Phenological growth stages of Xanthoceras sorbifolium Bunge: Codification and description according to the BBCH scale

Xanthoceras sorbifolium Bunge is a kind of unique oil tree species found in northern China that has high ecological, ornamental, and economic value. Its seed oil is not only a high-quality edible oil well supplied with unsaturated fatty acids but also a superior raw material for biodiesel production. In the present study, the different phenological growth stages of X. sorbifolium were characterized according to the Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie (BBCH) scale. Eight principal growth stages were described for the bud, leaf and shoot development; inflorescence emergence and flowering; fruit development and maturity, together with senescence and beginning of dormancy. Meanwhile forty-two secondary growth stages were described in detail. Illustrative pictures with a codification were provided to better define and describe these phenological growth stages. Phenological records from two growing seasons were used to create a schematic representation of the principal growth stages. This study provides a beneficial reference for general orchard management, scientific research, and cultivation of new cultivars.