If you are looking for truly large tubers, Marah species (Cucurbitaceae) have human-body-sized tubers, well buried underground. I dug a 10 year old tuber out of my garden one year, which took me 2 days and was only the size of a basketball. Stories have floated around the pacific northwest for years about old tubers being as large as an adult male human body. Which I now believe, having dug up this one young tuber. Cheers, Kathleen