Distribution patterns of glandular trichomes in the flora of the Hengduan Mountains, southwestern China

Glandular trichomes are traditionally regarded as a defence against insect herbivores in plants. A comprehensive examination of their occurrence across an entire flora is essential for understanding how plant-herbivore interactions influence species abundance, traits, and diversity. In this study, we gathered data on the presence of glandular trichomes in a diverse flora comprising 7751 angiosperm species from the Hengduan Mountains region in southwestern China, testing the effects of plant organ, life form, leaf habit, phylogenetic position, and geographical element on the occurrence of glandular trichomes. Our results showed that 1021 species (13.2%) in the studied flora possessed glandular trichomes. Reproductive organs (88.0%) displayed a significantly higher occurrence of glandular trichomes compared to vegetative organs (59.1%). Within flowers, the calyx (81.1%) was the most defended, followed by the corolla (17.4%), and the gynoecium (12.5%). The androecium (1.8%) was the flower component least associated with glandular trichomes. Herbaceous species (14.0%) were more likely to have glandular trichomes than woody species (11.6%). For woody plants, leaf habit (deciduous/evergreen) had no significant effect on the presence of glandular trichomes on leaf blades, but had a significant effect on the occurrence of glandular trichomes on reproductive organs, with deciduous woody species (11.0%) displaying a higher prevalence compared to evergreen woody species (8.3%). Interestingly, the proportion of species with glandular trichomes was notably lower in the tropical elements (6.8%) compared to both temperate and cosmopolitan elements (15.3% and 15.6%, respectively). Our findings suggest that in the Hengduan Mountains region, the evolution of glandular trichomes exhibits distinct patterns among various life forms, plant organs, leaf habits, and geographical elements, while showing limited influence from phylogenetic relatedness, highlighting the remarkable evolutionary adaptability of this defensive plant trait.