Elucidating the Stem of Crassulaceae: A Structural Chemical-Anatomical Analysis

Crassulaceae comprises succulent species characterized by extensive water-storage tissues and considerable anatomical diversity, yet comparative information on the chemical composition and structural organization of their stem cell walls remains limited. This study characterized stem cell-wall composition and anatomy in 33 Crassulaceae species using sequential extraction, lignocellulosic fractionation, Fourier-transform infrared spectroscopy (FTIR), epifluorescence microscopy, and multivariate analyses. Significant interspecific differences were detected in extractives, lignin, cellulose, hemicellulose, the semiquantitative FTIR-derived syringyl-to-guaiacyl spectral index (S/G index), and cellulose structural indices. Principal component analysis revealed complementary gradients associated mainly with the hemicellulose-cellulose balance, lignin content, and cellulose organization, whereas PERMANOVA indicated significant multivariate differentiation among genera. Partial least squares discriminant analysis showed moderate genus-level discrimination and identified the total crystallinity index (TCI), lateral order index (LOI), and FTIR-derived S/G index as the variables contributing most consistently to genus differentiation. Anatomically, cell-wall components were heterogeneously distributed among tissues, with lignified secondary walls primarily associated with xylem vessels, fibers, and lignified parenchyma when present, whereas nonlignified cellulosic walls predominated in cortical and pith parenchyma. Differences were also observed in periderm organization and in the distribution of phenolic-rich cellular contents. Together, these results demonstrate substantial chemical, spectroscopic, and anatomical diversity in Crassulaceae stems and indicate that variation in cell-wall traits is partially structured among genera. This comparative framework provides a basis for future studies evaluating the functional, ecological, evolutionary, and applied significance of stem cell-wall diversity in succulent plants.