agueweed, valeriana villosa, climbing plant
蕑 refers to specific plants: agueweed, a type of valerian (Valeriana villosa), and climbing plants in general. The core idea is a herbaceous or vining plant.
蕑 combines the plant radical 艹 with 閒, which likely provides the sound. The character is used for specific plant names, but its detailed historical development is uncertain.
The grass top 艹 over 閒 suggests a plant that grows in gaps or spaces, like a climbing vine or a weedy herb such as agueweed.
For カン, imagine a can of climbing plant seeds: can -> カン, and the plant grows out of the can.