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Humans have delighted in the scents of flowering plants since the beginning of time, but flowers don鈥檛 smell good to please us. It鈥檚 insect pollinators they鈥檙e trying to bewitch. The very survival of flowering plants depends on it.

It鈥檚 all about reproduction.

Flowers use a combination of visual cues, including vibrant colors, distinct shapes, invisible ultraviolet patterns and structural 鈥渞unways鈥� or 鈥渓anding pads,鈥� to guide pollinators to a pollen and nectar reward.

While visual cues help pollinators find flowers, thousands of plant species evolved to produce scents, indicating that visual cues were not always enough to get the job done.

No two plants produce the exact same scent, yet pollinators can discriminate among subtle differences in this vast array of aromas. Scientists have cataloged 1,700 different scent compounds produced by flowers. Some flower fragrances are composed of more than 200 different compounds.

Plants that rely on pollination by bees or butterflies have relatively sweet scents, and their flowers emit the highest scent levels during the daytime. Plants pollinated by moths or bats produce the highest scent levels at night, when those animals are actively seeking food sources and visual cues are hidden in the darkness.

Many flowering plants are 鈥済eneralists,鈥� emitting scents that appeal to a wide variety of pollinators. On the other hand, Darwin鈥檚 orchid emits a distinct fragrance that attracts only the giant sphinx moth, which evolved a remarkably long proboscis to reach this particular flower鈥檚 nectar.

Flowers walk a fine line in scent production. On one hand, enough scent must be produced to lure pollinators to fertilize their flowers. On the other, they don鈥檛 want to overdo it and waste the valuable, limited energy reserves that scent production requires.

To be most efficient, flowering plants time their scent production to coincide with when the maximum amount of pollen is available in their flowers. Mature flowers release more intense scents than young flowers but later pull back and reduce the quantity and quality of their fragrance. This directs pollinators to move on to new flowers, increasing the chances of successful reproduction.

The Titan arum (Amorphophallus titanum) is an endangered plant native to the rainforests of Sumatra, Indonesia. Like other flowering plants, the Titan arum uses scent to attract pollinators when it鈥檚 ready to reproduce. Calling this arum a 鈥渄rama queen鈥� is an understatement.

It can take up to 10 years for a Titan arum to produce the largest inflorescence in the plant kingdom, which can reach 12 feet in height. A leaf is produced each year from the corm, which absorbs and stores energy from sunlight.

When enough energy has been stored to produce a flower bud, the Titan arum will attempt to reproduce. At bloom time, the arum鈥檚 corm can be larger than a beach ball and weigh more than 200 pounds.

If all systems are 鈥済o,鈥� the spiky spadix emerges from the ruffly spathe at a rate of 4 to 6 inches per day. A spadix is a botanical cluster of many tiny, tightly packed flowers arranged on a thickened, fleshy central stem. It is often enveloped by a hooded bract called a spathe.

About two weeks into the process, growth slows and the spathe begins to open. Botanic gardens around the world with a Titan arum in their collections have livestreamed this event to thousands of plant aficionados eager to witness something truly extraordinary.

Unlike most flowering plants, the arum has enough stored energy to pulse out its scent in one big burst. It鈥檚 not a smell you might expect.

Carrion beetles and flesh flies are the Titan arum鈥檚 natural pollinators. To get their attention, the arum produces a scent that has been described as decaying, rancid, rotten flesh wrapped in a dirty diaper. It鈥檚 enough to attract insects from an acre away.

Drawn by the scent of something dead on which to lay their eggs, the beetles and flies deposit pollen carried on their backs and bodies from the last flower or inflorescence they visited, completing the act of pollination in a single evening.

Next time you bury your nose in a big bouquet of florist roses and smell, quite frankly, not much, blame commercial rose breeders. Scent genes were often sacrificed in the drive to produce longer-lasting stems, vibrant colors and sturdy petals that survive long-distance shipping.

But the next time you bury your nose in a bouquet of homegrown lilacs, lilies or sweet peas, thank the natural co-evolution of flowering plants and insect pollinators for the magnificent achievement of those gorgeous scents.