"Morphological differences" refer to variations or distinctions in the physical characteristics or structure of something, such as the shape, size, or form of an object or organism. Full definition
Biologists have long recognized morphological differences between Africa's forest - dwelling elephants and those that inhabit the savanna. (scientificamerican.com)
Matsuura identified the fish on the basis of morphological differences too obscure for anyone but an expert to discern: the pattern of prickles on their backs. (discovermagazine.com)
At UMass, Gwiazdowski and Normark looked at genetic variation using genes throughout the genome, while at the AMNH Vea looked for morphological differences in specimens mounted on microscope slides. (sciencedaily.com)