Date Published: July 7, 2017
Publisher: Public Library of Science
Author(s): Yunjun Bai, Xiaoqiang Li, William Oki Wong.
Previously, the identification of fossil Pseudolarix at the species level has been based on the morphology of the bract-scale complex of the seed cone. The morphological consistence of fossils through most of the Cenozoic with extant P. amabilis has led them to be considered conspecific, suggesting that P. amabilis is an extraordinary example of morphological stasis. However, the lack of cuticular evidence, especially for the leaf-homologous bract, reduces the accuracy of fossil identification based on morphology, thus weakening the evidence for morphological stasis in P. amabilis. For the first time, we provide cuticular evidence of the bract-scale of fossil P. amabilis based on the bract-scale complex from the late Miocene Shengxian Formation, Zhejiang, East China, which improves the identification accuracy and reinforces the concept of morphological stasis in this species. Second, we preliminarily reveal the niche stability of P. amabilis, which corresponds to its morphological stasis. Finally, we infer that the late Miocene forest containing P. amabilis in Zhejiang was an evergreen sclerophyllous broad-leaved or mixed mesophytic forest, which combined with the evergreen broad-leaved forest suggested by previous megafossil studies, indicates the occurrence of vertical vegetation zonation.
Today, Pseudolarix Gordon (Pinaceae) is a monotypic genus represented by the single species P. amabilis (Nelson) Rehder . The unique biological features of Pseudolarix that distinguish it from other members of the Pinaceae are its combination of deciduous bract-scale complexes and needles and branch dimorphism. The dimorphic branching system is characterized by needles borne helically in long shoots (leading shoots) and fascicularly in short shoots (brachioblasts) .
The described fossil bract-scale complexes were collected from the Shengxian Formation outcrop near Jiahua village, Tiantai County, Zhejiang, East China (29.2°N, 121.2°E; Fig 2). 40Ar-39Ar dating indicates the age of the Shengxian Formation to be 10.5±0.5 Ma . The herbarium sheets used for comparison were obtained from the PE Herbarium, Institute of Botany, Chinese Academy of Sciences, Beijing, China. These herbarium sheets include P. amabilis (Col. Nos. 18850, 74383, 1169, 18591, 28492), Cedrus deodara (Col. No. 2763), Abies alba (Col. No. N/A), Araucaria cunninghamii (Col. No. 235) and Agathis dammara (Col. No. 2021).