Abstract
The vascular system of monocotyledons, including Commelinaceae, has been studied since the 19th century, but to date, the proposed vascular architecture models consist of schematic representations partially based on the authors' interpretation. One of the greatest difficulties in studying these systems is the large number of vascular bundles and the complexity of their connections, especially in the monocotyledons which have a nodal vascular plexus. In this study, shoot apex samples of 14 species of Commelinaceae were submitted to three-dimensional analyses (confocal microscopy, X-ray microtomography, graphic vectorization, and whole-mount diaphanization), as well as conventional techniques in plant anatomy. Based on the results, a previously unreported category of bundles is described in Commelinaceae for the first time, as well as the fact that peripheral bundles are not interrupted or end blindly in the periphery of the pith, as previously thought. With this new interpretation of the vascular architecture, three patterns of nodal vascular plexus are proposed: 1) in the first pattern the internal nodal vascular plexus (IVP) forms a continuous cylinder and does not connect to the external nodal vascular plexus (EVP); 2) the IVP forms a cylinder divided into two columns and does not connect to the EVP and 3) the IVP forms a cylinder connected to the EVP. The first description of central bundles in the Commelinaceae might suggests their existence in closely related groups, such as the remaining four families of Commelinales (i.e., Haemodoraceae, Hanguanaceae, Philydraceae, and Pontederiaceae), and even in other distantly related groups of monocotyledons.
Highlights
The vascular bundles that constitute the sympodia can be subdivided into three categories: 1) Major bundles- first bundles to be originated, which occupy the medial region of the pith, along the internode; 2) Minor bundles- bundles that arise between the major bundles and occupy the periphery of the pith; and 3) Central bundles—of the pith, resulting from the fusion of major bundles in the internal nodal vascular plexus (IVP)
Internal vascular system—constituted of sympodia and central bundles which connect in the internal region of the nodes, forming the IVP
External vascular system—constituted of sympodia and cauline bundle, which connect in the external region of the nodes to form the external nodal vascular plexus (EVP)
Summary
The funders had no role in study design, Monocotyledons are one of the most diverse herbaceous lineages of flowering plants, and its primary vascular system of the shoot is composed of bundles that vary in size, shape, organization and distribution, and can be continuous (i.e, sympodial bundles) or discontinuous (i.e., cauline bundle) [1,2,3,4]. Monocotyledons have three types of bundles: major (or large/larger), minor (or small/smaller) and cauline [1,2,4,5]. The major and minor bundles form leaf traces. A new interpretation of vascular system in Commelinaceae data collection and analysis, decision to publish, or preparation of the manuscript
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