Commonly referred to in the US as 'Ludwig Spaeth'.  This and 'Nadezhda' are the lilacs I planted at the first house I owned on Long Island.  Single deep reddish-purple. Mid-season.   Grows 8-12' H x 6-8' W.  Syringa vulgaris 'Andenken an Ludwig Spath'. Zones 3-7.