WEBMar 14, 2024 · Physical description. Bark of the paper birch (Betula papyrifera). Sweet birch (Betula lenta). A birch has smooth, resinous, varicoloured or white bark, marked by horizontal pores (lenticels), which usually peels horizontally in thin sheets, especially on young trees. On older trunks the thick, deeply furrowed bark breaks into irregular plates.