Marchantites huolinhensis sp. nov. (Marchantiales) – A new fossil liverwort with gemma cups from the Lower Cretaceous of Inner Mongolia, China

A new fossil liverwort species Marchantites huolinhensis R.Y. Li & B.N. Sun sp. nov., is founded based on twenty-seven fossil specimens collected from the Lower Cretaceous Huolinhe Formation in Huolinhe Basin of Inner Mongolia, China. The fossil liverwort is characterized by thalloid and prostrate gametophyte, and elliptical–circular gemma cups. Thallus is strap-like, dichotomously branched and with prominent costa. Imbricate ventral scales are in two rows and smooth and unicellular rhizoids are produced in considerable numbers around the costa. Cells on prominent costa are elongated and parallel to the long axis of the thallus. The relatively complete gametophyte, gemma cups, ventral scales and rhizoids indicate that they were likely to be autochthonously buried in dysoxic or anoxic silty deposits. Marchantites huolinhensis, along with other fossil records from other localities and age, indicates that the Marchantiales was already diverse in the Early Cretaceous and its morphological evolution is very slow.