## 2 Results
### Morphological Characterization of Glandular and Non-Glandular Trichomes of T. sinensis  
To further understand the morphological structure of trichomes, we studied the trichomes of _T. sinensis_ leaves using scanning electron microscopy and laser confocal microscopy. By real-time imaging confocal laser microscopy, we observed two unique trichomes: one is a typical hair-like structure with UV-excited autofluorescence and is non-glandular; the other is an epidermal trichome with weak autofluorescence signal at the base (Figure 2b), and this trichome is composed of multiple cells and has an oval shape (Figure 2a). To further characterize the morphology of trichomes, we performed an SEM analysis. We found that _T. sinensis_ has at least three types of trichomes: sessile glandular, stalked glandular, and non-glandular trichomes, which differ greatly in morphology, structure, and cellular composition (Figure 2c). We found that both the non-glandular trichomes and glandular trichomes of _T. sinensis_ were attached to the leaf epidermis, which might have developed directly from leaf epidermal cells. The non-glandular trichomes were typical unicellular trichomes, which were needle-like and had no basal cells (Figure 2b,c), and the length of the developed mature non-glandular trichomes observed by laser microscopy could reach 456 \(\upmu\)m (Figure 2b). The stalked glandular trichomes were generally elliptical in shape (Figure 2a,c) and had a multicellular tower-like arrangement morphology with 2-3 basal cells at the base and 6 layers of cells arranged to form the head at the top (Figure 2a,d). Sessile glandular trichomes are shorter than stalked glandular trichomes, may be composed of single cells, and have a significant head space area, indicating that they may be storage sites for volatiles (Figure 2c). Compared with the non-glandular trichomes, the glandular trichomes were shorter, with distinct nuclei and other organelles in the apical and middle cells, suggesting that they may have an active function in the synthesis of secondary metabolites. Figure 1: Variation in trichome density in _T. sinensis_ and distribution pattern of geographical origins. (**a**) Based on the variation in trichome density on the leaves of _T. sinensis_, the breeding populations were grouped into five types. Representative leaves (abaxial surface) were visualized using light-dissection microscopy. (**b**) Distribution of different categories of germplasms using the breeding population of 187 individuals. (**c**) Geographical origin of the category I varieties. (**d**) Geographical origin of the category II–V varieties. Changes in the Distribution of Epidermal Trichomes and Differences in Their Volatile Substances Among Varieties of T. sinensis  
To investigate the relationship between epidermal trichomes and volatile components, we examined two typical varieties, CAF0845 (type-I) and CAF0830 (type-V), with significant differences in the epidermal trichome density (Figure 3a). We performed SEM analyses on three representative regions (apical, middle, and basal) of the adaxial and abaxial surfaces of young leaves in each variety, respectively. We observed that the number of trichomes in the apical region was the lowest in both species (Figure 3b,c), and only a small number of predominantly non-glandular trichomes were observed at the dorsal tip of CAF0830 (Figure 3c). Based on the SEM analysis, the CAF0830 variety has more trichomes in all the corresponding regions than the CAF0845 variety (Figure 3b,c); however, both varieties have a large number of glandular and non-glandular trichomes in the central region, especially the distal axial surface which is predominantly glandular trichomes (Figure 3c). To statistically analyze the differences in trichomes between the two varieties, we compared the number of glandular and non-glandular trichomes on the adaxial and abaxial surfaces of the middle region of leaves.