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Cooksonia One of the earliest of land plants, known from the late Silurian and early Devonian (400 Ma ago), which is believed to be ancestral to all vascular plants. A few centimetres tall, it was upright, dichotomously branching, produced thick-walled spores, possessed a cuticle and stomata to control the passage of gases, and an underground rooting portion, the rhizome. Long suspected of being a vascular plant, the presence of a variety of conducting elements was confirmed in the Lower Devonian C. pertoni in 1992 (by D. Edwards, K. L. Davies, and L. Axe). Two species are known: C. pertoni and C. hemispherica (Silurian), the latter being the first representative of the order Rhyniopsida. Cooksonia may share a common ancestor with the club mosses or be ancestral to them.

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