The Leaf Length-Width Method Is Applicable to Compound Leaves of Diverse Forms

To estimate leaf area, the length-width method, also called the Montgomery equation, has been widely used. It is an empirical formula stating that within a given species, the area of a leaf is proportional to the product of its length and width. Although the formula is known to be applicable to a variety of simple leaves and leaflets, its applicability to compound leaves has only been investigated on a limited range of leaf forms and economically important crops. In this study, we investigated whether this method is broadly applicable to compound leaves of diverse forms. We measured 20 compound-leaved species including various leaf shapes (ternate, biternate, triternate, palmate, pedate, and pinnate leaves) as well as life forms (trees, herbs, and woody and herbaceous lianas). Our data cover diverse taxa, including both Ranunculales and core eudicots (Fabales, Rosales, Fagales, Vitales, Apiales, Lamiales, Asterales, and Dipsacales). The results show that the length-width method is applicable to all types of compound leaves investigated (slope [i.e., Montgomery parameter]: 0.298–1.035; R2 = 0.928–0.996). These results indicate that a compound leaf can be considered equivalent to a simple lobed leaf when applying the length-width method.