No, lilies and daylilies are not the same plant and belong to completely different botanical families, which is the most crucial difference from a plant science perspective. True lilies are members of the genus Lilium within the family Liliaceae. This genus includes well-known species like the Asiatic, Oriental, and Easter lilies. In contrast, daylilies belong to the genus Hemerocallis, which is part of the family Asphodelaceae. This separate taxonomic classification highlights that they are distinct genera with different evolutionary histories and genetic makeups, despite the confusing similarity in their common names.
The physical structures of these plants provide clear identifiers for gardeners. True lilies (Lilium) grow from a bulb, which is a modified stem with scales that store nutrients. Their stems are singular, upright, and leafy, producing flowers along the stalk. The leaves are typically arranged in whorls or spirals around the stem. Daylilies (Hemerocallis), however, grow from a mass of fleshy, thickened roots called a tuberous root system or clumps. Their leaves are long, grass-like, and arching, growing directly from the crown of the plant in a clumping habit. The flower scapes (stems) of daylilies are leafless and rise above the foliage clump.
The flowers, while sometimes similar in shape to the untrained eye, have distinct anatomical differences. A true lily flower has six stamens and a single pistil. The flowers can face upward, downward, or outward and are complete, containing both male and female reproductive structures. Most significantly, a true lily flower can last for a week or more on the plant. A daylily flower, as its name implies, typically lasts for only one day, opening in the morning and withering by the evening. Each flower has six stamens and one pistil, but it is a key identifier that each scape produces multiple flower buds that open successively over a period of weeks.
The growth and reproductive strategies of these plants differ significantly. True lilies are primarily propagated through the division of their bulbs and the planting of bulb scales or bulbils. They are classic perennial bulbs. Daylilies are propagated by dividing their fibrous crown and tuberous roots. They form dense clumps that can be easily split every few years. This difference in root structure also affects their planting depth; lily bulbs are planted deeply, while daylily crowns are planted just at or below the soil surface.
A critical difference for gardeners with pets is the matter of toxicity. Members of the Lilium genus (true lilies) are highly toxic to cats. Ingesting any part of the plant, including pollen, can cause acute kidney failure and is potentially fatal. Daylilies (Hemerocallis), while also toxic to cats, are reportedly less so than true lilies, but caution is still strongly advised. Conversely, some daylilies are edible for humans, with their buds and flowers used in some culinary traditions, whereas true lilies are not considered edible and can cause illness.
