The origin and early diversification of the Ulvophyceae likely took place in the late
Neoproterozoic.[8][9] 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[10][11] are shown below.
^Stewart KD, Mattox KR (1978). "Structural evolution in the flagellated cells of green algae and land plants". BioSystems. 10 (1–2): 145–152.
doi:
10.1016/0303-2647(78)90036-9.
PMID656563.
^Škaloud, Pavel; Kalina, Tomáš; Nemjová, Katarína; De Clerck, Olivier; Leliaert, Frederik (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.
ISSN0022-3646.
PMID27008394.
S2CID7359581.