Microscopic and scanning electron microscope (SEM) observation of trichome

The fresh buds or flowers of two varieties at S3 were sliced and added to distilled water on microscope slides for observation and photography. In addition, we used a scanning electron microscope (SEM) (TM3030Plus, Hitachi, Japan) to observe the arrangement of trichomes on L. japonica bud or flower samples. According to methods outlined by Ning et al. [39], the bud or flower samples (3 mm × 3 mm) were soaked three times in a phosphate buffer solution (pH 7.3) for 1 min, respectively. The samples were then transferred into 2.5% glutaraldehyde solution at 4 °C for > 24 h, and then dehydrated using a series of ethanol (30, 50, 70, 80, 90, 95, 100 and 100%) mixtures at 4 °C for 30 min, respectively, followed by a series of tert-butyl alcohol (70, 80, 90, 100%) mixtures at room temperature for 20 min to remove the ethanol. After being dried in a freeze-drying box (VFD21S) at 4 °C for 30 min, the samples were sprayed with a 12.5–15 nm gold layer and examined/photographed from multiple different perspectives using a scanning electron microscope. This process was repeated three times for each sample, and five sites were selected for imagery acquisition, and the density and length of glandular hairs and non-glandular hairs were measured.