Abstract: INTRODUCTION: The superhydrophobic structures on plant leaves are crucial for self-cleaning and anti-microbial functions, acting as both a core functional mechanism and a biomimetic blueprint for advanced materials design. Ferns, as the earliest vascular plants that transitioned from aquatic to terrestrial habitats, have evolved a remarkable diversity of these water-repellent structures, offering unique insights into their evolutionary adaptations. However, systematic studies on the hydrophobic mechanisms and adaptive significance of ferns remain relatively scarce.


  RATIONALE: To elucidate the structural basis, ecological relevance, and evolutionary trajectory of superhydrophobicity in ferns, we combined literature review and preliminary observations to select 25 fern species for detailed analysis of leaf epidermal micromorphology. Among these, 20 species exhibiting notable hydrophobic properties were further investigated to quantify their surface wettability and correlate microstructure with function. We integrated habitat preference data and phylogenetig reconstructions based on chloroplast genomes to examine the potential influence of environmental factors and evolutionary history on the development of hydrophobic traits.

  RESULTS: Our investigations revealed that leaf hydrophobicity in ferns is closely associated with surface microstructure. Most hydrophobic species displayed hierarchical structures comprising polygonal protrusions and epicuticular wax crystals, with a contact angle exceeding 130° serving as a reliable indicator of significant hydrophobicity. Habitat correlation analysis indicated that species endemic to humid or water-rich environments exhibited more pronounced hydrophobic properties. Furthermore, phylogenetic reconstruction demonstrated that superhydrophobicity evolved independently multiple times during fern diversification, suggesting convergent adaptation to specific ecological conditions.

  CONCLUSION: Leaf hydrophobicity in ferns correlates directly with surface microstructure complexity, exhibiting unique multi-scale hierarchical organizations. Notably, a contact angle exceeding 130° already induces distinct hydrophobicity in ferns—lower than the conventional 140° threshold for superhydrophobicity. Species from humid habitats show enhanced water repellency, supporting superhydrophobicity as an evolutionary adaptation to environmental constraints. These findings advance the theoretical framework for plant surface hydrophobicity and provide biomimetic design principles for functional materials. Future studies should examine wax chemistry, ecological factors, and soral structures to further elucidate hydrophobic mechanisms.
  An overview of hydrophobicity in ferns: SEM observation and contact angle measurement were conducted on the leaf epidermis of ferns, revealing that superhydrophobic characteristics have independently evolved multiple times in this plant group.  

Key words: Ferns, leaf micromorphology, superhydrophobicity, ecological adaptation, phylogeny, biomimetics