The Morphology and Anatomy of the Leaf of Moricandia arvensis (L.) DC. (Brassicaceae)

Abstract

Mature leaves of Moricandia arvensis (L.) DC. were examined with the light microscope to determine their vasculature and the spatial relationships of vascular bundles to the mesophyll. One median and two lateral leaf traces enter the sessile lamina at the node. Upon entering the lamina, the continuations of both lateral traces bifurcate unevenly. The outer, smaller branches divide further to innervate the basal portion of the lamina, while the inner, larger branches and the continuation of the median trace constitute the primary bundles of the midvein. As the midvein progresses acropetally in a prominent midrib, branches from the lateral primaries diverge outward and continue as secondary veins toward the margins. By the median level of the lamina, the lateral primaries themselves diverge outward as secondary veins. Above the divergence of the lateral primaries the midvein is represented solely by the median bundle. Tertiary veins arise from both secondaries and the midvein; other higher-order minor veins arise from all orders of veins. All major veins-primaries and secondaries-are associated with rib tissue. All minor veins are completely surrounded by a chlorenchymatous bundle sheath. The mesophyll of the typically bifacial leaf is composed of poorly defined layers of palisade and spongy parenchyma cells. In addition, two poorly defined layers of mesophyll occur in the plane of the minor venation. Extensive lateral contact exists between contiguous mesophyll cells at all levels of the lamina.