Phylogeny
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Zygnematales

Viridiophytes: green plants -> Charophyceae

The placement of the Zygnematales among the charophyceans became apparent mainly through molecular analysis, prior authors generally assuming they shared a recent common ancestor with chlorophycean algae. Subsequently, however, land-plant-like peroxisomes have been found in zygnemataleans (as are also found in Klebsormidium), and one molecular analysis places them as sister to the bryophytes. They are difficult to classify by traditional means, since flagellate cells are wholly absent from zygnematalean life cycles; flagellate cells of other charophycean groups display strong similarities with the motile sperm cells of those embryophytes that still retain them. Sexual reproduction occurs through conjugation and fusion of amoeboid gametes; hence the alternative name of Conjugales. Within the Zygnematales, the traditional classification based on thallus shape (filamentous versus unicellular) has been overturned, molecular analyses having shown that plastid shape is a more accurate phylogenetic criterion among the filaments and the saccoderm desmids. The concept of the Desmidiales (placoderm desmids), however, has largely survived this rearrangement. Recent findings that place the saccoderm desmid Spirotaenia rather controversially are currently omitted here.

Indigenous or exotic to New Zealand.

NZ Flora Web Site Link to the Ngā Tipu o Aotearoa Database

 
References
Gontcharov, A.A., Melkonian, M. (2004) Unusual position of the genus Spirotaenia (Zygnematophyceae) among streptophytes revealed by SSU rDNA and rbcL sequence comparisons. Phycologia, 43, 105–113.
McCourt, R.M., Karol, K.G., Bell, J., Helm-Bychowski, K.M., Grajewska, A., Wojciechowski, M.F., Hoshaw, R.W. (2000) Phylogeny of the conjugating green algae (Zygnemophyceae) based on rbcL sequences. Journal of Phycology, 36, 747–758.
Roles
Phil Novis PhycologistPhycologist
Last updated: 05-Mar-2013