There is a particular plant, often seen as menuki and sometimes on tsuba.   One respected Japanese authority translated it as 'Geranium' - such as an African Geranium. I couldn't find any images of Japanese Geraniums that seemed closer. When shown an old painting of 'wild ginger' aka. Wasabi, which is 山葵 [literally Mountain Hollyhock], i began to question that description.   Here is an auction for menuki, where I believe the seller IDs it as 山葵 wasabi. https://page.auctions.yahoo.co.jp/jp/a