Fig. 2.

Chronogram for hornworts and their outgroups obtained from mitochondrial and plastid sequences modeled under a relaxed uncorrelated log-normal clock. Node heights represent mean ages and bars the 95% highest posterior density intervals. Numbers represent the calibrations (Material and Methods): 1: Vascular plant divergence, 2: Anthoceros spore type A; 3: Notothylites nirulai fossil; and 4: fossil assigned to Phaeomegaceros sp. (Inset) Average values of atmospheric CO₂ (ppm) levels during the last 100 Mya (56, 57). In the Inset, highest posterior density age inferred for the pyrenoid-bearing clades: Anthoceros, Phaeoceros, Notothylas, Nothoceros, and Dendroceros (red) and their pyrenoidless sister clades, Paraphymatoceros and Megaceros (blue).