I found a mention of Bérenger on the web in a digitized (by Google) book, Chapel Hill (1996) by James Vickers, a history of the town (where I went to school) in North Carolina with an illustration (on p. 38) reproducing a page from from the Fall 1860, Spring 1861, rose catalog of Thomas Paxton, Florist. Bérenger is listed therein as a rosy lilac Hybrid Perpetual that occasionally repeated. The book relates that Paxton was an Englishman who arrived in North Carolina in 1851 as campus gardener and caused a scandal the following year by marrying the 15-year-old housemaid of the family in whose home he resided. Quote: His nursery,here advertised in the the last months of peace, clearly specialized in the roses that abounded in Chapel Hill and that would soon provide the raw material for R.B. Saunders' Blue Mass. End Quote.
R.B. Saunders was a local pharmacist who concocted a purgative used in the Civil War (and earlier), containing rose petals gathered by the ladies of Chapel Hill; honey; and mercury. Along what strange byways the search for lost roses leads.