An acrocarpous moss in Cretaceous amber from Myanmar

• A bryophyte inclusion in a piece of Cretaceous Burmese amber is described.
• The sterile gametophyte is assigned to the form genus Calymperites.
• Calymperites burmensis sp. nov. has awned leaves with a single costa.
• The basal leaf cells are hyaline.
• The lamina consists of bulging, quadrate-rectangular cells.

Recent studies have indicated considerable changes in the lineage composition of mosses during the Cretaceous terrestrial revolution. However, Cretaceous moss fossils are generally rare. Here we describe a sterile gametophyte fragment of an acrocarpous moss preserved in mid-Cretaceous amber from Myanmar. The fossil at hand is assigned to the extant Dicranales based on its narrowly lanceolate, awned leaves with a single costa, quadrate-rectangular, bulging leaf cells forming a serrate leaf margin, and oblong-ovate leaf bases with hyaline, rectangular cells. The protruding cells of the awns point to the possibility that they previously carried gemmae, as is seen in numerous extant representatives of the Calymperaceae genera Calymperes and Syrrhopodon. The fossil differs from both genera by its indistinctly separated hyaline basal leaf cells, and is placed in the form genus Calymperites as C. burmensis sp. nov.