Onions and garlic are staples in almost every global cuisine, providing a foundational flavor base for countless dishes. Despite their distinct tastes and appearances—one a single large bulb and the other a cluster of cloves—their botanical relationship is much closer than many people realize. Understanding their shared scientific classification reveals the common traits that give these vegetables their unique culinary power.
The Taxonomic Home of Onions and Garlic
Both the onion and garlic belong to the large plant genus Allium, which is the scientific name for this group of monocotyledonous flowering plants. This genus is currently classified within the family Amaryllidaceae, specifically as a member of the subfamily Allioideae. The Amaryllidaceae family also includes plants such as daffodils and amaryllis.
Plant taxonomy is a dynamic field, and the classification of this group has changed over time. Historically, onions and garlic were often placed in the family Liliaceae (the lily family). Modern molecular analysis resulted in the current placement of the genus Allium into the larger family Amaryllidaceae, with the former family Alliaceae now serving as the subfamily Allioideae.
Defining Characteristics of the Allium Genus
The defining characteristics of the Allium genus are both physical and chemical, distinguishing them from other plant groups. All members are herbaceous perennial plants that typically grow from a true bulb, a specialized underground storage structure. This bulb is typically enclosed in a membranous, papery outer layer, helping the species survive through winter or dry periods.
The most recognizable trait shared across the genus is the distinct, pungent odor and flavor. This characteristic smell is caused by the presence of unique sulfur compounds, such as cysteine sulfoxides, which are released when the plant tissue is cut or crushed. When exposed to air, these compounds convert into volatile sulfur chemicals, like allicin, responsible for garlic’s potent aroma.
Another shared botanical trait is their specific flower structure. The flowers grow in a dense, spherical cluster, known as an umbel, at the top of a leafless stalk. Many species can also reproduce asexually by producing tiny secondary bulbs, called bulbils, sometimes directly within the flower cluster.
Other Edible Members of the Family
Beyond the common onion and garlic, the Allium genus contains many other economically important species used in cooking worldwide. Shallots (Allium cepa Aggregatum Group) are closely related to the onion but grow in clusters of smaller bulbs. They offer a milder, more delicate flavor than the common onion.
Leeks (Allium ampeloprasum) are grown for their long, thick, white stems and have a much milder, sweeter flavor. Chives (Allium schoenoprasum) are the smallest members of the group, valued for their slender, hollow green leaves used as a fresh herb or garnish. Scallions, also known as green onions, are typically young common onions or Welsh onions (Allium fistulosum) harvested before the bulb fully develops.