The Sunflower is an accessory that pets can wear in Nintendogs + Cats. It can be bought from Coletta for $8 once it has been unlocked with 6,600 Owner Points or by playing 23 days. It can be found on walks or via the Pedometer before you reach that many Owner Points or days. It looks like a sunflower.
3DS: "Set a cheery mood with this big, vibrant flower."