This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 枛 is uncertain. It visually combines 木 (tree/wood) and 爪 (claw/nail), but the original meaning and component relationship are unclear.
The kanji has no clear meaning, so a mnemonic based on shape is not reliable. If needed, you could imagine a wooden claw (木 + 爪) as a placeholder, but this is not a real meaning.
For ソウ, imagine a saw (ソウ) cutting a wooden claw shape: saw -> ソウ, and the wood 木 and claw 爪 come together.