We consider the group theoretical properties of R--R scalars of string theories in the low-energy supergravity limit and relate them to the solvable Lie subalgebra _s⊂ U of the U--duality algebra that generates the scalar manifold of the theory: [_s]= U/H. Peccei-Quinn symmetries are naturally related with the maximal abelian ideal A⊂_s of the solvable Lie algebra. The solvable algebras of maximal rank occurring in maximal supergravities in diverse dimensions are described in some detail. A

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... icular example of a solvable Lie algebra is a rank one, 2(h_2,1+2)--dimensional algebra displayed by the classical quaternionic spaces that are obtained via c-map from the special Kählerian moduli spaces of Calabi-Yau threefolds.