J Syst Evol ›› 2021, Vol. 59 ›› Issue (2): 375-387.DOI: 10.1111/jse.12532

• Research Articles • Previous Articles     Next Articles

Plenasium xiei sp. nov. from the Cretaceous of Northeast China: Additional evidence for the longevity of osmundaceous ferns

Ye‐Ming Cheng1†*, Feng‐Xiang Liu1†, Ning Tian2, Yue‐Gao Jin1, and Tong‐Xing Sun3*   

  1. 1Department of Collection Management, The Geological Museum of China, Beijing 100034, China
    2College of Palaeontology, Shenyang Normal University, Shenyang 110034, China
    3School of Marine and Biological Engineering, Yancheng Teachers University, Yancheng 224002, Jiangsu, China
  • Received:2019-04-04 Accepted:2019-07-01 Online:2019-07-22 Published:2021-03-01

Abstract: A new species of the Osmundaceae, Plenasium xiei sp. nov., is herein described from the Cretaceous of Northeast China. The specimens examined here represent the earliest unequivocal record of the extant genus Plenasium in Eurasia based on fossil rhizomes. The rhizome consists of a central stem with a mantle of petiole bases and adventitious roots. The stem contains an ectophloic‐dictyoxylic siphonostele and a two‐layered cortex. The C‐shaped leaf trace bears two protoxylem bundles at the point of separation from the stele. The pith is heterogeneous. The parenchymatous inner cortex is thinner than the sclerenchymatous outer cortex. Lobed sclerenchyma bands occur at the adaxial sides of the stem xylem strands, in the concavity of the leaf trace, and along the adaxial side of the vascular bundles of the petiole base. In distal petiole portions, the sclerenchyma band splits into several groups in the transverse view. Sclerenchyma rings are heterogeneous with an abaxial sclerenchymatous arc of thick‐walled fibers. Numerous sclerenchyma strands of thick‐walled fibers appear in the petiolar inner cortex and the stipular wing. These fossils provide unambiguous evidence for the existence of subgenus Plenasium of modern Plenasium by at least the Late Cretaceous, demonstrating the longevity of this extant subgenus. Altogether the leaf and rhizome fossil records of Plenasium indicate that this genus was widely distributed across North America and Eurasia from the Early Cretaceous to the Early Cenozoic, followed by a range restriction to Eurasia in the Late Cenozoic. Extant Plenasium species are only known from East and Southeast Asia.

Key words: anatomy, Cretaceous, Heilongjiang, Osmundaceae, paleobiogeography, Plenasium, rhizome