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Concept
Lepidodendron
Résumé
Lepidodendron is an extinct genus of primitive vascular plants belonging to order Lepidodendrales, part of a group of Lycopodiopsida known as scale trees or arborescent lycophytes, They were part of the coal forest flora. They sometimes reached heights of , and the trunks were often over in diameter. They thrived during the Carboniferous Period (358.9 to 298.9 million years ago). Sometimes erroneously called "giant club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses. Within the form classification system used within paleobotany, Lepidodendron is both used for the whole plant as well as specifically the stems and leaves.
The name Lepidodendron comes from the Greek λεπίς lepis, scale, and δένδρον dendron, tree.
Lepidodendron species were comparable in size to modern trees. The plants had tapering trunks as wide as at their base that rose to about and even , arising from an underground system of horizontally spreading branches that were covered with many rootlets. Though the height of the trees make the plants similar to modern trees, the constant dichotomy of branches created a habit that contrasts with that of modern trees. At the ends of branches were oval-shaped cones that had a similar shape to modern cones of a spruce or fir.
The stem of the trees had a unifacial vascular cambium, contrasting with the bifacial vascular cambium of modern trees. Though the bifacial cambium of modern trees produces both secondary phloem and xylem, the unifacial cambium of Lepidodendron trees produced only secondary xylem. As the trees aged, the wood produced by the unifacial cambium decreased towards the top of the plant such that terminal twigs resembled young Lepidodendron stems. Compared to modern trees, the stems and branches of the trees contained little wood with the majority of mature stems consisting of a massive cortical meristem. The nearly-uniform growth of this cortical tissue indicates no difference in growth during changing seasons, and the absence of dormant buds further indicates the lack of seasonality in Lepidodendron species.
Source officielle
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