One fungus is not like the other. Fungi vary largely in color, size, shape, texture, smell, habitat, manner of growth, and many other ways.
However, little has been done in the way of classifying fungi as a kingdom. Fungi experts estimate that there are as many as one million to 1.5 million species of fungi, but that we've identified and named only about ten-percent of them.
Understanding how different species of fungi are related is important because some fungi are used to treat diseases, while others cause diseases or are poisonous. If you can't tell one fungus from another, you could make a fatal mistake. Also, if scientists can identify a species closely related to a fungus used as a treatment for disease, then they can examine it for the same potential.
Take the porcini mushroom, for example. Porcinis have long been used as medicine, most recently to treat cancer. It was long assumed that there was merely one, maybe two, species of porcinis, but now we know there are at least thirty-five species. So do all porcinis destroy tumor cells or just some species? Wouldn't you like to know the answer before your cancer was treated with just any random porcini?
That's why scientists are now working to piece together the fungi family tree. To do this, they're examining the various features of fungi, such as those mentioned, color, shape, smell, and so on. They're also comparing the DNA of different species in order to figure out how closely or distantly they're related. Maybe one day we'll know as much about the relationships among fungi and the evolution of fungi as we know about animals.