Chemical constituents in leaves of Magnolia officinalis var. biloba Analysis on chemical constituents of volatile oil in Magnolia officinalis var. biloba produced in Jinggangshan Identification of 1-deoxy-D-xylulose-5-phosphate synthase and analysis on essential oil in Magnolia officinalis Distinguishing Magnolia officinalis from its imitation Ilex rotunda by UV spectrophotometry