Phycokey - Coleochaete

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Name derivation:
Sheathed bristle koleos (Gr.) = sheath, chaete (gr.) = bristle
Classification:
Coleochaete Brébisson 1844; 15 of 31 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013). Order Coleochaetales; Family Coleochaetaceae Synonym: Phyllactidium Kutzing 1843
Morphology:
Flat mat one cell thick, generally round, with short upward branches bearing gametangia -- spermatocytes toward the mat perimeter, oocytes toward the center of the mat. Dorsal setae develop lengths often >100 times the cell diameter, surrounded by a sheath (Rockwell 2015). Adjacent cells communicate via plasmdesmata Ultrastructural, biochemical and molecular evidence demonstrates close relationship to ancestry of embryophytes (Guiry and Guiry 2013).
Morphological Disorientation:
Experimental illumination from the ventral side of the flat dorsiventral thallus caused loss of dorsal hairs and loss of dorsiventral morphology. Directional growth in Sphagnum moss and liverworts was also reversed. In all cases gravity had less control on orientation (Cardona-Correa, Ecker and Graham 2015).
Similar genera:
The outer row of cells of Pediastrum duplex have similar two-horned cells .
Sexual reproduction
Coleochaete spp. are oogamous, considered to be more advanced than isogamy and anisogamy. Species are dioicous (two unisexual gametophytes, one female and the other male. Antheridia develop along the periphery of male gametophytes, each one producing a single sperm (flagellated microgamete) – perhaps unique among chlorophyceae. Oogonia develop near the periphery of female gametophytes. Zygotes are retained on the female mat (gametophyte), similar to their retention on other ‘embryophytes’ such as Chara, Nitella, and land plants, and are protected by a layer of somatic cells that grow around them. Typical of all photosynthetic protists except diatoms, the zygote (2N) undergoes meiosis prior to mitosis, thus the life cycle is called haplontic (1N nuclei). Several mitotic divisions of the zygote result in 8 to 32 haploid zoospores that are eventually released and disperse. The haploid zoospores are either female or male, thus the gametophytes (mats) are unisexual, the females producing oogonia and the males producing antheridia from spermatogonia.
Asexual reproduction
Vegetative cells from vegetative cells in the female gametophyte5 mat can escape from their cellulose walls and form zoospores that disperse, lose their flagella, become attached to a surface and resume mitosis to form a new flat mat (gametophyte). The old cell walls in the parental mat persist as empty ‘skeletons’. Because all the asexual progeny from the female gametophytes contain only the female genes, all new gametophytes are also female. This is in contrast to only 50% of the sexual progeny from germinating zygotes (Haig and Wilczek 2006).
Origin of Land Plants:
Coleochaete develops a placenta that enables material distribution to its gametes, that consists of cells secretory cells similar to the placenta that connectes the sporophyte and gemetophye generations of land plants (Graham et al. 2000).
Habitat:
Freshwater lakes, both planktonic, aufwuchs, and benthic. Grows well attached to the glass of aquaria.

References:
Brébisson, [L.] A. de 1844. Description de deux nouveaux genres d'algues fluviatiles. Annales des Sciences Naturelles, Botanique3: 25-31, 2 pls. Cardona-Correa, C., A. Ecker and L.E. Graham 2015. Direction of illumination controls gametophyte orientation in seedless plants and related algae. Plant Signaling and Behavior: Accepted version posted online. Guiry, M.D. and G.M. Guiry 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 03 May 2013. Graham, L.E., M.E. Cook and J.S. Busse 2000. The origin of plants: Body plan changes contributing to a major evolutionary radiation. Proceedings of the National Academy of Sciences 97(9):4535-4540. Haig, D., and A. Wilczek 2006. Sexual conflict and the alternation of haploid and diploid generations. Philosophical Transactions R, Royal Society of London B Biological Science 361(1466):355-343. Kützing, F.T. 1843. Phycologia generalis oder Anatomie, Physiologie und Systemkunde der Tange... Mit 80 farbig gedruckten Tafeln, gezeichnet und gravirt vom Verfasser. pp. [part 1]: [i]-xxxii, [1]-142, [part 2:] 143-458, 1, err.], pls 1-80. Leipzig: F.A. Brockhaus. Rockwell, T.R. 2015. Seta structure in members of the coleochaetales (streptophyta). Illinois State University Theses and Dissertations Paper 376. online

Name derivation:

Classification:

Coleochaete Brébisson 1844; 15 of 31 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013).

Order Coleochaetales; Family Coleochaetaceae

Synonym: Phyllactidium Kutzing 1843

Morphology:

Morphological Disorientation:

Similar genera:

Sexual reproduction

Zygotes are retained on the female mat (gametophyte), similar to their retention on other ‘embryophytes’ such as Chara, Nitella, and land plants, and are protected by a layer of somatic cells that grow around them.

Typical of all photosynthetic protists except diatoms, the zygote (2N) undergoes meiosis prior to mitosis, thus the life cycle is called haplontic (1N nuclei). Several mitotic divisions of the zygote result in 8 to 32 haploid zoospores that are eventually released and disperse.

The haploid zoospores are either female or male, thus the gametophytes (mats) are unisexual, the females producing oogonia and the males producing antheridia from spermatogonia.

Asexual reproduction

Because all the asexual progeny from the female gametophytes contain only the female genes, all new gametophytes are also female. This is in contrast to only 50% of the sexual progeny from germinating zygotes (Haig and Wilczek 2006).

Origin of Land Plants:

Coleochaete develops a placenta that enables material distribution to its gametes, that consists of cells secretory cells similar to the placenta that connectes the sporophyte and gemetophye generations of land plants (Graham et al. 2000).

Habitat:

References: