Exploring leaf morphology of Parablechnum cordatum complex (Blechnaceae): An outline analysis approach using Elliptic Fourier Analysis for taxonomic resolution

Parablechnum is a genus in the fern family Blechnaceae that exhibits wide morphological variation without a distinct taxonomic discontinuity. To address this problem, we applied the technique of Elliptic Fourier Analysis to evaluate leaf shape by calculating Fourier harmonics based on coordinates derived from a closed outline. Using a combination of contour extraction software and the Momocs package in R, it was possible to analyze 102 specimens of Parablechnum using the pinna as the analytical component, due to its ease of visualization in digitized herbarium specimens. Among the six studied species, three distinct groups were identified using LDA and PCA, with one group consisting exclusively of Parablechnum cordatum. This analysis reaffirmed the segregation found in other studies, helped resolve the P. cordatum complex. This technique enables the use of digitally available herbarium materials, offering the possibility of identifying old specimens and evaluating taxonomic variation in cases like Parablechnum.

Keywords:
Elliptic Fourier Analysis; fern analysis; fern taxonomy; morphometrics