The answer is a tuber.
Tuber is a fleshy end of a stem enlarged for food storage and asexual reproduction.It provides nutrients for the next season regrowth.It is specialized for asexual reproduction, which involves the formation of offsprings without gamete fusion.Potato is a stem tuber, for example. In one growing season, the tuber is produced and used to perennate the plant. In the autumn, when the plant structure above-ground dies, the tuber survives over the winter underground. When spring comes, tuber regenerates new shoots thanks to nutrients stored.