Here are trees and shrubs whose flowers or other parts produce odors that many people describe as resembling semen or a similar unpleasant, musky smell. The chemistry behind these odors is well understood — the primary culprit in most cases is a compound called trimethylamine or related organic amines such as putrescine and spermidine, which are naturally produced in plant tissues and serve ecological functions in attracting specific pollinators such as flies and beetles that are drawn to fetid, organic smells.
Trees And Shrubs With Unpleasant, Musky Smell
Callery Pear (Pyrus calleryana — wild and other cultivars)
While the Bradford pear was covered above as the most notorious cultivar, the entire Callery pear species deserves recognition as a group for its universally offensive floral scent. All cultivars of Pyrus calleryana — including ‘Aristocrat,’ ‘Cleveland Select,’ ‘Chanticleer,’ and ‘Redspire,’ which were developed as alternatives to the structurally weak Bradford — share the same fundamental floral chemistry and produce the same trimethylamine-laden odor during their spring flowering period. ‘Chanticleer’ in particular has been widely promoted as an improved Callery pear and planted extensively as a street tree across Europe and North America — making the annual spring flowering of urban streets lined with this tree a sensory challenge for pedestrians.
The intensity of the smell varies somewhat between cultivars and between individual trees, and some people are less sensitive to trimethylamine than others, but the consensus among those who notice it is consistent and unmistakable. The invasiveness of the species compounds the environmental objections to its continued widespread planting.
Bradford Pear (Pyrus calleryana ‘Bradford’)
The Bradford pear is perhaps the most notorious of all offensively scented flowering trees, and its smell in full bloom is the subject of widespread complaint across suburban North America every spring. Native to China and Korea, it was introduced to the United States in the 1960s as an ornamental street and garden tree and was planted in enormous quantities throughout the 1970s, 80s, and 90s for its neat, symmetrical shape, glossy foliage, brilliant autumn color, and spectacular clouds of white spring blossom.
The problem is that those white flowers produce trimethylamine and related amines in quantities sufficient to create a pervasive, unmistakable odor that most people describe as resembling semen, rotting fish, or a combination of both. The smell is most intense on warm, still days when the volatile compounds accumulate around the tree rather than dispersing on the breeze.
Adding to its problems, the Bradford pear has proven structurally weak — its tight branch angles cause limbs to split in storms — and deeply invasive across eastern North America, escaping gardens and colonizing roadsides and woodland edges at an alarming rate. Several American states have moved to ban its sale and planting entirely.
Ginkgo (Ginkgo biloba — female trees)
The ginkgo is one of the most ancient trees on Earth, a living fossil with a lineage stretching back 270 million years, and in most respects it is a magnificent, pollution-tolerant, disease-resistant, and extraordinarily long-lived ornamental tree. The problem lies exclusively with the female trees, which produce fleshy, plum-like seeds containing butyric acid — the same compound responsible for the smell of rancid butter and vomit — along with other short-chain fatty acids including the amines that produce a semen-like odor.
When the seeds ripen and fall to the ground in autumn and begin to decompose underfoot, the smell can be truly overwhelming — a combination of vomit, rancid cheese, and fetid organic matter that makes walking beneath a mature female ginkgo an unpleasant experience. For this reason, most horticulturalists and urban foresters strongly recommend planting only male ginkgo trees, and numerous male cultivars are available. The seeds themselves, called ginkgo nuts, are considered a delicacy across East Asia when properly cleaned and cooked, and the smell is entirely confined to the fleshy outer coating.
Chestnut (Castanea species — particularly Castanea sativa)
The sweet chestnut is a magnificent, large deciduous tree native to southern Europe and western Asia, producing one of the most valued edible nuts in the world and timber of exceptional quality — and also producing one of the most powerfully and distinctively unpleasant floral odors of any temperate tree. The long, creamy-yellow catkins that appear in midsummer contain both male and female flowers and release their pollen accompanied by a heavy, unmistakable odor that has been widely described as resembling semen, combined with overtones of ammonia and overripe cheese.
The smell is produced by trimethylamine and related compounds and is most intense in hot, still weather when the catkins are releasing maximum pollen. The function of this odor is to attract flies and other insects that are drawn to fetid, organic smells for pollination — a strategy called sapromyiophily. Despite the offensive floral scent, the sweet chestnut is otherwise an outstanding tree of immense ecological and economic value, and the smell is relatively short-lived, lasting only for the few weeks of peak flowering in mid to late summer.
Black Locust (Robinia pseudoacacia)
The black locust is a large, fast-growing deciduous tree native to the Appalachian Mountains and Ozark Plateau of the eastern United States, now naturalized and in many regions invasive across Europe, Asia, and other parts of North America. In late spring it produces spectacular, pendulous clusters of white, pea-like flowers — structurally beautiful and intensely fragrant with a sweet, almost vanilla-like perfume that is genuinely pleasant to most people at low concentrations.
However, at close range and in large quantities — particularly when standing beneath a tree in full bloom on a warm, humid day — the fragrance develops heavier, more complex undertones that many people describe as having a distinctly semen-like or musky animal quality beneath the sweetness.
The floral compounds responsible include indole — a nitrogen-containing organic compound produced by many flowers to attract pollinators but which at higher concentrations produces a fetid, fecal, or semen-like quality. Black locust honey, produced by bees working the flowers, is considered one of the finest and most delicately flavored honeys in Europe, suggesting that the volatile compounds disperse and transform significantly between flower and honey.
