The initial state is a pseudostate (see Abschnitt 20.11, „Pseudostate“) representing a source for a single transition to the default state of a composite state. It is the state from which any initial transition is made.
As a consequence it is not permissible to have incoming transitions. ArgoUML will not let you create such transitions, and if you import a model that has such transitions, a critic will complain.
There can be at most one initial pseudostate in a composite state, which must have (at most) one outgoing transition.
An initial state is represented on the diagram as a solid disc.