The common garden query, “Is an iris a lily?” arises frequently because both are popular, showy perennial flowers found in many gardens. Both the Iris and the Lily are known for their vibrant colors and distinctive shapes. Despite their superficial similarities, the definitive answer is no: they belong to entirely separate plant families. This separation is based on distinct biological differences in classification and physical structure.
The Definitive Answer: Taxonomic Classification
In the world of botany, plants are organized into a hierarchy to reflect their evolutionary relationships and shared characteristics. This system ensures clarity, avoiding the confusion that can arise from common names. Both Iris and Lily are classified as monocots, meaning they are flowering plants that produce a single seed leaf upon germination. They also share the same order, Liliales (or sometimes Asparagales), a broad grouping of lily-like plants. The separation occurs at the family level, a much more specific grouping based on detailed structural and genetic traits. The Iris belongs to the family Iridaceae, which includes familiar garden plants like the Gladiolus and Crocus. The Lily belongs to the family Liliaceae, home to the true lilies (Lilium species).
Key Differences in Physical Structure
Flower Structure
The most apparent distinctions between the two can be seen in their flowers. The Iris flower features six petal-like segments arranged in two distinct groups: three upright inner segments called “standards” and three outer, often downward-curving segments known as “falls.” The Iris has only three stamens, which are hidden beneath the style branches. Conversely, the Lily flower typically displays six nearly identical petal-like structures (three true petals and three sepals) arranged symmetrically. A true Lily flower contains six prominent, easily visible stamens, double the number found in the Iris.
Leaf Morphology
Leaf morphology also offers a clear way to tell the plants apart in the garden. Iris leaves are typically flattened, sword-like, and grow in a fan shape from the base of the plant, with their bases overlapping in a two-ranked arrangement. In contrast, Lily plants grow a central, unbranched stem. Their leaves are usually distributed along the length of this stalk, often in whorls or spirals.
Underground Structures
The underground structures used for survival and propagation are fundamentally different. Most Irises grow from a fleshy, horizontal stem known as a rhizome, which stores nutrients and usually sits near or slightly above the soil surface. Lilies, however, grow from a true bulb, which is an oval-to-round structure made up of fleshy, concentric scales. These bulbs need to be planted deeper in the soil to thrive.
Why the Confusion Exists
The persistent confusion between the Iris and the Lily stems from several shared characteristics that lead people to group them together. Both plants are herbaceous perennials that grow from underground storage organs and produce large, showy flowers, making them popular ornamental additions to gardens. They also share a high-level classification as monocots, exhibiting flower parts in multiples of three and possessing leaves with parallel venation. Historical factors also contribute to the mix-up, particularly the famous fleur-de-lis, the stylized emblem historically associated with the French monarchy. Although the French term lis means “lily,” the design of the fleur-de-lis is widely believed to be based on the structure of a stylized Iris flower, specifically the yellow flag iris.