Abstract
Spinescence has been thought to have evolved mainly as a defense against herbivores. Thus, studying its evolution in a whole flora is an excellent approach for understanding long-term plant-herbivore interactions. In this study, we characterized the spinescent plant species of Jiaozi Snow Mountain, Southwestern China, in order to explore the effects of life forms, plant organs, phylogenetic position, and phytogeographical origin on spinescence occurrence. The Jiaozi Snow Mountain flora includes 137 spinescent species (9.2%) out of 1488 angiosperm species. We found that in these spinescent species, vegetative organs (70.0%) were significantly more defended than reproductive organs (43.8%). Life form had a significant effect on spinescence occurrence. Woody species (18.6%) were more likely to be spiny than non-woody species (6.4%); moreover, woody species mostly defend their vegetative organs (92.2%), whereas herbaceous species mostly defend their reproductive organs (73.3%). For woody plants, leaf habit has a significant effect on spinescence. Specifically, spinescence was more common on the reproductive organs of deciduous woody species than on those of evergreen woody species; furthermore, spinescence was more common on the leaf blades of evergreens than on those of deciduous species; however, the proportion of spinescent petioles in deciduous species was significantly higher than in evergreens. The most common spine color was yellow (40.8%), followed by white (16.8%), red (15.8%), and brown (14.3%); furthermore, 74.4% of spinescence that showed aposematic color was a different color than the plant organ on which grown. These findings suggest that spinescence is visually aposematic in the Jiaozi Snow Mountain flora. Phylogenetically, more families tended to have spines on vegetative organs (83.3% in vegetative organs, 50.0% in reproductive organs), but the phylogenetic signals were weak. The proportion of spinescence was not significantly different between tropical (9.8% of genera, 7.6% of species) and temperate (13.2% of genera, 9.5% of species) elements. These results indicate that in the Jiaozi Snow Mountain flora spinescence evolved differently in various life forms and plant organs, but that these differences were not influenced by phylogenetic position or phytogeographical origin.