Monocots are a group of flowering plants that produce a single first leaf (cotyledon) as their seeds germinate. Eudicots (frequently referred to simply as dicots) produce two cotyledons. In addition to this feature, monocots and eudicots can be distinguished by several anatomical and morphological features. One of these features is the arrangement of tissues in the stem. In monocots, the vascular tissue is arranged in distinct bundles that are scattered throughout the stem. The xylem is located on the side of the vascular bundles that face the center of the stem and can be identified by the large, hollow vessel elements that stain differently due to their secondary walls. In the half of the bundle that faces the exterior is the phloem, which contains sieve tube elements and their accompanying companion cells. The phloem is capped by a clump of fibers called the phloem fibers. The vascular bundles are arranged throughout the ground tissue in concentric circles with xylem facing inward.
Vascular bundles in monocots are called closed vascular bundles, as they will not go on to form secondary tissues (no residual procambium).
In the above of the vascular bundle on the left, label the xylem, phloem, a vessel element, sieve tube element, and companion cell.