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The Evolutionary Significance of Leaf Nodulation: Evidence from Ardisia and Its Relatives (Primulaceae: Myrsinoideae)
by
, , ,
Dan Wei
1
,
Tong-Jian Liu
2,3,
Xiao-Kai Yan
4,
Xing-Feng Wang
2,3,
Ge-Han Huang
5,
Yuan Xu
2,3,
Xing Wu
3,
Xue-Jun Ge
2,3,
Gang Hao
1,* and
Hai-Fei Yan
2,3,* 1
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China
2
State Key Laboratory of Plant Diversity and Specialty Crops, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
3
South China National Botanical Garden, Guangzhou 510650, China
4
Guangdong Nanyue Ecological Technology Co., Ltd., Guangzhou 510500, China
5
Suzhou Customs, Suzhou 215028, China
*
Authors to whom correspondence should be addressed.
Biology 2026, 15(17), 1451; https://doi.org/10.3390/biology15171451
Submission received: 2 July 2026
/
Revised: 15 August 2026
/
Accepted: 19 August 2026
/
Published: 24 August 2026
Simple Summary
Leaf nodule symbiosis, a unique bacterial association occurring in the phyllosphere microbiome, has been shown to influence host growth, immune responses, and secondary metabolism, suggesting its potential role in promoting evolutionary radiations. Nevertheless, direct macroevolutionary evidence linking this symbiosis to lineage diversification has remained scarce. In this study, we used Ardisia, a lineage characterized by typical leaf nodulation, to test this hypothesis. We reconstructed a robust phylogenetic framework based on plastid genomes, nrDNA, and genome-wide single nucleotide polymorphism (SNP) datasets. We resolved several longstanding phylogenetic uncertainties within Ardisia and its allies, including the placement of Sadiria, Tapeinosperma, Amblyanthus, and Amblyanthopsis, and revealed a middle Miocene rapid radiation in Ardisia and its allies. Importantly, we demonstrate that the origin of leaf nodule symbiosis coincided temporally with this radiation (~11–8 Ma). Diversification analyses further show that leaf-nodulated lineages exhibit significantly elevated speciation rates, suggesting that leaf nodule symbiosis may represent a key evolutionary innovation driving diversification.
Abstract
Interactions between plants and microorganisms have long been a central topic in biological research. Bacterial symbiosis on leaf surfaces represents a distinctive and mutually beneficial system within the phyllosphere microbiome. Leaf nodules are the visible manifestation of the symbiosis and confer ecological advantages to host plants by enhancing host resistance against pathogens and herbivores. It has been hypothesized that these advantages promote higher diversification rates in host lineages, but this remains uncertain. Ardisia subg. Crispardisia and its close relatives (Amblyanthopsis and Amblyanthus) within Primulaceae are typical plant groups with leaf nodule symbiosis, making them an ideal system for testing this hypothesis. In this study, we conducted extensive sampling of “Ardisioids” (Ardisia and its allies) and reconstructed their phylogenetic relationships and evolutionary history using plastid genomes and nuclear datasets (i.e., nuclear ribosomal DNA (nrDNA) and genome-wide single nucleotide polymorphisms (SNPs)). We clarified the phylogenetic positions of several “Ardisioids” genera (e.g., Sadiria, Tapeinosperma, Amblyanthus, and Amblyanthopsis) and multiple subgenera within Ardisia. We further detected a rapid radiation during the middle Miocene in Ardisia and its allies. Notably, we found that the leaf-nodulated clade appears to have originated during this period, approximately 11–8 Ma. BAMM (Bayesian Analysis of Macroevolutionary Mixtures) analyses revealed elevated diversification rates in leaf-nodulated lineages, while HiSSE (Hidden State Speciation and Extinction) analyses indicated that leaf nodule symbiosis might have increased speciation rates without significantly affecting extinction rates. These results provide strong evidence that leaf nodule symbiosis, together with other abiotic and biotic factors, represents a key evolutionary innovation that has promoted diversification in Ardisia and its close relatives.
Keywords:
phyllosphere microbiome; leaf nodule; symbiosis; diversification rate
