Review Algae 2013, 28(1): 1-29 http://dx.doi.org/10.4490/algae.2013.28.1.001 Open Access Taxonomy and nomenclature of the Conjugatophyceae (= Zygnematophyceae) Michael D. Guiry1,* 1AlgaeBase and Irish Seaweed Research Group, Ryan Institute, National University of Ireland, Galway, Ireland The conjugating algae, an almost exclusively freshwater and extraordinarily diverse group of streptophyte green algae, are referred to a class generally known as the Conjugatophyceae in Central Europe and the Zygnematophyceae elsewhere in the world. Conjugatophyceae is widely considered to be a descriptive name and Zygnematophyceae (‘Zygnemophyce- ae’) a typified name. However, both are typified names and Conjugatophyceae Engler (‘Conjugatae’) is the earlier name. Additionally, Zygnemophyceae Round is currently an invalid name and is validated here as Zygnematophyceae Round ex Guiry. The names of orders, families and genera for conjugating green algae are reviewed. For many years these algae were included in the ‘Conjugatae’, initially used as the equivalent of an order. The earliest use of the name Zygnematales appears to be by the American phycologist Charles Edwin Bessey (1845-1915), and it was he who first formally redistrib- uted all conjugating algae from the ‘Conjugatae’ to the orders Zygnematales and the Desmidiales. The family Closte- riaceae Bessey, currently encompassing Closterium and Spinoclosterium, is illegitimate as it was superfluous when first proposed, and its legitimization is herein proposed by nomenclatural conservation to facilitate use of the name. The ge- nus Debarya Wittrock, 1872 is shown to be illegitimate as it is a later homonym of Debarya Schulzer, 1866 (Ascomycota), and the substitute genus name Transeauina Guiry is proposed together with appropriate combinations for 13 species currently assigned to the genus Debarya Wittrock. The relationships between Mougeotia, Mougeotiopsis, Mougeotiella, and Transeauina require further resolution, as do many of the other genera referred to the Conjugatophyceae. Type spe- cies are designated for genera for which no types were formally selected previously. The number of currently described species of conjugating green algae in AlgaeBase is about 3,500, comprising about 10% of all algal species, with about one third of species referred to the Zygnematales and two-thirds to the Desmidiales. A corresponding 10% of all algal names at the species level and below have been applied to conjugating algae, although a large proportion of these are at the infraspecific level. Key Words: Closteriaceae; Desmidiales; desmids; Transeauina; Zygnematales; Zygnematophyceae new class INTRODUCTION The conjugating green algae comprise an almost en- lack centrioles suggesting that any putative flagella were tirely freshwater group of streptophyte organisms many not secondarily lost in the course of evolution. They are of extraordinary beauty. Other than the blue-green and also unique amongst the algae in “internalizing” repro- red algae, they are unique in possessing no flagellated re- duction using a method of exchanging genetic material productive bodies and indeed any flagella at all, and they long known as conjugation (from the Latin verb conju- This is an Open Access article distributed under the terms of the Received February 11, 2013, Accepted February 26, 2013 Creative Commons Attribution Non-Commercial License (http://cre- Corresponding Author ativecommons.org/licenses/by-nc/3.0/) which permits unrestricted * non-commercial use, distribution, and reproduction in any medium, E-mail: [email protected] provided the original work is properly cited. Tel: +353-91-49-2339, Fax: +353-91-52-5005 Copyright © The Korean Society of Phycology 1 http://e-algae.kr pISSN: 1226-2617 eISSN: 2093-0860 Algae 2013, 28(1): 1-29 gare, to unite). This highly specialised reproductive fea- Conjugatophyceae for AlgaeBase (Guiry and Guiry 2013), ture is clearly a homoplasy otherwise known only in some it became apparent that there were unresolved problems groups of bacteria (genetic exchange in these bacteria is associated with the nomenclature of the included algae at via a plasmid) and a phylum of fungi (the Zygomycota). the class, family and genus level, and in the designation of Despite the seemingly advanced character of conjugation types for genera (see Table 1 for summary of classification in the Conjugatophyceae, these algae actually have poor- to generic rank). These essentially nomenclatural diffi- ly differentiated gametes with the cell contents becoming culties have the potential to create taxonomic complica- only slightly modified and generally fusing entirely. The tions now that molecular taxonomy is being increasingly specialised gametes of other algae have not evolved, per- applied