#xylem

• Actinostele — An archaic type of vascular cylinder (stele) characteristic of the stems and roots of primitive vascular plants (such as pteridophytes), representing a structural variety of protostele. In cross-section, the central xylem is not circular but features ridges or arms arranged in a radiating (star-like) manner, being fully encircled by a peripheral band of phloem, a configuration optimizing mechanical resistance and sap conduction.
• Sapwood — The outer, younger, and less dense zone of the woody cylinder in tree stems and roots, located immediately beneath the bark (cambium). Sapwood consists of living cells with an active physiological role, responsible for conducting raw sap from the roots to the leaves and storing reserve substances, gradually converting into heartwood as the tree ages.
• Amphiphloic — Having or characterized by the presence of phloem tissue on both sides of the xylem; an adjective used in plant anatomy to define a structural type of central cylinder (amphiphloic siphonostele or solenostele), commonly found in ferns, where the central pith is successively surrounded by an inner ring of phloem, a central ring of xylem, and an outer ring of phloem.