Functional differentiation between the inner and outer leaves in a mechanical support by a pseudostem of Veratrum album subsp. oxysepalum

Abstract The pseudostem of Veratrum album subsp. oxysepalum consists of radical leaves, which have tubular and concentrically aggregated petioles. We examined a hypothesis that the major role of the inner leaves is to raise the leaf blades higher for increased photosynthesis, while that of the outer leaves is to mechanically support the inner leaves at the expense of displaying their leaf blades. The removal of outer leaves resulted in the collapse of the remaining inner leaves, showing outer leaves provide important support for inner leaves. The estimation of mechanical properties for the constituting leaves revealed that inner leaves possess greater mass of leaf blades for their capacity of mechanical support them compared to outer leaves. These results uphold the hypothesis that the primary role of inner leaves is to display leaf blades for photosynthesis, while that for outer leaves is to mechanically support the less stable inner leaves.