Traditionally, type specimens have not been deposited for most unicellular algae. There are few known holotypes and those that are available are often of limited use. Samples from taxa described before 1900 commonly consist of materials dried down on herbarium sheets or mica. Dried algal samples can be rehydrated, but preservation is very poor and little structure can be determined from them. Whether wet or dry, the amount of information that can be derived from such samples using conventional light microscopy is limited.