The distinct, sometimes unpleasant odor associated with certain lily varieties is a known biological characteristic, not a sign of decay. For many people, the heavy floral scent can take on a foul quality, often described as smelling like ammonia or urine. This observation is rooted in the plant’s chemistry, where specific airborne volatile compounds are produced as part of its natural metabolism. These compounds trigger receptors in the human nose, leading to the perception of a chemical scent similar to nitrogenous waste. The presence and intensity of this aroma serve a precise, adaptive function determined by the plant’s genetics.
Volatile Compounds That Mimic Ammonia
The characteristic urine-like smell is caused by the emission of Volatile Organic Compounds (VOCs), specifically nitrogen-containing molecules known as amines. One of the main culprits is trimethylamine (TMA), a compound produced by the biological breakdown of nitrogenous matter. In high concentrations, trimethylamine is known for its pungent odor, often described as fishy, rotten, or distinctly ammonia-like. The human nose is exceptionally sensitive to these nitrogenous compounds, which are also naturally present in trace amounts in urine, contributing to the perceived similarity in scent.
Another group of compounds contributing to the foul smell is indoles and their derivatives, like skatole. These compounds are derived from the amino acid tryptophan and are heavily associated with the smell of feces and decaying animal matter. While in trace amounts, indole contributes a sweet, narcotic note to many white flowers like jasmine, in higher concentrations, it rapidly shifts to a heavy, putrid odor. When these amines and indoles are produced by the flower, they act as a chemical mimicry system, designed to attract a very particular group of insects.
The production of these scent molecules is an active metabolic process within the lily’s floral tissue. As the flower matures, its metabolism shifts to produce and release these VOCs. This release is an energy investment, indicating the unpleasant odor is a deliberate biological signal, not a waste product. The ammonia-like scent is simply an overlap between the volatile nitrogenous compounds used by the plant and those found in animal waste.
The Evolutionary Purpose of Foul Scents
The evolutionary reason behind a lily producing a foul scent is tied to a specialized biological strategy known as a pollination syndrome. While many flowers use sweet, fruity, or musky scents to attract bees, butterflies, and moths, the foul-smelling flowers target insects that seek out decaying organic material. This specific type of pollination is called sapromyophily, which translates to “carrion-loving” and attracts flies, fungus gnats, and certain beetles.
The flower’s scent acts as a precise chemical beacon, simulating the odor of a dead animal or droppings. Carrion or dung feeders visit the flower believing they have found a suitable place to lay eggs or feed. As the insect explores, it inadvertently brushes against the anthers and stigma, transferring pollen. This deception ensures the plant’s reproductive success.
For lilies, this foul-scent strategy contrasts sharply with the classic moth-pollination syndrome seen in many sweet-smelling white Lilium species. Flowers adapted for moth pollination, such as the Lilium longiflorum, are typically pale, open at night, and emit sweet fragrances to attract long-tongued hawk moths. The presence of both sweet- and foul-scented varieties within the Lilium genus demonstrates the wide range of evolutionary adaptations plants use to secure a pollinator partner. The foul scent is therefore a highly refined adaptation for attracting specialized, non-traditional pollinators.
Differentiating Scent Profiles Among Lily Species
Not all lilies possess the same scent profile, and the perception of a “urine” smell often depends on the specific species or hybrid. The genus Lilium contains a wide array of scent types, ranging from the richly sweet to the nearly unscented. For instance, the popular Oriental hybrids, such as ‘Stargazer’ and ‘Casa Blanca,’ are known for their powerful, sweet, and spicy perfumes, dominated by compounds like linalool and methyl benzoate. Conversely, most Asiatic lilies are celebrated for their vibrant colors but lack any detectable fragrance, making them a safe choice for those sensitive to strong odors.
The culprits for the foul-smell perception often fall within certain trumpet lilies or are related to the flower’s condition. Some naturally fragrant species, particularly the large-flowered trumpet and Aurelian hybrids, can emit an overwhelming scent perceived as unpleasant by sensitive noses. Furthermore, the pungent smell is often heightened when lilies are kept in a vase indoors, especially as they age or if the water becomes murky. As the floral parts and pollen start to break down, the concentration of naturally occurring volatile amines increases, intensifying the ammonia-like odor.
It is important to note the common confusion with other plants that have a truly putrid odor but are mistakenly called lilies. Aroids, such as the Voodoo Lily (Dracunculus vulgaris) or the infamous Corpse Flower (Amorphophallus titanum), are genetically distinct from true Lilium species but exhibit the foul-scent strategy in its most extreme form. These plants release much higher concentrations of sulfur and nitrogen compounds to mimic carrion, ensuring they attract large numbers of flies for pollination. This scent is far more aggressively unpleasant than the subtle ammonia-like note found in some true lilies.