bean, nutmeg
荳 centers on a specific plant product: a bean or, more specifically, nutmeg. The meaning is narrow and botanical, referring to a particular seed or spice.
荳 combines the grass radical 艹 with 豆 (bean), suggesting a plant that produces beans or bean-like seeds. The specific association with nutmeg likely comes from its seed-like appearance.
The grass radical 艹 sits above a bean 豆, like a bean plant growing in a field. Think of nutmeg as a special bean from a plant.
For トウ, imagine a toe bean: a tiny bean-shaped toe on a plant. Toe -> トウ, and the plant grows toe beans.