This article was downloaded by: [British Phycological Society BPS ] On: 15 August 2011, At: 12:20 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK British Phycological Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejp19 The taxonomy of the Chlorophyta. II F.E. Round a a Department of Botany, University of Bristol Available online: 02 Aug 2011 To cite this article: F.E. Round (1971): The taxonomy of the Chlorophyta. II, British Phycological Journal, 6:2, 235-264 To link to this article: http://dx.doi.org/10.1080/00071617100650261 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and- conditions This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan, sub- licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Br. phyeol. J. (1971) 6 (2) 235-264 October 31, 1971 THE TAXONOMY OF THE CHLOROPHYTA. II By F. E. ROUND Department of Botany, University of Bristol The taxonomy of all the algal groups possessing both chlorophyll a and b is discussed for the levels above that of the family. Much of the discussion is related to previously conceived taxa but some new combinations are proposed. The subdivision of 'green' algae into Euglenophyta, Prasinophyta, Charophyta and Chlorophyta is discussed in the light of recent publications. The problem of further subdivision in the Chlorophyta is reviewed and the need stressed for more extensive electron microscopical and biochemical evidence. Until such data are available the author favours maintaining a large number of orders but also the rejection of those based on single characters. 'The appearance of new systems of classification does not at all signify the destruction of everything old for much from the old systems enters into the new ones as component elements.' Armon Takhtajan, 1968 'We are seeking a "natural" classification. The test for such a "natural" classification is its internal consistency: the accuracy by which one can predict unknown features of an organism when one knows its assigned taxonomic position.' Ralph A. Lewin, 1968 There have been eight years of intense work in phycology since I attempted a tentative discussion of some problems in the taxonomy of the green algae (Round, 1963). This work yields an even clearer picture of the group and I am encouraged to attempt a re-evaluation since many phycologists have commented to me on the 1963 paper; some have found it useful as a basis for teaching the group (which is encouraging since, as Koch (1960) remarks, one of the important applications of taxonomy is its usefulness to students) and, as I hoped, others have applied new techniques to test the hypotheses. Table I, taken directly from the i963 publica- tion, summarises the groupings which then appeared to me to be emerging. It was in many ways a cautious approach and evidence has now accumulated which, although not altering the basic entities, warrants the upgrading of some Downloaded by [British Phycological Society BPS ] at 12:20 15 August 2011 to a higher status. The points listed in 1963 are still worthy of consideration: (1) How many phyla (divisions) are involved ? (2) How many classes should be re- cognised ? (3) What is the best subdivision of these classes into orders ? (4) What genera belong in each order ? This latter question cannot be dealt with in detail here; only certain critical genera can be discussed. The size of the problem is obvious when one considers that Bourrelty (1966) lists 565 freshwater genera alone. As in 1963, many of the schemes have been proposed at various times by other phycologists and I am merely attempting to draw these together and hope that this will stimulate and point the way to further work to test the hypotheses. 235 TABLE 1. The scheme of classification of the 'green' algae proposed in Round (•963). EUCARYOTA--CONTOPHORA Phylum Chlorophyta (Chromophyta) I I I I Subphylum Euglenophytina Chloroph 'tina Charop~ytina Prasinophytina I I Class Euglenophyceae Charophyceae Prasinophyceae Order Euglenales Charales Prasinovolvocales Prasinococcales Prasinodendrales I I I I Class Conjugatophyceae Oedogoniophyceae Bryopsidophyceae Loxophyceae Chlorophyceae Order Mesotaeniales Oedogoniales Zygnematales Gonatozygales Desrnidiales 0 7, I I Hemisiphoniidae Cystosiphoniidae Eusiphoniidae I Downloaded by [British Phycological Society BPS ] at 12:20 15 August 2011 I I Cladophorales Chlorochytriales Derbsiales Sphaeropleales Siphonocladales Codiales Dasycladales Caulerpales Dichotomosiphonales I I Volvocales Chaetophorales Tetrasporales or Chlorococcales f Ulvellales ] Chlorosphaerales Chaetophorales | Ulotrichales -~ Trentepohliates Ulvales Coleochaetales I Prasiolales ~Pleurococcales ] Microsporales Taxonomy of Chlorophyta. II 237 PHYLA I now believe my caution over the first question was unnecessary and we can return to the much earlier concept of several phyla rather than subphyla. It is interesting that Banks (1968) in a stimulating paper on the early history of land plants also uses sub-divisions (sub-phyla) for groups which other workers would regard as divisions (e.g. Rhyniophyta, Lycophyta, Sphenophyta, etc.; see also Cronquist, Takhtajan and Zimmermann, 1966) and maintains a single division Tracheophyta, for all vascular plants above the bryophyte level. Surely a division should be based on more than the possession of vascular strands! This is, I be- lieve, directly comparable to maintaining the phylum Chlorophyta for all green algae. It is difficult to find a characteristic other than the possession of both chlorophyll a and b to embrace this series of algae and, though Christensen (1962) used this to segregate his Chlorophyta from the Chromophyta, it is surely neither a sufficient criterion to hold such a varied assemblage together as a single phylum nor sufficient to embrace all green plants which logically it should (see also Bold, 1956; Fott, 1965). In fact, Bold (1957) did bring all the divisions of plants containing chlorophyll a into a sub-kingdom, Chlorota. Three other characters of the chloroplast, namely, absence of girdle bands (groups of thyla- koids passing around the ends of the main series of longitudinally running bands), tight apposition of the thylakoids, and evaginations or invaginations of the thylakoids, are common to the 'chlorophyte' and tend to be absent from most or all 'chromophyte' algae (Gibbs, 1970); however, on similar criteria the 'chromophyte' series itself does not form an entity. Indeed, although the 'chromophyte' series is a valuable concept in that it distinguishes the 'non-green' algae (including, however, the Xanthophyceae) from others and has stimulated much work, the algal groups contained within it no more constitute a single phylum than those in Christensen's Chlorophyta. Equally it is unsatisfactory to group all algae together in the same division, Phycophyta, as Koch (1960) pro- posed and as used by M~igdefrau in Strasburger (1967). Whittaker (1969) uses the term Euchlorophyta for a sub-kingdom of the kingdom Plantales; the Chlorophycophyta forms a branch of the Euchlorophyta and contains the Chlorophyta and Charophyta. Whilst this may be a useful concept it is exceed- ingly confusing to use -phyta for three different classificatory levels. The literature on algae is virtually devoid of philosophical discussion on the concept of phyla and indeed of most taxonomic entities. The concept of a phy- lum is derived from a consideration of the major vegetative and reproductive characteristics of a number of genera all showing a similar manifestation of these Downloaded by [British Phycological Society BPS ] at 12:20 15 August 2011 characteristics. Without denying that phyla may be derived from one another at some stage in their evolutionary development they appear to be lines with long independent fossil histories. The vegetative and reproductive basis is most clearly recognised in the plants with more complex anatomy from the Bryophyta upwards and in most of the more complex animal phyla. Thus in at least 99 ~ of cases anyone encountering a new leafy or thalloid non-vascular plant with archegonia, antheridia or sporogonia immediately assigns it to the correct phy- lum or one of two phyla if one follows Bold (1956).* Clearly a phylum such as * The fact that a very small number of genera cannot be classified easily and are the subject of controversy, e.g. the genus Psilotum, does not in any way detract since these genera often require further detailed studies. 238 F.E. ROUND Bryophyta has some characters common to other phyla (and, indeed, phyla have certain features, particularly nuclear characteristics, in common), but super- imposed on these are certain well defined biochemical, morphological and re- productive characters which