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  • Ancestral line of algae leading to higher land plants
  • Three major groups
    • Charales: macroscopic, complex freshwater algae
    • Coleochaetales: flat, disc-like, epiphytic thalli 
    • Zygnematales: filamentous forms and desmids
  • Early divergent forms include the flagellate Mesostigma (possess organic scales, often classified in the Prasinophyceae), the sarcinoid Chlorokybus (several round cells in a common miclage, rare), and the filamentous Klebsormidium

  • left column: Mesostigma (lower) and scales on cell surface; middle column: Chlorokybus; right column: Klebsormidium (four left and lower right photograph courtesy of Charles F. Delwiche, University of Maryland; more information on Charophycean algae at
  • Named after the genus Zygnema
  • Abundant in various freshwaters (ponds, lakes, slow streams)
  • Appearance as filaments and the ornamented desmids
  • Filaments often form slimy patches on the surface, buoyancy provided by oxygen bubbles from photosynthesis captured in mucilage; or attached mats
  • Filamentous species Zygnema and Mougeotia can change their plastid orientation in response to light intensity

  • The filamentous Zygnematales alga Spirogyra

    The orientation of chloroplasts in the genus Mougeotia is changed according to the light regime; low light as in the upper filament, high light as in the lower filament; Right: filamentous Zygnematales can form slimy scum on the surface of eutrophied freshwaters

    The genus Zygnema possesses star-shaped plastids that can be contracted upon high light intensities (compare upper and middle filament in the right picture)
  • Desmids occur in pristine, acidic lakes with low nutrient concentration; they have high phosphorus storage capacities; desmids possess a pore-containing, two-part cell wall separated by a narrow isthmus („placoderm“ desmids)
  • Extensive mucilage is excreted through the cell wall by flask-shaped pores

  • Mucilage prisms can often be seen from excreted mucilage of adjacent pores
  • Cell motility in desmids is due to mucilage excretion; a „slime trail“ can be visualized under the microscope by ink preparations; swelling of the mucilage by water pushes cells forward
  • Asexual reproduction by cell division, typically during the dark period
  • Mitosis is open and centrioles are absent
  • Chloroplast divides by contriction and vacuole forms to separate daughter chloroplasts; plastid division is completed after daughter cells separate
  • Nucleus moves aside the isthmus to give way to material transport to build a new semicell; movement probably by microtubuli arrangement
  • New semicell is identical mirror-image of older semicell
  • Semicells in desmids are of different age!
  • Phragmoplast: desmids lack a phragmoplast; the filamentous forms possess a phragmoplast but not plasmadesmata such as the higher charophytes
  • Sexual reproduction does not involve flagellated gametes
  • Scalariform conjugation is the fusion of nonflagellate gametic thallus cells by lateral plasma connections (conjugation tubes); both gametes might move into the conjugation tube to form a zygote „between“ the filaments (Mougeotia), or only one cell moves through the conjugation tube towards the other cell (Spirogyra)

  • Conjugation stages in Spirogyra; only one protoplast moves into the opposite filament, the zygotes develop in one filament
  • Desmids form their conjugation tube in the isthmus region; cells aggregate by pheromon attraction
  • Zygotes are thick-walled, orange-brown, and diploid; meiosis occurs upon germination
  • Desmid cells originating from zygotes (gones) do not resemble vegetative cells yet
  • Characteristic genus: Coleochaete (gr. Koelos = sheath, chaite = hair)
  • Sheated hairs: extensions of cell wall enclose plasma, can reach 100 times the length of the cell; base of the hair is thickened; sheated hairs are unique to this group
  • Seta cells produce hairs; only 3-5% of thallus cells in Coleochaete; possess C-shaped plastid and rotate

  • See video stream of rotating seta cells in the thallus here (405 kB)
    See video stream of rotating single seta cell here (544 kB)
  • Thallus is pseudoparenchymatous with marginal meristem
  • Asexual reproduction by biflagellate zoospores with organic scales but without eye-spots
  • Sexual reproduction by oogamy; sperms are naked and colorless; egg cells produce trichgyne for fertilization
  • Zygotes are smooth-walled and not released; a layer of vegetative cells growth around and nurishes the zygote
  • Germination: multiple mitotic, flagellated meiospores, which settle for further growth



Charales – the Stoneworts
  • Characteristic genus: Chara
  • Occurrence as extensives meadows in lakes and streams with low phosphate concentrations
  • Calcification colores some species whitish
  • Branched filaments differentiated in apex, nodes, basal region
  • Single apical mestematic cell responsible for length growth; the immediate derviative of apical cell division divides transversely; the upper of these two cells forms a node for branches, the lower one forms a long (up to 15 cm) internodal cell without further division
  • Internodal cells can posses up to 1000 nuclei; cytoplasmic streaming for mixing and long-distance transport within the large cells
  • Cell plate between nodal and internodal cells with large pores from secondary plasmadesmata
  • Plant-like phragmoplast is present during cell division
  • Asexual reproduction by bulbils = white spherical or star-shaped structure on rhizoids; dispersial and perennation
  • Sexual reproduction by oogamy with two types of gametangia
  • Gametangia possess protective, nonreproductive layers of cells for protection and originate from node cells
  • Antheridia produce biflagellated spermatozoids; mature antheridia are bright orange due to carotene in an outer layer of cells (shield cells); primary capitulum cells (8) produce long strings of small cells, each of them producing one spermatozoid
  • Ooginia produce a single egg cell, enclosed by tube cells (laterally) and 1-2 crown cells (top)
  • Zygote with thick, dark-brown wall; tube cells calcify; zygote released upon decay of mother thallus together with calcified tube cell shield
  • Germination: meiosis, but probably only one cell surviving; growth of a colorless protonema, which attaches to substrate and produces colored cells at is apical end

  • Left: thin section through a Chara antheridium, note 
    the layer of non-reproductive cells around the inner reproductive cells; right: spermatozoids in long strings 
    of spermatozoid-producing cells from an antheridium

Different desmids

Cell division sequence in the desmid Micrasterias

Conjugation in Mougeotia: both cell protoplasts move into the conjugation tube, the zygotes develop "between" the two filaments

Zygotes of the desmid Micrasterias


Upper: Chara sp.;  middle: Nitella sp. (courtesy of Charles F. Delwiche, University of Maryland); lower: thin section through the apical meristem cell of Chara

Oogonia (elongated) and antheridia (round) can occur at the same node (above) or at different nodes (left), depending on the Chara species

Mature antheridia appear orange on the Chara branches, the zygotes appear brown