Radula heinrichsii (Radulaceae, Porellales), a leafy liverwort from the mid-Cretaceous of Myanmar

Abstract

With ca. 250 extant species, Radula is one of the largest genera of the Porellales and the sole extant genus of the leafy liverwort family Radulaceae, widely distributed around the world. The earliest fossils of Radula were described from the mid-Cretaceous Kachin amber of Myanmar, namely R. cretacea and R. heinrichsii. Here, we report two new exquisitely preserved specimens of R. heinrichsii from Kachin amber, yielding new morphological characters for an extended description of this taxon. Cladistic analysis based on a matrix of fourteen morphological characters and a molecular backbone constraint suggests its close relationship with extant species of Radula subgenus Amentuloradula. But due to distinctive morphological characters in R. heinrichsii and the younger estimated age for the crown group, it is likely that R. heinrichsii represents a stem group of the subgenus Amentuloradula. The genus Radula is characterized by a high degree of morphological homoplasy, which makes the assignment of fossils to this extant taxon difficult and requires profound knowledge of the morphology of fossils.