In this paper we give sharp extension results for convoluted solutions of abstract Cauchy problems in Banach spaces. The main technique is the use of algebraic structure (for usual convolution product * ) of these solutions which are defined by a version of the Duhamel formula. We define algebra homomorphisms from a new class of test-functions and apply our results to concrete operators. Finally, we introduce the notion of k-distribution semigroups to extend previous concepts of distribution semigroups.2010 Mathematics Subject Classification. Primary 47D62, 47D06; Secondary 44A10, 44A35 . Key words and phrases. Abstract Cauchy problem; convoluted semigroups; Laplace transform, distribution semigroups. P.J.