Lichens pose a problem for biological classification, because the three types of organism concerned come from three different kingdoms. After long debate, lichen are now classified as fungi, under the genus and species of the host fungus. This allows specimens to be put into boxes and labelled. By having specific names, researchers know what they are working on: that is one of the basic functions of taxonomy. The system still has its problems. In those fungi which may associate either with an alga, or with a cyanobacterium, the resulting forms (called "photomorphs") may look quite different, yet are now referred to by the same name.