The single specimen used by an author to name a taxon; the type specimen; a type material recognized by the International Code of Nomenclature for algae, fungi, and plants (ICN).
The author of the taxon designates this specimen as a type according to the ICN.
The ICN uses a system called typification that makes objective identification possible by linking a name with an actual specimen. Typification is intended to create a stable system of nomenclature by tying the published name to a specimen or a suite of specimens. Note that, for diatoms, a slide may be designated as a holotype, rather than a single specimen. Although this practice is permitted within the ICN, it is not encouraged because confusion could arise later regarding the intent of the author.
Several other kinds of type material are recognized by the ICN, including isotype, lectotype, neotype and paratype. Types are not expected to be “typical” or “idealized” specimens, although workers may find such use of the terms.
McNeill J., Barrie, F.R., Buck, R., Demoulin, V., Greuter, W., Hawksworth, D.L., Herendeen, P.S., Knapp, S., Marhold, K., Prado, J., Prud'homme Van Reine, W.F., Smith, G.F., Wiersema, J.H. (2012). International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) . Regnum Vegetabile 154. ISBN 978-3-87429-425-6. http://www.iapt-taxon.org/nomen/main.php
Winston, J.E. (1999). Describing Species: A Practical Taxonomic Procedure for Biologists. Cambridge University Press, Cambridge, 518 pp.