International audienceThe use of moss material to make boats watertight (caulking) has been a widespread practice in Europe, with records dating back to the Bronze Age. In this article we report the bryophyte assemblages from fifteen boats, which have been conserved as wrecks in the rivers of Upper Rhne and Sane near Lyons, France. The assemblages vary according to their composition, with Neckera crispa Hedwig being one of the dominant species overall. Following ancient technical descriptions we performed experimental collections from bark and rocks in the Jura Mountains. Comparing these to the archaeological records revealed that most of the mosses were probably of bark origin and were collected in base rich areas. Our data is discussed in the context of archaeological caulking in Western Europe. While in much of Europe N. crispa strongly decreased as a caulking material from the 14th century onwards, it remained much used in our study area. This is probably due to the persistence of suitable forests in the Jura mountains

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