Ulva and Enteromorpha are two of the most common important genera of green seaweeds grow along the Mediterranean seashore of Alexandria. They are widely regarded as easily distinguishable genera because of their different morphologies. Randomly amplified polymorphic DNA-PCR, protein profile, infrared spectroscopy of total lipids and absorption spectra of pigments were used to determine phylogenetic relationships among these taxa. The similarity matrixes were used to calculate genetic distances for out grouping the studied species. Data showed that both bladelike and tubular morphologies can occur even with groups exhibiting very little sequence divergence. The switch between blade and tube morphology happens in populations under natural conditions and has occurred at various times throughout the evolutionary diversification of the Ulva and Enteromorpha species.