species of yew
棐 refers specifically to a species of yew tree. The meaning is narrow and botanical, without broader abstract extensions.
棐 combines 非 (possibly phonetic) with 木 (tree), suggesting a tree name. The exact historical development is uncertain.
The top 非 looks like opposing wings or branches, and the bottom 木 is a tree. Imagine a yew tree with distinctive spreading, wing-like branches.
For ヒ, picture a yew tree shaped like the letter H: H -> ヒ, with the tree's branches forming the crossbar.