Warning: You may not want to read this while you are trying to enjoy your cuppa and a meal.
Stinky plants. What comes to mind? For many, maybe the Titan arum (Amorphophallus titanium) – the plant that produces a giant bloom every 20-40 years. When conservatories have one that's about to bloom, people from all around flock to see the beautiful flower and to experience the truly reeking stench. But you really don't have to travel far to experience plants, trees and shrubs that also smell just plain bad.
A common tree planted along city streets, the Bradford pear (Pyrus calleryana ‘Bradford') displays masses of pretty white springtime flowers that smell like cat urine. Some think the odor is closer to a rotting fish or corpse, an odor shared with the mountain ash tree (Sorbus americana) and the hawthorn tree (Crataegus). The hawthorn's odor was also linked to the plague of the Middle Ages since the tree smelled like the recently dead victims of the disease. Sometimes it's the tree's gender that determines if it is smelly. Decaying “berries” of female Gingko biloba trees smell like rotten eggs, vomit, or rancid butter depending on the nose. For this reason, male Gingko trees are obviously preferred for most landscapes. Male Chinese Trees of Heaven (Ailanthus altissima) produce abundant yellow-green flowers that smell like semen as do male flowers of the Chinese chestnut tree (Castanea mollissima) and Photinia's blossoms.
Some boxwoods, mostly the English variety, smell like cat urine, as do flowers of the Shasta daisy (Leucanthemum × superbum), paperwhite narcissus, and brushed or broken branches of lantana. Skunky odor has been associated with North American Skunk Cabbage, crown Imperial (Fritillaria imperialis), the shrub White Stopper (Eugenia axillaris), and older varieties of Cleome or spider flower. Newer varieties have been bred to be free of that distinction. The smell of decaying flesh is common to the flowers of stinking corpse lily (Rafflesia arnoldii), the foliage of stinking iris (Iris foetidissima), pineapple lily (Eucomis comosa), the flower and foliage of pipevines, and the first 24 hours of bloom of the Voodoo lily (Dracunculus vulgaris).
Some plants have very unique odors. Creeping phlox (Phlox subulata) smells like marijuana. Sea holly flowers (Eryngium maritimum) smell like dog poop. The roots of Valerian smell like dirty socks. The brushed or crushed leaves of Datura smell like rancid peanut butter. Marigold leaves are quite pungent, but, interestingly, when one of the seed companies bred the odor out, gardeners didn't buy it. They wanted the usual, expected odor!
So, what do most of these stinky plants have in common? They all share chemicals/molecules in their makeup with the odor our noses and brains have assigned them. Interestingly, though, the pollinators you may have thought them to have, for example, flies, carrion, or other types of beetles, are not often the case. Xerces Society lists numerous pollinators for each of these smelly characters.
For more information about the smells, odors, and scents, check out Nose Dive A Field Guide to the World's Smells by Harold McGee, Penguin Press, 2020. It gets into the science of these and the rest of our world's smells in the most interesting and entertaining way.