Pith width, leaf size, and twig thickness.

Area of Science:

• Plant anatomy
• Woody plant biology
• Ecology

Background:

• Many woody plants support large leaves by thickening twigs.
• E. J. H. Corner's rule states twig diameter increases with leaf size.
• Pith is a low-cost tissue in twig centers.

Purpose of the Study:

• To test the hypothesis that pith width increases with leaf size in woody plants.
• To investigate the cost-effectiveness of pith tissue in supporting large leaves.
• To extend Corner's rule regarding twig diameter and leaf size.

Main Methods:

• Measured leaf sizes and twig cross-sectional areas (bark, xylem, pith) for 81 tree and shrub species.
• Utilized standardized major axis regressions and phylogenetically independent contrasts.
• Compared species trait values.

Main Results:

• Pith area significantly increases with leaf size, even after accounting for phylogeny.
• Twig diameter, bark, and wood thickness also increase with leaf size, supporting Corner's rule.
• Relative pith, wood, and bark areas showed greater variation in thicker twigs.

Conclusions:

• Investing in pith provides a cost-effective method for increasing twig circumference.
• Wider pith supports larger leaf attachment and enhances twig biomechanical strength.
• Pith tissue is crucial for supporting large leaves in woody plants.