Asparagus is considered to be a vegetable because of the fact that it does not contain any seeds, does not grow from a flower, and comes from a stem. These are just some of the defining characteristics of vegetables which are used to classify certain foods.
This particular vegetable comes from the Asparagus genus and is considered to be a flowering perennial which means that once planted it continues coming back each season. It is part of the lily family and has edible roots along with flower clusters. Some of its closest cousins include garlic along with onions which are part of the lily family.