An assessment of aspect ratio and length–width probability region based on linear leaf dimensions in Sargassum: determining the extent of variation

The cosmopolitan brown algal genus Sargassum poses challenges for classifying the taxa at an appropriate taxonomic level. We studied the a leaf morphometry of Sargassum spp. from Indian waters, to find: (1) if there exists a difference in aspect ratio in leaves of different species; (2) the Length–Width Probability Region (LWPR) for various species; and (3) the extent of variation in the herbarium and fresh collection respectively. The assessment of leaf aspect ratio using secondary data, herbarium and freshly collected samples revealed species wise differences. Analysis depicted the species specific aspect ratio differences ranging from 0.85 (in S. grevillea) to 50 (in S. filifolium). S. icilifolium, S. tenerimum and S. vulgare registered the broadest LWPR compared to other species with an area of 442.74 mm² (R² = 0.649, N = 196), 366.95 mm² (R² = 0.638, N = 529) and 256.65 mm² (R² = 0.734, N = 243), and an angle of inclination, 19.03°, 13.92° and 10.03°, respectively. We introduced a simple, non-cumbersome and low skill set based technique for species differentiation in inventories. Multiple regression analysis depicted S. johnstonii as the most statistically significant species across the datasets investigated. Further, efforts incorporating a larger sample size from a wide range of geographical locations are crucial for assessing the efficiency of the method.