This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
楉 combines 木 (tree) with 若, which likely contributes the sound. The exact historical development is uncertain, and the character is rare.
The tree radical 木 beside 若 suggests a type of tree or plant, but the exact meaning is uncertain. Picture a rare tree named after the sound 若.
For ジャク, imagine a rare tree called a 'jack tree' in a story: jack -> ジャク, and the tree radical 木 helps you remember it's a plant.