The pattern of vascular deployment near the pulvinus of the solar-tracking leaf of Lavatera cretica (Malvaceae)

Abstract

Distinguishable files of xylem and phloem elements that originate in first-order branches of the seven palmate major veins of Lavatera cretica leaves become separated from files unique to the radially aligned sections of the same veins before entering the pulvinus at the distal end of the petiole. The major veins initially merge to form a double coaxial tube: the outer cylinder comprises files unique to the major veins and the inner cylinder comprises files from lateral branches. Subsequent splitting, unfolding, and recombining of these cylinders results in the single narrow flexible tube constituting the hinge of the pulvinus. Proximal to this point, in L. cretica, the files reseparate into six alternately large and small petiolar bundles. The observed vascular pattern offers a means whereby signals from the lamina that elicit sun-tracking movements by the pulvinus can be integrated.