Morphology and ultrastructure of Middle Devonian dispersed megaspores from Qujing, Yunnan, Southwest China

• Published in: Review of Palaeobotany and Palynology
• Main Authors: Peng, Huiping, Liu, Feng, Zhu, Huaicheng
• Format: Report
• Language: English
• Published: ELSEVIER SCIENCE BV 2016
• Subjects: WALL ULTRASTRUCTURE; NORTHERN POLAND; SEED-MEGASPORES; SPORES; HETEROSPORY; PLANTS; Plant Sciences; Paleontology; Arctic; Canada
• Online Access: http://ir.nigpas.ac.cn/handle/332004/20873; https://doi.org/10.1016/j.revpalbo.2016.08.010

Lycopsid megaspores isolated from the Middle Devonian, Givetian, Shangshuanghe Formation at Qujing in Yunnan, Southwest China, were identified and illustrated using fluorescence microscopy (FLM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three species (Longhuashanispora reticuloides Lu et Ouyang, 1978, Ocksisporites maclarenii Chaloner 1959, and Cereusisporites mirabilis Lu et Ouyang, 1978) are described. L. reticuloides is azonate. Both proximal and distal exines of L. reticuloides consist of a thin basal lamina with a high density of sporopollenin units, a loose spongy region with different types of voids, and a solid region with some processes. It is intriguing that the processes of L. reticuloides usually have a large cavity at their base. Coronispora sinica Lu et Ouyang ex Jansonius et Hills, 1992 is a junior synonym of Ocksisporites maclarenii Chaloner 1959. The other species currently accommodated in Coronispora is transferred to Ocksisporites resulting in the new combination O. variabilis (Fuglewicz et Prejbisz) comb. nov. O. maclarenii is zonate. The proximal exine of O. maclarenii primarily consists of a solid region while the distal exine is mainly composed of a loose spongy region. C mirabilis is also zonate. Both proximal and distal exines of C. mirabilis could be divisible into a thin basal lamina, the first solid region with or without small voids, a loose spongy region with different types of voids, and the second solid region with some processes. Both proximal and distal processes of C. mirabilis have large internal cavities, although the distal processes are higher and more robust. Comparisons with in situ spores produced by plant fossils recovered from coeval horizons in adjoining region suggest that Longhuashanispora reticuloides shares ultrastructural and morphological characteristics of the in situ spores yielded by both heterosporous and homosporous ligulate lycopsids. Its parent plant probably represents a transitional form from the homosporous ligulate to the heterosporous ligulate lycopsids. It supports the previous conclusion that the homosporous ligulate lycopsid lineage and the heterosporous ligulate lycopsid lineage have diverged in the late Middle Devonian. The parent plants of O. maclarenii and C mirabilis may have been a type of herbaceous lycopsid, which is rarely preserved as a fossil. The presence of the genus Ocksisporites in South China, Arctic Canada, and northern Poland indicates that in the Middle Devonian a migration pathway for plants existed between South China and Laurasia. (C) 2016 Elsevier B.V. All rights reserved.