Amphivasal

Amphivasal is a term used in botany to describe a vascular bundle arrangement where the xylem is located on both sides of the phloem. This is a less common arrangement compared to collateral, where xylem and phloem are side-by-side, or bicollateral, where phloem is on both sides of the xylem. In amphivasal bundles, the phloem forms a cylinder or sheath around the xylem.

This specific arrangement is typically found in certain herbaceous dicotyledonous plants, particularly within the stems of some families like the Solanaceae (nightshade family) and the Convolvulaceae (morning glory family). The functional significance of the amphivasal arrangement is not fully understood, but it is thought to play a role in the transport of water and nutrients, potentially offering increased structural support or protection to the vascular tissues. Studying these unique vascular patterns contributes to our understanding of plant anatomy and evolution.