1. If there is no cambium tissue between xylem and phloem, it is called a closed collateral vascular bundle. Closed collateral vascular bundles are present in the stem of monocots.
2. Cambium tissue between xylem and phloem is called free lateral vascular bundle. Free collateral vascular bundles are present in stems of dicots and gymnosperms.
3. Xylem in the middle and phloem on either side are called bilateral vascular bundles. Equilateral vascular bundles are found in stems of plants like gourd, pumpkin, cucumber etc.
4. If the xylem is in the center and the phloem surrounds it, it is hydrocentric or amphicribal. Hydrocentric vascular bundles are found in stems of plants like Lycopodium, Selaginella, Pteris etc.
5. If phloem is in the center and xylem surrounds it, it is called leptocentric or amphivesal. Leptocentric vascular bundles are found in stems of plants like Dracaena, Yucca etc.