The Cryogenian period (720–635 million years ago) is linked to the origin of multicellularity in Archaeplastida, including the first land plants. A time-calibrated phylogeny of early archaeplastid evolution was inferred using a revised molecular dataset and reassessment of the fossil record. Phylogenetic analysis resolved deep archaeplastid relationships, identifying two clades of Viridiplantae and placing Bryopsidales as sister to the Chlorophyceae. Molecular clock analysis inferred the origin of Archaeplastida in the late Paleoproterozoic to early Mesoproterozoic (1712–1387 Ma). Ancestral state reconstruction of cytomorphological traits revealed that many independent origins of multicellularity span the Cryogenian, consistent with the Cryogenian multicellularity hypothesis. Multicellular rhodophytes emerged 902–655 Ma, while crown-Anydrophyta (Zygnematophyceae and Embryophyta) originated 796–671 Ma, broadly compatible with the Cryogenian plant terrestrialization hypothesis. The timetree of Archaeplastida aligns with the Cryogenian, supporting hypotheses that propose a role of Snowball Earth in plant evolution. The study resolves the evolutionary timeline of Archaeplastida, showing that the origin of multicellularity and terrestrialization occurred during the Cryogenian, consistent with the Snowball Earth hypothesis. The results suggest that Cryogenian glaciations facilitated the evolution of multicellularity in plants and provided a unique ecological environment for the development of land plants. The study also highlights the importance of environmental factors in the evolution of multicellularity and plant terrestrialization. The findings support the idea that Cryogenian conditions played a key role in the transition from aquatic to terrestrial life for early plants. The study provides a detailed timeline of archaeplastid evolution, showing that multicellularity and land plant evolution occurred during the Cryogenian, consistent with the Snowball Earth hypothesis. The results are compatible with the hypothesis that ancient glaciations facilitated the origin of multicellularity in plants. The study also shows that the Cryogenian period was a critical time for the evolution of multicellularity and plant terrestrialization, with the emergence of multicellular algae and the first land plants occurring during this period. The findings suggest that the Cryogenian was a pivotal time in the history of life on Earth, with the development of multicellularity and land plants being closely linked to the Snowball Earth events. The study provides a comprehensive understanding of the evolutionary history of Archaeplastida, showing that the Cryogenian was a key period in the development of multicellularity and plant terrestrialization. The results support the hypothesis that the Cryogenian period was a critical time for the evolution of multicellularity and the transitionThe Cryogenian period (720–635 million years ago) is linked to the origin of multicellularity in Archaeplastida, including the first land plants. A time-calibrated phylogeny of early archaeplastid evolution was inferred using a revised molecular dataset and reassessment of the fossil record. Phylogenetic analysis resolved deep archaeplastid relationships, identifying two clades of Viridiplantae and placing Bryopsidales as sister to the Chlorophyceae. Molecular clock analysis inferred the origin of Archaeplastida in the late Paleoproterozoic to early Mesoproterozoic (1712–1387 Ma). Ancestral state reconstruction of cytomorphological traits revealed that many independent origins of multicellularity span the Cryogenian, consistent with the Cryogenian multicellularity hypothesis. Multicellular rhodophytes emerged 902–655 Ma, while crown-Anydrophyta (Zygnematophyceae and Embryophyta) originated 796–671 Ma, broadly compatible with the Cryogenian plant terrestrialization hypothesis. The timetree of Archaeplastida aligns with the Cryogenian, supporting hypotheses that propose a role of Snowball Earth in plant evolution. The study resolves the evolutionary timeline of Archaeplastida, showing that the origin of multicellularity and terrestrialization occurred during the Cryogenian, consistent with the Snowball Earth hypothesis. The results suggest that Cryogenian glaciations facilitated the evolution of multicellularity in plants and provided a unique ecological environment for the development of land plants. The study also highlights the importance of environmental factors in the evolution of multicellularity and plant terrestrialization. The findings support the idea that Cryogenian conditions played a key role in the transition from aquatic to terrestrial life for early plants. The study provides a detailed timeline of archaeplastid evolution, showing that multicellularity and land plant evolution occurred during the Cryogenian, consistent with the Snowball Earth hypothesis. The results are compatible with the hypothesis that ancient glaciations facilitated the origin of multicellularity in plants. The study also shows that the Cryogenian period was a critical time for the evolution of multicellularity and plant terrestrialization, with the emergence of multicellular algae and the first land plants occurring during this period. The findings suggest that the Cryogenian was a pivotal time in the history of life on Earth, with the development of multicellularity and land plants being closely linked to the Snowball Earth events. The study provides a comprehensive understanding of the evolutionary history of Archaeplastida, showing that the Cryogenian was a key period in the development of multicellularity and plant terrestrialization. The results support the hypothesis that the Cryogenian period was a critical time for the evolution of multicellularity and the transition