Application of scanning electron microscopy unraveling seed micromorphological characteristics in laticifers of family Apocynaceae and subfamily Asclepiadoideae

The understanding of trait variation within the seed collection provides an understanding of genetic variation and knowledge about plant conservation. In this study, twelve species of the lactiferous family Apocynaceae and subfamily Asclepiadoideae have been evaluated for seed macro-micromorphological characterization. Seed surface texture, dimension, seed shape and sculpture, seed wing surface cell, coma position, level and color, hilum position and shape were examined by using a scanning electron microscope (SEM). This is the first study reporting coma surface sculpturing in Pakistan. Qualitative and quantitative features of seeds exhibited alteration among selected species of both families. The seed shapes were found oblong and flattened. Eight types of seed coat surface (reticulate-regular, reticulate-irregular, regular-rugose, aculeate, papillate, reticulate, ruminate, and striate), nine types of seed wing sculpturing, and four types of hilum surface cells that varied from reticulate to striate were observed. The maximum number of seed surfaces exhibited spiral to undulate hairy anticlinal wall ornamentation. The periclinal wall varied from smooth to warty. A taxonomic key was developed using seed morphological characters for the correct identification of lactiferous taxa. The variations among the studied species described the significance of SEM as a beneficial tool to vitalize the hidden micromorphological features among seeds of lactiferous taxa that eventually aid in seeds' accurate identification, delimitation, classification, and exploration in the future. Laticifer features are useful to understand the generic relationships within the family.