DEVELOPMENT OF A NEW CHEMICAL METHOD FOR DISTINGUISHING BETWEEN BETULA-PENDULA AND BETULA-PUBESCENS IN SWEDEN

High performance liquid chromatography (HPLC) analytical studies of in ner bark extractives from a large number of silver birch (Betula pendu la Roth) and hairy birch (Betula pubescens Ehrh.) trees revealed the d iarylheptanoid glucoside platyphylloside to be present at high levels in B. pendula (20-60 mg/g dry bark) and at low levels in B. pubescens (less than or equal to 0.5 mg/g dry bark). Based on these observations , a new simple and accurate precipitation method to distinguish betwee n B. pendula and B. pubescens has been developed. In a solution of 2,4 -dinitrophenylhydrazine, platyphylloside immediately forms an orange p recipitate. 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 sol ution. However, no precipitate forms when a sample from B. pubescens i s used. The diagnostic value of morphological characters was assessed by comparing the results of species determinations made on a large num ber of trees (>1600), both juvenile and mature, using the morphologica l and the new chemical method. For birches younger than 20 years there was 100% agreement between the two methods. However, in some mature b irch stands with the two species mixed and ages over 40 years, up to 2 0-30% of the trees were incorrectly identified to species using morpho logical characters. Results from tests using the precipitation method on birch species, varieties, forms, and hybrids were reported.