With the Embryophyta nowcladistically placed in the Charophyta, it is a synonym ofStreptophyta.[10][11][12][13] The sister group of the charophytes are theChlorophyta. In some charophyte groups, such as theZygnematophyceae or conjugating green algae,flagella are absent and sexual reproduction does not involve free-swimming flagellate sperm. Flagellate sperm, however, are found instoneworts (Charales) andColeochaetales, orders of parenchymatous charophytes that are the closest relatives of the land plants, where flagellate sperm are also present in all except theconifers andflowering plants.[14] Fossil stoneworts of earlyDevonian age that are similar to those of the present day have been described from theRhynie chert of Scotland.[15] Somewhat different charophytes have also been collected from the Late Devonian (Famennian)Waterloo Farm lagerstätte of South Africa. These include two species each ofOctochara andHexachara, which are the oldest fossils of Charophyte axes bearing in situoogonia.
The name comes from thegenusChara, but the finding that the Embryophyta actually emerged in them hasnot resulted in a much more restricted meaning of the Charophyta, namely to a much smaller side branch. This more restricted group corresponds to theCharophyceae.
TheZygnematophyceae, formerly known as the Conjugatophyceae, generally possess two fairly elaboratechloroplasts in each cell, rather than many discoid ones. They reproduceasexually by the development of a septum between the two cell-halves or semi-cells (in unicellular forms, each daughter-cell develops the other semi-cell afresh) and sexually by conjugation, or the fusion of the entire cell-contents of the two conjugating cells. The saccoderm desmids and the placoderm or true desmids, unicellular or filamentous members of the Zygnematophyceae, are dominant in non-calcareous, acid waters of oligotrophic or primitivelakes (e.g. Wastwater), or in lochans, tarns and bogs, as in the West of Scotland, Eire, parts of Wales and of the Lake District.[16]
Klebsormidium, the type of theKlebsormidiophyceae, is a simple filamentous form with circular, plate-like chloroplasts, reproducing by fragmentation, by dorsiventral,biciliate swarmers and, according to Wille, a twentieth-century algologist, byaplanospores.[17] Sexual reproduction is simple andisogamous (the male and female gametes are outwardly indistinguishable).[17]
TheCharales (Charophyceae), or stoneworts, are freshwater andbrackish algae with slender green or grey stems; the grey colour of many species results from the deposition of lime on the walls, masking the green colour of the chlorophyll. The main stems are slender and branch occasionally. Lateralbranchlets occur inwhorls at regular intervals up the stem, they are attached by rhizoids to the substrate.[18] The reproductive organs consist ofantheridia andoogonia, though the structures of these organs differ considerably from the corresponding organs in other algae. As a result of fertilization, aprotonema is formed, from which the sexually reproducing algae develops.[citation needed]
A new terrestrial genus found in sandy soil in theCzech Republic,Streptofilum, may belong in its own class due its unique phylogenetic position. Acell wall is absent, instead thecell membrane consists of many layers of specific scales. It is a short, filamentous and unbranched algae surrounded by a mucilaginous sheath, which often disintegrates to diads and unicells.[19]
The cells in Charophyta algae are allhaploid, except during sexual reproduction, where a diploid unicellular zygote is produced. The zygote becomes four new haploid cells through meiosis, which will develop into new algae. In multicellular forms these haploid cells will grow into agametophyte. In embryophytes (land plants) the zygote will instead give rise to a multicellularsporophyte.[20][21]
Except from land plants, retention of the zygote is only known from some species in one group of green algae; thecoleochaetes. In these species the zygote is corticated by a layer of sterile gametophytic cells. Another similarity is the presence ofsporopollenin in the inner wall of the zygote. In at least one species, it receives nourishment from the gametophyte through placental transfer cells.[22]
Charophyta are complex green algae that form a sister group to theChlorophyta and within which theEmbryophyta emerged. Thechlorophyte and charophyte green algae and the embryophytes or land plants form a clade called the green plants orViridiplantae, that is united among other things by the absence ofphycobilins, the presence ofchlorophyll a andchlorophyll b, cellulose in the cell wall and the use ofstarch, stored in the plastids, as a storage polysaccharide. The charophytes and embryophytes share several traits that distinguish them from the chlorophytes, such as the presence of certain enzymes (class Ialdolase, Cu/Znsuperoxide dismutase,glycolate oxidase, flagellarperoxidase), lateral flagella (when present), and, in many species, the use ofphragmoplasts inmitosis.[23] Thus Charophyta and Embryophyta together form the cladeStreptophyta, excluding the Chlorophyta.[citation needed]
Charophytes such asPalaeonitella cranii and possibly the yet unassignedParka decipiens[24] are present in the fossil record of theDevonian.[15]Palaeonitella differed little from some present-day stoneworts.[citation needed]
There is an emerging consensus on green algal relationships, mainly based on molecular data.[23][25][26][27][10][2][6][28][29][30][31][32][19][33] The Mesostigmatophyceae (includingSpirotaenia, and Chlorokybophyceae) are at the base of charophytes (streptophytes). The cladograms below show consensus phylogenetic relationships based on plastid genomes[34] and a new proposal for a third phylum of green plants based on analysis of nuclear genomes.[35]
Relationships among major green algal lineages based on a recent nuclear phylogenomic study[35]
Mesostigmatophyceae s.l. in the cladograms corresponds to a clade of a narrower circumscription, Mesostigmatophyceae s.s., and a separate class Chlorokybophyceae, as used byAlgaeBase.[1]
The Mesostigmatophyceae[which?] are not filamentous, but the other basal charophytes (streptophytes) are.[36][19][30]
^Treatise on invertebrate paleontology. Part B. Protoctista 1. Volume1: Charophyta.[1]
^abCook, Martha E.; Graham, Linda E. (2017). "Chlorokybophyceae, Klebsormidiophyceae, Coleochaetophyceae". In Archibald, John M.; Simpson, Alastair G. B.; Slamovits, Claudio H. (eds.).Handbook of the Protists. Springer International Publishing. pp. 185–204.doi:10.1007/978-3-319-28149-0_36.ISBN9783319281476.
^abKelman, R.; Feist, M.; Trewin, N.H.; Hass, H. (2003). "Charophyte algae from the Rhynie chert".Transactions of the Royal Society of Edinburgh: Earth Sciences.94 (4):445–455.doi:10.1017/s0263593300000808.S2CID128869547.
^West, G.S; Fritsch, F.E. (1927).A Treatise of the British Freshwater Algae. Cambridge: Cambridge University Press.
^abFritsch, F.E. (1935).The Structure and Reproduction of the Algae, vol I. Cambridge University Press. pp. 205–206.
^Bryant 2007, J. The Stoneworts (Chlorophyta, Charales) in Guiry, M.D., John, D.M., Rindi, F. and McCarthy, T.K (Ed)New Survey of Clare Island Volume 6: The Freshwater and Terrestrial Algae. Royal Irish Academy.ISBN9781904890317
^Hemsley, A.R. (1989). "The ultrastructure of the spores of the Devonian plantParka decipiens".Annals of Botany.64 (3):359–367.doi:10.1093/oxfordjournals.aob.a087852.
^Marin, Birger (2012). "Nested in the Chlorellales or Independent Class? Phylogeny and Classification of the Pedinophyceae (Viridiplantae) Revealed by Molecular Phylogenetic Analyses of Complete Nuclear and Plastid-encoded rRNA Operons".Protist.163 (5):778–805.doi:10.1016/j.protis.2011.11.004.PMID22192529.
Data related toCharophyta at Wikispecies
