Three-dimensional structure of stem vascular connections with leaf and adventitious root in Asplundia brachypus (Drude) Harling (Cyclanthaceae)

Abstract

The monocotyledonous vascular system is complex in arrangement, and its anatomical study is relevant to understand sap conduction in the group and elucidate stelar terminological issues. This work aimed to characterize the three-dimensional structure of the stem vascular connections with the leaf and adventitious root in Asplundia brachypus (Drude) Harling (Cyclanthaceae). Three internodes from different individuals were serially cross-sectioned for the preparation, photomicrography and description of anatomical slides. Three-dimensional representations of leaf and root trace courses were produced using R software. Leaf and root traces are simple collateral bundles with tracheary elements of small diameter. Acropetally, leaf traces show a centrifugal course along the internode and tangentially incline at the nodal level. At the adventitious root level, root traces arrange in a root vascular plexus extending up- and downward, longitudinally delimited by parenchyma. The small diameter of tracheary elements in leaf and root traces, the course extension of leaf traces and the longitudinal discontinuity of root traces with axial vascular bundles indicate conductive safety at the stem vascular connections with the leaf and adventitious root in A. brachypus. The three-dimensional vascular arrangement in the stem was demonstrated using an alternative methodology in representing bundle courses, evidencing the misleading nature of the terms "atactostele" and "placostele", alternatively described as a monocot cyclostele.