edible greens, amaranth
莧 centers on a specific edible plant: amaranth, a type of leafy green used as food.
莧 combines the grass radical 艹 with 見, likely as a phono-semantic compound where 見 hints at the sound and 艹 indicates a plant. The exact historical development is uncertain.
The grass top 艹 over 見 (see) suggests a plant you can easily spot: amaranth, a common edible green.
For カン, imagine a can of amaranth greens: can -> カン, and you see the plant inside.