Yacon is a relative of the sunflower and Jerusalem artichoke that produces huge storage tubers that are typically eaten raw as a fruit, but can also be cooked or reduced to a sweet syrup like molasses. They are crisp and juicy, slightly sweet, with a flavor that is often described as a mixture of things like apple, pear, and celery. It sounds a little strange, but it seems to be uncontroversially tasty. Currently the subject of a lot of health claims, which are probably overblown. Yacon is a pretty easy and forgiving crop. It likes plenty of water, but it is not bothered by the heat of continental summers, so can be grown in North America anywhere there is a frost-free season of at least seven months.
Yacon is generally planted from pieces of the crown (rhizome), which is how varieties are maintained. Yacon can also be grown from seed, which is primarily used by breeders to produce new varieties. If you are in doubt about whether to buy rhizome or seeds, you probably want rhizome.