Developmental studies of the leaves of Sagittaria latifolia and their relationship to the leaf-base theory of monocotyledonous leaf morphology

Abstract

The adult sagittate leaf of Sagittaria latifolia Willd. (Alismataceae) is an example of a monocotyledonous leaf which is differentiated into distinct blade, petiole, and sheath regions. Unlike some bladed monocotyledonous leaves in which the lamina has been shown to be a modification of the leaf base, the adult arrowhead-shaped leaf has no radial precursor tip which facilitates its evaluation in terms of the leaf-base theory. However, the scale and linear leaves of this plant are each comprised of a dorsiventral leaf base and a radially symmetrical upper leaf zone. These leaves are found in a heteroblastic series beginning with reduced scale leaves. Comparative morphological studies of the scale and linear leaves as well as evidence from scanning and light microscopy of the arrowhead-shaped leaves indicate that the lamina of the sagittate leaf is derived from the distal portion of the upper leaf zone. Similarities in internal structure between the unifacial distal region of the linear leaf and the dorsiventral sagittate blade also support this observation. Therefore, Knoll's leaf-base theory of monocotyledonous leaf morphology can be expanded to accommodate the sagittate leaf.