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Flora Italiana (http://floraitaliana.blogspot.co.uk/) gives four species of Centranthus and a subspecies growing in Italy, namely:
Centranthus ruber subsp. ruber.
C. ruber is found throughout Italy. The only other species growing that far north is C. angustifolius.
Mark's safe option seems best.
Centranthus ruber is the only one recorded from the Lake Garda region (http://luirig.altervista.org/flora/taxa/floraspecie.php?genere=Centranthus).
Many thanks to one and all.
Lat/Lng: 45.821, 10.779