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The calligrapher fly, Toxomerus marginatus, is a generalist, here it’s pollinating a catalpa flower (Trinity Campus, UVM)

The “reason” for a flower

Generally speaking, animal-pollinated (zoophilous) flowers are more effective at effecting the transfer of pollen than wind (anemophilous) because they rely on animals to take pollen directly to another – and hopefully – receptive flower rather than relying on chance. But with all mutualisms, there’s a trade off, and flowers must produce enough nectar to entice pollinators into spending enough time buzzing around their flower to pick up stray pollen grains. They then walk, fly, or buzz directly to another flower, often of the same species, bringing pollen right from plant A to plant B (interestingly, most plants have individual flowers or entire individuals within the population that cheat the system and are entirely nectarless). To advertise that nectar is present and ripe for the taking, flowers are often bright, showy, and/or fragrant.

The stinky exceptions

Pollination Syndromes

But not all pollinators are in search of the same sights and smells. They don’t even all see the world in the same colors or search at the same time of day (or night). Because there’s so much variability in pollinators, a flower can be particularly focused on exploiting a specific set of pollinators, making it all the more likely that the pollinator’s next visit will be to a flower of the same species. There’s a rough sketch of patterns that ecologists have pieced together to make predictions about the animal species who pollinates a flower based on the appearance of the flower. And indeed, these patterns, or pollination syndromes, are quite helpful when getting to know the flowers in your backyard (check out this video on Darwin’s greatest prediction: link).

Wild ginger flowers grow in the “understory” below the plants leaves and are pollinated by low flying gnats and beetles.

The smellier side of pollination syndromes

As in the description above, pollination syndromes mostly describe mutualistic relationships (a form of symbiosis where both species benefit from the relationship). But not all flowers are so magnanimously sweet. Some, in fact, are quite stinky. Literally and metaphorically. These stinky plants, with aptonyms like corpse flower, stinking Benjamin, and skunk cabbage, emit scent molecules that mimic molecules, with names like putrescine and cadaverine, which are emitted by decomposing carcasses and scat. They fool their pollinators (when the pollinators are flies, they’re called sapromyophiles) into thinking that there’s a fetid meal at the end of the foul road. The frustrated flies, ants, beetles, etc. frantically search the flesh- or poop-colored flowers for food before ultimately giving up and moving onto the next flower. This exploitative symbiotic relationship amounts to a form of parasitism.

Close up of the wild ginger flowers

So what do the flowers look like?
Fortunately, you can tell which flowers smell without actually smelling them! Because they’re mimicking rotting flesh, they not only have the smell, but they have the puce color of rotting flesh. And, conveniently, most of these flowers are among the first flowers to emerge in the northeast. For most of the winter, flying insects are dormant (snow dipterans are often an exception). Because insects are dormant and bacterial decomposition slows significantly, not much decomposition happens during the winter. The first warm temperatures of spring melt the snow and expose mammal carcasses. A small field of skunk cabbage looks somewhat similar to a field of small dead mammals poking up from the snow. Hungry insects emerge in search of rotting corpses and are often fooled by these botanical mimics. And again, because they’re “tricking” the insects, they don’t need to provide any nectar. A pretty neat trick.

Skunk cabbage emits chemicals reminescent of those found in scat (note the blue bottle fly, Calliphora vomitoria, on the right)

More on the topic

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