Comment on «Microlepia burmasia sp. nov., a new fern species from mid-Cretaceous Kachin amber of norther Myanmar (Dennstaedtiaceae, Polypodiales) » [Cretaceous Research 143 (2023) 105417]

Abstract

“Microlepia” burmasia is a recently described eupolypod fern from mid-Cretaceous Burmese amber by Long et al. (2023). According to the latest taxonomic system of ferns, “M.” burmasia belongs to the Dennstaedtiaceae, Polypodiales. Discovery of “M.” burmasia means the origin of the genus can be pushed back by at least 99 Ma. The specimen provides new information on the floral diversity of the Kachin amber forest and new insight to the origin of Microlepia and Dennstaedtiaceae (Long et al., 2023). However, a careful review of the illustrations and descriptions of the sporangium and spore in the manuscript showed that the polar axial length and equatorial length of the spores were three to six times that of the spores in the extant and fossil Microlepia species, and nearly the same size as the sporangium, and the sporangium morphology and spore size are very different from that of any other polypod species. In an effort to further investigate the systematic position of “Microlepia” burmasia, its spore morphology and size were compared with those of the entire Dennstaedtiaceae and to all fern families possessing trilete spores. Comparative analyses reveal some similarities only with Anemia subgenus Coptophyllum (Anemiaceae). However, the sporangium morphology of “Microlepia” burmasia does not align with Anemiaceae. Given these discrepancies, it is recommended to reconsider the placement of “Microlepia” burmasia within Polypodiales and its systematic placement needs further study.