thorny shrub with yellow flowers
棫 refers to a specific thorny shrub with yellow flowers. The meaning is narrow and botanical, without a broader conceptual center.
棫 combines 木 (tree/wood) with 或, which likely contributes a phonetic element. The character is used for a specific plant name, but the exact historical development is uncertain.
The left side 木 suggests a woody plant, and the right side 或 looks like a protective enclosure. Picture a thorny shrub with yellow flowers growing inside a fenced area, its thorns guarding the bright blooms.
For ヨク, imagine a yoke of oxen trying to pull the thorny shrub out of the ground: yoke -> ヨク, and the shrub resists with its thorns.