Viridiophytes: green plants

Individual genera at the termini of this tree are prasinophyceans, once thought to be a monophyletic group. They are unicelluar, mostly motile, and thought to be the most primitive green “plants”. Different prasinophycean groups appear to have diverged anciently, resulting in the two main lineages of green organisms: the UTC Clade and streptophytes (= Charophyceans + Embryophytes). Those on the branch leading to the UTC Clade are mainly marine flagellates covered in scales. Mesostigma is also a prasinophycean, and thought to be the earliest divergent of the Streptophyte lineage. It is a freshwater form, fitting the hypothesis that the charophycean radiation occurred in such habitats. Lemieux et al. (2000) presented three alternative topologies involving Mesostigma. Although their preferred topology T1 is presented here, their T3 (which places the organism basal to streptophytes rather than to all green organisms) is more consistent with morphology and habitat. Although it is now generally accepted that charophyceans are the closest living relatives of the land plants, molecular analyses have not fully resolved this relationship. Various analyses have suggested charaleans, early-divergent charophyceans (Coleochaete, Klebsormidium) or zygnemataleans as closest to land plants. Here we opt for a conservative approach in which the embryophytes emerge basally to the entire charophycean class, pending further conclusive evidence.

Indigenous or exotic to New Zealand.

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

Kendrick, P.; Crane, P. R. 1997: The origin and early diversification of land plants: a cladistic study. Smithsonia Institution Press, Washington.
Lemieux, C.: Otis, C:, Turmel, M. 2000: Ancestral chloroplast genome in Mesostigma viride reveals an early branch of green plant evolution. Nature, 403, 649–652.
Nakayama, T.; Marin, B.; Kranz, H. D.; Surek, B.; Huss, V.A.R.; Inouye, I.; Melkonian, M. 1988: The basal position of scaly green flagellates among the green algae (Chlorophyta) is revealed by analysis of nuclear-encoded SSU rRNA sequences. Protist 149: 367–380.
Steinkötter, J.; Bhattacharya, D.; Semmelroth, I.; Bibeau, C.; Melkonian, M. 1994: Prasionophytes form independent lineages within the Chlorophyta – evidence from ribosomal RNA sequence comparison. Journal of Phycology 30: 340–345.
Phil Novis Phycologist 
Last updated: 04-Feb-2016