Abstract
Late Devonian Minostrobus chaohuensis is one of the earliest monosporangiate-strobilate isoetaleans. Based on new material of this plant, the vegetative axis and microsporangiate strobilus are studied in detail, and the whole plant knowledge is summarized. The vegetative axis is isotomously branched. The stem is up to 55 mm in diameter with helically arranged leaf cushions. Stems and thick branches bear long fusiform leaf cushions and interareas with vertical linear ornamentations. A ligule pit, oblanceolate leaf scar, and vascular bundle scar appear on the leaf cushion. Distal axes have persistent lanceolate leaves and rhombic leaf bases. The microsporangiate strobilus is cylindrical in shape, possesses sporophyll with alate pedicel and long triangular lamina, uniseriate sporangial wall, subarchesporial pad inside the sporangium, and microspore with cingulum. Based on comparisons with other isoetaleans, the usage of the terms “leaf cushion” and “leaf base” is discussed, and Minostrobus chaohuensis is considered as a tree-like lycopsid. It suggests that arborescent isoetaleans with monosporangiate strobili had appeared and diversified in the Late Devonian. The multi-dichotomous branching system of Minostrobus provides new data on the evolution of growth architecture in rhizomorphic lycopsids.
Highlights
Arborescent lycopsids of Isoëtales sensu lato Meyen, especially the relatively derived clade with monosporangiate strobili (Dichostrobiles DiMichele and Bateman), are the most conspicuous plants of the Carboniferous landscape around the world [1], [2]
Minostrobus chaohuensis Wang was reported from the Upper Devonian Wutong (Wutung) Formation of Chaohu City, Anhui Province, South China, and was established on the basis of PLOS ONE | DOI:10.1371/journal.pone
Evident interareas with vertical linear ornamentations among the leaf cushions exist on axes thicker than 10 mm (Fig. 1B, F, H), and their area is in proportion to the width of axes (Fig. 1A, C, F)
Summary
Arborescent lycopsids of Isoëtales sensu lato Meyen, especially the relatively derived clade with monosporangiate strobili (Dichostrobiles DiMichele and Bateman), are the most conspicuous plants of the Carboniferous landscape around the world [1], [2]. Sublepidodendron (Nathorst) Hirmer as a member of Dichostrobiles flourished in the Late Devonian of South China [3,4,5]. In this study, another isoetalean with monosporangiate strobili, Minostrobus Wang, is suggested to have arborescent habit. Another isoetalean with monosporangiate strobili, Minostrobus Wang, is suggested to have arborescent habit Detailed research on this plant adds to our knowledge of the evolution of lycopsids in the Devonian. Minostrobus chaohuensis Wang was reported from the Upper Devonian Wutong (Wutung) Formation of Chaohu City, Anhui Province, South China, and was established on the basis of PLOS ONE | DOI:10.1371/journal.pone.0122167 March 27, 2015
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