating invariant of the semisimple monoid £, extending the w...