This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 莂 is uncertain. It visually combines the grass radical 艹 with 別, but the exact development is unclear.
The top grass radical 艹 and the bottom 別 (separate) might suggest separating plants, but the meaning is too uncertain for a reliable mnemonic.
For ヘツ, imagine a rare plant labeled with a made-up name: 'hetsu' grass. The sound 'hetsu' cues ヘツ, and the grass radical ties it to the kanji shape.