Molecular clocks vs. fossils, that is. In his commentary, “Timescales and timetrees” (New Phytologist, September 2, 2011), Paul Kendrick explains,
Results are controversial, indicating substantially earlier origins of land plants and flowering plants than is supported by direct fossil evidence.
One of the most interesting and controversial nodes to calibrate is the origin of land plants. Clarke et al. give a mean estimate for land plants of 670 Ma (Cryogenian) (CI 815–568 Ma: Cryogenian through early Cambrian). Previous molecular calibrations reviewed in Magallón & Hilu (2009) present two contrasting views. One set of studies indicates that land plants originated during the late Neoproterozoic, with values typically falling within a range of c. 850–542 Ma (Cryogenian to Ediacaran). Others are indicative of an early Palaeozoic radiation during the late Cambrian through Silurian Periods. Clarke et al. therefore favour an early origin of land plants, and the divergence of basal plant lineages (i.e. major clades of bryophytes) spans a much greater interval of time than in previous studies (Ediacaran through Ordovician, some 236 Ma).