  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 $\IG_s\subset U$ of the U--duality algebra that generates the
scalar manifold of the theory: $\exp[\IG_s]= U/H$. Peccei-Quinn symmetries are
naturally related with the maximal abelian ideal ${\cal A} \subset \IG_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
particular 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 K\"ahlerian moduli spaces
of Calabi-Yau threefolds.