to the conjugating algae (see McCourt et al. 2000 haps because there is no necessity for such modifications and Gontcharov 2008 for reviews, Park et al. 1996, Den- as the gametic material is not released and does not have boh et al. 2001, Gontcharov et al. 2003, Hall et al. 2008, to swim to or attract a partner. Kim et al. 2012). In the course of collating published information on the Table 1. A classification of the orders, families and genera of Conjugatophyceae (= Zygnematophyceae) with a list of genera of uncertain place- ment Order / Family Genera Zygnematales Mesotaeniaceae Ancylonema Berggren, Cylindrocystis Meneghini, Geniculus Prescott, Mesotaenium Nägeli, Netrium (Nägeli) Izigshon & Rothe in Rabenhorst, Nucleotaenium Gontcharov & Melkonian, Planotaenium Petlovany & Palmar-Mordvinsteva, Roya West & G. S. West, Spirotaenia Brébisson, Tortitaenia A. J. Brook Zygnemataceae Debarya Wittrock, Lloydina Ahmad & Goldstein, Mougeotia C. Agardh, Mougeotiella T. Yamagishi, Mougeotiopsis Palla, Neozygnema T. Yamagishi, Sangirellum A. K. Mahato & P. Mahato, Sirocladium Randhawa, Sirogonium Kützing, Spirogyra Link, Temnogametum West & G. S. West, Temnogyra I. F. Lewis, Trigonum A. K. Mahato & P. Mahato, Zygnema C. Agardh, Zygnemopsis (Skuja) Transeau, Zygogonium Kützing Desmidiales Closteriaceae Closterium Nitzsch ex Ralfs, Spinoclosterium C. Bernard Desmidiaceae Actinotaenium (Nägeli) Schellenberg, Allorgeia Gauthier-Lièvre, Amscottia Grönblad, Bambusina Kützing ex Kützing, Bourrellyodesmus Compère, Brachytheca Gontcharov & M. Watanabe, Cosmarium Corda ex Ralfs, Cosmocladium Brébisson, Croasdalea Bicudo & Mercante, Cruciangulum D. B. Williamson, Desmidium C. Agardh ex Ralfs, Docidium Brébisson ex Ralfs, Euastridium West & G. S. West, Euastrum Ehrenberg ex Ralfs, Groenbladia Teiling, Haplotaenium Bando, Heimansia Coesel, Hyalotheca Ehrenberg ex Ralfs, Ichtyocercus West & G. S. West, Ichthyodontum A. M. Scott & Prescott, Mateola R. Salisbury, Micrasterias C. Agardh ex Ralfs, Octacanthium (Hansgirg) Compère, Onychonema Wallich, Oocardium Nägeli, Phymatodocis Nordstedt, Pleurotaeniopsis (Lundell) Lagerheim, Prescottiella Bicudo, Raphidiastrum Palamar-Mordvintseva, Sphaerozosma Ralfs, Spinocosmarium Prescott & A. M. Scott, Spondylosium Brébisson ex Kützing, Staurastrum Meyen ex Ralfs, Staurodesmus Teiling, Streptonema Wallich, Teilingia Bourrelly, Tetmemorus Ralfs ex Ralfs, Triplastrum Iyengar & Ramanathan, Triploceras J. W. Bailey, Vincularia K. Fuciková & J. Kastovsky, Xanthidium Ehrenberg ex Ralfs Gonatozygaceae Genicularia De Bary, Gonatozygon De Bary Peniaceae Penium Brébisson ex Ralfs Uncertain placement Astrocosmium Stockmayer, Baccinellula H. Weyland [fossil], Closterimopsis L. M. Yin & Z. P. Li [fossil], Desmidopsis L. M. Yin & Z. P. Li [fossil], Didymidium Reinsch, Paleospiralis Edhorn [fossil], Phycastrum Kützing ex Kützing, Phycoleda Itzigsohn, Polysolenia Ehrenberg ex Kützing, Schizospora Reinsch, Spirogyrites V. B. Shukla [fossil], Spirotaenia Brébisson ex Ralfs, Stenixys T. M. Harris [fossil] See text for authorities of orders and families. http://dx.doi.org/10.4490/algae.2013.28.1.001 2 Guiry Taxonomy and Nomenclature of the Conjugatophyceae OBSERVATIONS fective because of its danger to the unwary. A major mine is apparent in a Code-defined limitation of the principle The “type method” of priority in Article 13.1 by which a “later starting-point” is set as Jan 1, 1848 for the “Desmidiaceae s.l.” (sensu lato; A cornerstone of nomenclature and taxonomy is a sim- meaning in the broad sense), designating Ralfs’s British ple (but frequently ignored or misconstrued) enabling Desmidieae (Ralfs 1848, the date of publication of which principle, the “type method.” Thus every name has a type is artificially designated as Jan 1) as the staring point for and the purpose of this type is, as clearly set out for al- valid publication of desmid names. It should be stressed gae by Silva (1952, p. 241 et seq.), is to provide stability, here that this later starting-point applies to all desmids, essential for effective communication, the raison d’être both saccoderm (the family Mesotaeniaceae of the Zyg- of taxonomy. The International Code of Nomenclature for nematales) and placoderm (all families of the Desmidi- Algae, Fungi and Plants (“Melbourne Code”; McNeill et ales). The application of the Code-defined later starting al. 2012, hereafter referred to as the “Code”), formerly the point to the desmids renders all pre-starting-point names International Code for Botanical Nomenclature, provides nomenclaturally invalid, and these are sporadically re- rules, agreed by the International Botanical Congresses ferred to as “devalidated” names. Unfortunately, it is not (see Nicolson 1991 for a history of the various botanical