First of all, limes and lemons taste differently; limes have a bitter taste while lemons have a sour one. Limes are green and almost round in shape while lemons are yellow and oval-shaped. Limes are smaller, too. Some think that limes are immature lemons but this is not the case. Limes turn yellow if they stay on the tree longer but do not become lemons. However, despite all these differences, nutritionally they are almost the same and they can perfectly substitute for each other in a recipe.