Vegetative Characters, Growth Habit and Microsporangiate Strobilus of Lycopsid Minostrobus chaohuensis
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.
A Lycopsid with Novel Reproductive Structures from the Upper Devonian of Jiangsu, China
A new lycopsid is described from the Upper Devonian (Famennian) of Wuxi, Jiangsu Province, China. It has isodichotomous branches and long leaves with spiny margins. Two types of fertile structures are present. Megasporangia‐bearing conelike structures are found at dichotomies of the branches, having large, densely inserted leaves with enlarged bases, bearing adaxial sporangia containing large megaspores. The other type are terminal cones, having slender, closely inserted leaves, and dark carbonaceous areas adjacent to the axis are interpreted as the remains of microsporangia. The new plant closely resembles lycopsids previously reported from the Middle and lower Upper Devonian of China, but the reproductive characters are more advanced. It demonstrates that the early history of large lycopsids is more complex than has been recognized. We name the new plant Wuxia bistrobilata gen. et sp. nov.
Le genre Leptophloeum Dawson, 1862 du Dévonien
Resume L'etude de nombreuses empreintes rapportees augenre Leptophloeum , provenant notamment du Kazakhstan et d'Afrique du Sud, a permis de preciser la morphologie des feuilles et d'interpreter les empreintes des coussiets foliaires. Une revision des especes est effectuee. Une comparaison du genre Leptophloeum du Devonien avec le genre Lycopodiopsis du Permien conduit a la distinction d'un nouvel ordre: celui des Leptophloeodendrales regroupant ces deux genres.