A New Species of Krameropteris (Dennstaedtiaceae) from Mid-Cretaceous Myanmar Amber

Krameropteris is an extinct fern genus found in mid-Cretaceous Myanmar amber, assigned to the Dennstaedtiaceae, with only one previously described species, i.e., K. resinatus. This study describes a new species, K. calophyllum, also preserved in Myanmar amber. The new species is characterized by branched venation with free veinlets terminating in thickened tips, multicellular hairs along the pinnule margins, and submarginal or medial exindusiate sori at the ends of veinlets. Its sporangia are polypod-type, producing trilete spores. This new species represents the second record of an extinct fern genus of the early-diverging Dennstaedtiaceae lineage found in Myanmar amber. Krameropteris calophyllum differs from K. resinatus in its pinnule epidermal characteristics and spore morphology, with the latter exhibiting a conspicuously ornamented perine, covered with sparse tubercles and ridges. The new species provides insights into potential herbivory interactions and the relationship between mid-Cretaceous polypod ferns and the smallest mite ever recorded. These findings suggest that Dennstaedtiaceae exhibited species-level diversity by the mid-Cretaceous, indicating an earlier origin of the family, potentially as early as the Early Jurassic, consistent with recent DNA-based time divergence estimates.