Biomechanical analysis of a Palaeozoic gymnosperm stem

Biomechanical parameters are presented for permineralized Calamopitys stems from the Lower Carboniferous of central Germany. A centrisymmetrical model of the fossilized plant stem as viewed in transverse section suggests that slender stems up to 15 mm in diameter were semi-self-supporting. Analysis of the contribution of various tissue types to the mechanical stability of the stem shows that the outer cortex (alternating bands of fibres and parenchyma) was the principal contributor to flexural stiffness of the stem followed by the multi-fascicular petiole bundles. The cylinder of wood located near to the centre of the stem is of relatively minor structural importance. The slender Calamopitys stem differs in mechanical terms from the plesiomorphic arrangement observed in aneurophytalean progymnosperms as a result of the support provided by numerous petiolar bundles. This contrasts with the structural divergence observed in Lyginopteris oldhamia, which resulted from an increased diameter of the procambium and larger role of the wood cylinder for mechanical support.