Spines are a key evolutionary innovation that help plants protect themselves from being eaten. They originate from different plant parts—such as leaves, stems, or branches—in various lineages. Until now, systematic studies of how spiny plants are distributed across global environmental gradients have been limited.
In a study published in Biological Review, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences found that spiny species are more prevalent in dry climates, certain soil types, and regions historically rich in large mammalian herbivores. The research, which analyzed distribution data of woody plants from China, South Africa, and Australia, combining climate, soil, and paleo-herbivore data, provides broad-scale evidence that plant defences are shaped by both environmental conditions and pressure from herbivores.
The researchers used a spatial mode analysis approach to investigate the macroecological characteristics of thorns on woody plants. They explored the important ecological innovation role of thorns in plant defense and diversity, as well as the diversity of thorn types and anatomical structures in different environmental gradients. They also analyzed the possible impact of climatic and soil attributes on the diversity of spiny plants, and investigated the spatial pattern of species richness of spiny woody plants in different regions.
They found that approximately 12% of woody plant species across the three continents bear spines, though the proportion varies regionally—from 9% in South Africa to 15% in China. The proportion of spiny plants increases in drier areas and soils with higher clay content, but decreases in nitrogen-rich soils.
Different spine types—such as thorns, prickles, and spines—are distributed differently across climate and soil gradients, suggesting trade-offs and specializations under varying environmental conditions.
Moreover, spatial patterns of spiny plant diversity were positively correlated with the estimated historical richness of large herbivorous mammals (over 20 kg in body size), supporting the hypothesis that mammalian herbivory has been a major driver of spine evolution.
“We’ve long suspected that spines help plants resist herbivory, especially in areas with high pressure from large mammals. But it was striking to see how consistently spiny plant richness correlated with historical mammal richness and environmental factors like aridity and soil properties,” said Kyle W. Tomlinson of XTBG.
First published: 06 August 2025
