The Silurian and Devonian plant fossil record is the basis for our understanding of the early evolution of land plants, yet our appreciation of early global phytogeographic evolution has been constrained by the focus of most studies on deposits from Europe, North America, and, more recently, South China. Devonian plants have been recorded rarely from northeastern China, and among previous records, few plants have been illustrated and formally described. In this article, megafossil plants representing a Late Devonian-aged (probably Famennian) flora are described from a locality at northern Sonid Zuoqi, Inner Mongolia, NE China. The flora includes Melvillipteris sonidia new species, Archaeopteris sp., and fragments of some other plants. The new plant shows main axes and two orders of lateral branches. The first-order branches of this plant show a typical zigzag appearance and are borne in pairs on main axes. Second-order branches are straight or slightly flexed, and are borne helically or alternately on first-order branches. Sterile ultimate appendages and fertile structures of M. sonidia n. sp. are borne alternately on second-order branches. An associated palynological assemblage, as well as U-Pb ages of detrital zircon grains from adjacent horizons, are also reported, indicating a Late Devonian age in accord with the megafossil plants. The present study contributes to our appreciation of the Devonian floristic diversity of the Xing'an Block, and, through our review of the record of early vascular plants from NE China, more broadly to the understanding of the mid-latitude vegetation of the Northern Hemisphere during the Late Devonian.

The fusuline genera Thailandina Toriyama and Kanmera, 1968 and Neothailandina Toriyama and Kanmera, 1968 were established by Toriyama and Kanmera (1968) based on material from the Khao Phlong Phrab section of the Permian Rat Buri Limestone in central Thailand that is currently assigned to the Khao Khad Formation of the Saraburi Group (Ueno and Charoentitirat, 2011). These fusuline genera are peculiar in having parachomata and replaced tests by secondary mineralization. Moreover, Neothailandina was described to have a test with transverse septula, considered to be characteristic for Neoschwagerinidae. Based on these remarkable test features, Toriyama and Kanmera (1968) newly introduced the subfamily Thailandininae to accommodate these two new genera and assigned it to the Neoschwagerinidae, despite the lack of septula in Thailandina. Later, Kobayashi et al. (2010) argued that Thailandina and Neothailandina are just a mixed grouping of several known genera of schwagerinids, verbeekinids, and neoschwagerinids that are too altered by recrystallization to be recognizable, and rejected the taxonomic validity of these two genera as well as Thailandininae.

The Khao Phlong Phrab section represents one of the standard late Cisuralian−Guadalupian (late early−middle Permian) fusuline successions in the eastern Paleotethys (Zhang and Wang, 2018) and contains not only Thailandina and Neothailandina but also abundant schwagerinid, verbeekinid, and neoschwagerinid fusulines (Toriyama, 1975; Fig. 1). I investigated the original specimens described by Toriyama and Kanmera (1968) and Toriyama (1975) from the section that are housed in the Department of Earth and Planetary Sciences of Kyushu University, Japan. I found that most of the grounds for Kobayashi et al.'s (2010) arguments to regard the thailandinin genera as taxonomically invalid are not supported by observations on these specimens as explained in the account that follows. In this taxonomic note, I propose that Thailandina and Neothailandina, and their family Thailandinidae, should be retained as valid taxonomic groups.