Vascular organization and wood anatomy of secondary stems of Piper hieronymi C. DC. (Piperaceae)

Abstract

Piper hieronymi is a shrub or small tree that inhabits the forests of Jujuy, Salta, Tucumán and Misiones, in Argentina. The stems and branches bear greatly thickened nodes, and from an anatomical viewpoint their vascular bundles exhibit a polycyclic arrangement. This work aims to characterize the vascular organization and the wood of secondary stems of P. hieronymi. As in other Piper species, the vascular cylinder includes two systems, a central system (SVM) and a peripheral one (SVP). Both comprise open bicollateral bundles, associated with fiber caps. The SVM has one or sometimes two cycles of vascular bundles scattered in lignified parenchymatic pith. Differences in SVM bundle arrangement were observed at node and internode level, as these bundles are responsible for branch vascularization. The SVP occupies most of the stem thickness. It has alternating elongated vascular bundles and interfascicular parenchymatic rays, composed mostly of upright cells. In addition, the bundles may be bifurcated by development of fascicular rays. The wood is diffuse-porous, with vessels in short multiple radials, arranged in a radial pattern, simple perforation plates, alternate or scalariform intervessel pits, vasicentric axial parenchyma, and with some differences between SVM and SVP. The secondary stem anatomy of P. hieronymi shares similarities with both shrubby and climber species, although so far, SVP bundle bifurcation has only been recorded for shrubby or small tree species.