Elderflower (Sambucus nigra)
The elder is a large, fast-growing deciduous shrub or small tree native to Europe, western Asia, and North Africa, producing flat-topped clusters of tiny cream-white flowers in early summer that are used across Europe to make elderflower cordial, elderflower champagne, fritters, and a range of other culinary preparations valued for their delicate, muscat-grape-like fragrance.
However, the flowers of elderflower have a notably dual character — at a distance and in small quantities the scent is undeniably attractive, floral, and sweet, but at close range and in large quantities the same flowers produce unmistakable overtones of a semen-like, musky, slightly fetid quality that many people find overpowering and unpleasant.
This duality is chemically explained by the presence of trimethylamine alongside the more pleasant floral volatiles — the pleasant scent compounds dominate at low concentrations and distances, while the amines become more apparent at close range. The leaves, bark, and unripe berries of elder are toxic, and the crushed leaves produce an entirely different, deeply unpleasant smell described as mouse-like and fetid.
Pyracantha (Pyracantha species — Firethorn)
Pyracantha, commonly known as firethorn, is a group of evergreen thorny shrubs native to southeastern Europe and Asia, enormously popular in gardens and landscapes worldwide for their spectacular displays of orange, red, or yellow berries in autumn and winter, and for their dense, thorny habit that makes them excellent security hedges and wildlife shrubs.
In late spring and early summer they produce masses of small, white, five-petaled flowers in dense clusters across the entire surface of the shrub — a flowering display that is visually attractive and covers the plant so completely that the foliage is almost obscured. The smell of these flowers, however, is widely reported as distinctly unpleasant — variously described as fishy, musty, and with an unmistakable semen-like quality produced by trimethylamine and related amine compounds.
The function, as with other amine-scented flowers, is to attract flies as pollinators rather than bees or butterflies. The smell is relatively short-lived — lasting only for the two to three weeks of peak flowering — and the extraordinary berry display that follows in autumn is considered by most gardeners to be ample compensation for the brief olfactory challenge of the flowering period.
Hawthorn (Crataegus monogyna and related species)
The hawthorn is one of the most deeply embedded trees in the folklore, hedgerow ecology, and rural landscape of the British Isles and Europe — a thorny, long-lived small tree or shrub that has been used for stock-proof hedging, wildlife habitat, and traditional medicine for thousands of years. In May it produces its famous “May blossom” — clouds of small, white or pale pink five-petaled flowers so abundant that the entire hedge or tree appears dusted with snow, and the countryside lanes of rural Britain and Ireland are briefly transformed into corridors of white.
The smell of hawthorn blossom is one of the most polarizing of any native tree — some people find it sweetly floral and evocative of the countryside in spring, while a large proportion of the population finds it distinctly and unmistakably reminiscent of semen, rotting meat, or a combination of both. The chemical explanation lies in the presence of trimethylamine alongside dimethylamine in the flowers — the same compounds produced in decaying animal tissue, which attract carrion flies as pollinators.
There is a long tradition in British folklore of considering hawthorn blossom unlucky to bring indoors, and while this superstition is often attributed to the association of the smell with death and plague — the flowers were said to smell of the Great Plague of London — the chemical basis for the unpleasant association is entirely real. The berries, called haws, are entirely odorless and are an invaluable food source for birds through autumn and winter.
Horse Chestnut (Aesculus hippocastanum)
The horse chestnut is a large, majestic deciduous tree native to a small area of the Balkans — the Pindus Mountains of Albania and Greece — but planted so extensively across Europe and North America since the 17th century that it has become one of the most familiar and beloved trees of temperate parks, avenues, and village greens. In late spring it produces its spectacular “candles” — large, upright conical panicles of white flowers marked with yellow and pink spots, standing erect above the magnificent palmate leaves like candelabra on a grand scale.
At a distance these flower spikes are purely beautiful, and the tree in full bloom is genuinely one of the finest sights of the late spring landscape. At close range, however, the flowers produce a heavy, complex scent that includes distinctly unpleasant overtones widely described as musky, stale, and with an unmistakable semen-like quality that becomes more pronounced on warm, humid days when volatile compounds accumulate in the still air beneath the canopy.
The smell is produced by indole and trimethylamine compounds alongside the more pleasant floral volatiles, and its function is to attract a broad range of insect pollinators including flies that respond to the fetid components of the scent blend. Despite this olfactory complexity, the horse chestnut remains enormously popular — its conkers beloved by children, its autumn color attractive, and its overall presence in the landscape majestic and irreplaceable.
Lily of the Valley Tree (Clethra alnifolia — Summersweet)
The summersweet, or sweet pepperbush, is a deciduous shrub native to the eastern coastal plain of North America, from Maine south to Florida, typically found growing in moist, acidic soils along stream banks, pond margins, and in coastal plain wetlands. In midsummer it produces upright spikes of small, white or pale pink flowers that release a powerful, complex fragrance described by many as spicy, sweet, and clove-like at a distance — genuinely pleasant and one of the reasons the shrub is popular in native plant gardens and naturalistic landscapes.
However, at close range and particularly on still, humid summer days when the volatile compounds concentrate around the shrub, the fragrance develops a distinctly heavy, musky, semen-like undertone that many people find surprising given the initially pleasant impression of the scent from a distance. This olfactory duality — attractive at a distance, challenging at close quarters — is characteristic of many amine-containing floral scents, where the balance between pleasant aromatic compounds and the heavier trimethylamine components shifts depending on concentration and proximity.
Despite this characteristic, summersweet remains an excellent native shrub for moist, shaded situations, providing summer flowers when few other shrubs are blooming, outstanding fragrance in the garden at reasonable distances, brilliant yellow autumn color, and persistent seed capsules that provide winter interest and food for birds.