Charophytes + Zygnematophytes

Sister groups to land plants

The page includes the clade of green algae that are a sister group to the land plants (embryophytes). The clade that include these green algae plus land plants has been called the Phragmoplastophyta, because they create a phragmoplast during cell division: a scaffold-like structure that forms during late cytokinesis and aids in cell plate construction and formation of a new cell wall. This algae in this clade include the Charophyceae, Coleochaetophyceae, and Zygnematophyceae (Lecointre & Guyader 2006)

Ecology & Form

  • These are the most closely-related algae to land plants

  • They are mostly freshwater or terrestrial algae

  • They consist of unicellular, colonial, filamentous or parenchymatous forms

  • Similar to land plants, they form a phragmoplast: a scaffold-like structure that forms during late cytokinesis and aids in cell plate construction and formation of a new cell wall

  • They exhibit branched apical growth like ancestral land plants

Life cycle

Different than land plants, these algae exhibit a haplontic life cycle (=no multicellular sporophyte generation)

  • The algae is haploid, and forms gametes which are created and fuse through fertilization

  • The resultant zygote does not go through mitosis, but instead goes through meiosis to create spores

  • These spores are released into water to germinate into new gametophytes

Above: Close-up of spiraling chloroplast of Spirogyra

Above: Conjugation (reproduction) of Spirogyra

Diversity

Zygnematophyceae

  • This group has several thousand different species in two families

  • Unbranched, filamentous; cell division with a phragmoplast

  • Sometimes called the Conjugatales, since they perform "conjugation" during reproduction

  • Spirogyra, called the water-silk, and Zygnema are common as freshwater pond "scum"

  • Evidence indicates that these are the most-closely-related algae to the land plants (Cheng et al. 2019)

Above: Zygnema

Above: Spirogyra, the water-silk

The below algae were originally thought to be the closest relatives to land plants, due to their parenchymatous and apical growth

Coleochaetales (Coleochaetales)

    • Parenchymatous algae, like land plants

    • Coleochaete is a flat, disk-like algae that lives as an epiphyte on basal portions of marsh plants

    • Coleochaete has sterile cells that surround the zygotes after fertilization, but unlike land plants, it has a haplontic lifecycle with meiosis taking place directly in the zygote (and not in diploid cells resulting from mitosis of the zygote)

Charophyceae (Charales)

    • Parenchymatous, with apical branching

    • Chara, also called a stonewort, is found in fresh water, particularly in limestone areas

Above: Coleochaete

Above: the stonewort, Chara

Additional Resources