chestnut oak
芧 refers specifically to the chestnut oak, a type of oak tree that produces chestnut-like acorns.
芧 combines the grass radical 艹 with 予, which likely contributes a phonetic element. The character is used for a specific plant name, but the exact historical development is uncertain.
The grass radical 艹 on top suggests a plant, and the lower part 予 looks like a sturdy trunk with branches. Picture a chestnut oak with its distinctive leaves and acorns.
For チョ, imagine a chestnut oak tree with a distinctive 'cho' sound when the wind blows through its leaves: cho -> チョ.