Charophyceae - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/charophyceae/125700
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Article by: Chapman, Russell L. Department of Botany, Louisiana State University, Baton Rouge, Louisiana. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097-8542.125700 (http://dx.doi.org/10.1036/1097-8542.125700)
Content
Morphology Life history Bibliography Taxonomy and phylogeny Fossils Additional Readings
A group of branched, filamentous green algae, commonly known as the stoneworts, brittleworts, or muskgrasses, that occur mostly in fresh- or brackish-water habitats. They are important as significant components of the aquatic flora in some locales, providing food for waterfowl and protection for fish and other aquatic fauna; as excellent model systems for cell biological research; and as a unique group of green algae thought to be more closely related to the land plants.
Morphology
Charophytes are multicellular, branched, macroscopic filaments from a few inches to several feet in length. Colorless rhizoidal filaments anchor the plants to lake bottoms and other substrates. The main filaments are organized into short nodes forming whorls of branches, and much longer (up to 6 in. or 15 cm) internodal cells. The general morphology varies with environmental conditions such as depth of the water, light levels, and amount of wave action. Reproductive structures occur at the nodes and consist of egg cell–containing structures, the nucules, and sperm cell–containing structures called globules. The biflagellated sperm cells are produced in antheridial filaments within the globules. In many charophytes, calicium carbonate (lime) is secreted on the cell walls, hence the name stoneworts or brittleworts. In some charophytes, the simple structure of nodal and intermodal cells is complicated by corticating elements that cover the cells of the main axis.
Taxonomy and phylogeny
Based on the morphology of the vegetative filaments and the reproductive structures, six extant genera are recognized: Chara, Nitella, Tolypella, Nitellopsis, Lamprothamnium, and Lychnothamnus. At the species level, there is significant disagreement with regard to the importance and interpretation of morphological features, life cycles, and biogeography, especially for Chara. Hence, there is no agreement on how many valid species exist, but the maximum number of living species is probably fewer than 100. Among the special features that support the suggestion that the charophytes are closely related to the land plants are the morphologically complicated reproductive structures, the ultrastructure of the sperm cells, and the type of cell division. Some of these features have led some scientists to include other genera of green algae in this group known as the Charophyceae. Deoxyribonucleic acid (DNA) sequencing indicates that the charophytes are a distinct natural group that should be recognized at some taxonomic level (for example, as an order, Charales, or as a class, Charophyceae).
Life history
1 of 3 11/17/2015 7:49 AM Charophyceae - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/charophyceae/125700 The charophytes are haploid organisms. The fusion of the sperm and egg cell produces a diploid resistant zygote which, after dormancy, undergoes meiosis to produce a new haploid generation. Thus, there is no alternation of generations. Asexual zoospores are not produced, but plants can reproduce vegetatively as the rhizoidal filaments spread and develop new plants. See also: Plant reproduction (/content/plant-reproduction/581300)
Fossils
Because the fertilized egg cells produce resistant, calcified zygotes, fossils (known as gyrogonites) provide a record of these organisms extending back to the Devonian Period (approximately 360–408 million years ago). Many genera that once existed are now extinct. See also: Algae (/content/algae/022000); Chlorophycota (/content/chlorophycota/132150); Paleobotany (/content/paleobotany/483200)
Russell L. Chapman
Bibliography
H. C. Bold and M. J. Wynne, Introduction to the Algae: Structure and Reproduction, 2d ed., 1985
A. Sze, A Biology of the Algae, 3d ed., 1997
Additional Readings
R. Bock and V. Knoop (eds.), Genomics of Chloroplasts and Mitochondria, Springer, New York, 2012
S. Kato et al., Morphology and molecular phylogeny of Chara altaica (Charales, Charophyceae), a monoecious species of the section Desvauxia, Cytologia, 75(2):211–220, 2010
M. B. J. Moniz, F. Rindi, and M. D. Guiry, Phylogeny and taxonomy of Prasiolales (Trebouxiophyceae, Chlorophyta) from Tasmania, including Rosenvingiella tasmanica sp. nov, Phycologia, 51(1):86–97, 2012 DOI: 10.2216/10-103.1 (http://dx.doi.org/10.2216/10-103.1)
O. P. Sharma, Algae, Tata McGraw-Hill Education, New Delhi, India, 2011
E. L. Taylor, T. N. Taylor, and M. Krings, Paleobotany: The Biology and Evolution of Fossil Plants, 2d ed., Academic Press, New York, 2009
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