Development of a new chemical method for distinguishing between <i>Betula</i><i>pendula</i> and <i>Betula</i><i>pubescens</i> in Sweden

Abstract

High performance liquid chromatography (HPLC) analytical studies of inner bark extractives from a large number of silver birch (Betulapendula Roth) and hairy birch (Betulapubescens Ehrh.) trees revealed the diarylheptanoid glucoside platyphylloside to be present at high levels in B. pendula (20–60 mg/g dry bark) and at low levels in B. pubescens (≤ 0.5 mg/g dry bark). Based on these observations, a new simple and accurate precipitation method to distinguish between B. pendula and B. pubescens has been developed. In a solution of 2,4-dinitrophenylhydrazine, platyphylloside immediately forms an orange precipitate. A similar precipitate is also produced when a piece of B. pendula inner bark is kept for 1 h at room temperature in the same solution. However, no precipitate forms when a sample from B. pubescens is used. The diagnostic value of morphological characters was assessed by comparing the results of species determinations made on a large number of trees (&gt; 1600), both juvenile and mature, using the morphological and the new chemical method. For birches younger than 20 years there was 100% agreement between the two methods. However, in some mature birch stands with the two species mixed and ages over 40 years, up to 20–30% of the trees were incorrectly identified to species using morphological characters. Results from tests using the precipitation method on birch species, varieties, forms, and hybrids were reported.