hemp palm
椶 refers specifically to the hemp palm, a type of palm tree. Its meaning is narrow and botanical, without broader abstract extensions.
椶 combines 木 (tree) with 㚇, which likely contributes the sound. The character was created to name a specific palm tree, but the detailed origin of 㚇 is uncertain.
The left side is a tree 木, and the right side 㚇 looks like a palm frond with hanging fibers. Picture a hemp palm tree with its distinctive fibrous leaves.
For シュ, imagine a shoe made of hemp palm fibers: shoe -> シュ, and the tree provides the material.