The origin and early diversification of the Ulvophyceae likely took place in the late
Neoproterozoic,[8][9] though may have taken place earlier, in the Mesoproterozoic.[10] Although most contemporary ulvophytes are marine macroalgae (
seaweeds),
ancestral ulvophytes may have been freshwater, unicellular green algae. Molecular phylogenetic evidence suggests that macroscopic growth was achieved independently in the various major lineages of Ulvophyceae (
Ulvales-
Ulotrichales,
Trentepohliales,
Cladophorales,
Bryopsidales and
Dasycladales).[9] Fossils are rare but there are some good candidates in a mid-Ordovician
lagerstatten.[1]
Current hypothesis on relationships among the main clades of Ulvophyceae[11][12] are shown below.
^Stewart KD, Mattox KR (April 1978). "Structural evolution in the flagellated cells of green algae and land plants". Bio Systems. 10 (1–2): 145–152.
doi:
10.1016/0303-2647(78)90036-9.
PMID656563.
^Verbruggen H, Ashworth M, LoDuca ST, Vlaeminck C, Cocquyt E, Sauvage T, et al. (March 2009). "A multi-locus time-calibrated phylogeny of the siphonous green algae". Molecular Phylogenetics and Evolution. 50 (3): 642–653.
doi:
10.1016/j.ympev.2008.12.018.
PMID19141323.
^Škaloud P, Kalina T, Nemjová K, De Clerck O, Leliaert F (February 2013). "Morphology and Phylogenetic Position of the Freshwater Green Microalgae Chlorochytrium (Chlorophyceae) and Scotinosphaera (Scotinosphaerales, ord. nov., Ulvophyceae)". Journal of Phycology. 49 (1): 115–129.
doi:
10.1111/jpy.12021.
PMID27008394.
S2CID7359581.