How to Test for Seed Mucilage to Examine an Age-Old Question: A Response to Ladwig and Lucas (2024).

Traits of seeds are far less-studied than those of vegetative plants, despite the importance of this stage in a plant's life cycle. Much research has demonstrated the importance of certain aspects of seed phenotype, including both chemical and physical traits, to survival in the face of biotic and abiotic selective pressures. One trait with demonstrated physiological and defensive functionality is seed mucilage. This persistent hydrogel coating on the surface of the seed is extremely common and found in thousands of species across angiosperms, with many independent evolutionary origins. Despite attention in taxonomic, floristic, ecological, and biomaterial investigations for over a century, and the economic importance of products derived from this mucilage, the trait is often overlooked, and protocols for the labs determining seed mucilage across plants vary. Here, in response to a paper claiming seed mucilage in many new species due to flawed methodology, we lay out specific protocols to determine the presence of mucilage, in an effort to standardize across studies. We hope these methods prove useful in both evaluating the current literature and permit cross-study comparisons to advance the study of this important trait.