The Titillating Sex Life of Orchids

Flowers are all about sex. If they look good and smell good, it’s not to please us humans, but to better seduce their pollinators, because most need cross pollination (transfer of pollen from the flower of one plant to the flower of another of the same species) in order to reproduce. And orchids are the masters of sex when it comes to the world of plants.

How Plants “Do It”

Many plants (conifers, oaks, grasses, etc.) produce extra-light pollen in copious quantities then liberate it massively into the air so it will be carried away by the wind. They do so in the hopes (yes, I’m going to go a bit anthropomorphic in this blog; it just makes the explanations so much simpler!) that a single pollen grain will accidentally land on a receptive flower of the right species. Wind pollination does work (otherwise, the species that do it would have gone extinct), but what a waste of resources! Sometimes the entire landscape is covered with a thin layer of pollen that will never serve the plant in any way.

Other plants use a more reliable pollinator than the wind—usually an insect, although occasionally a bird (a hummingbird, for example) or a mammal—to carry their pollen from one flower to another. Many essentially offer an open bar: they give as a reward a generous amount of nectar and pollen and are none too picky when it comes to their suitors. Think of the common oxeye daisy, Leucanthemum vulgare, found in fields everywhere. It gives off a subtle, sugary, generic odor that attracts a wide range of insects and its florets just drip with nectar. It likewise produces more pollen that it needs so pollen-eating insects can have their share. The daisy can be pollinated by bees, flies, butterflies, beetles or wasps of many different species.

Scientists have a way of spelling things out quite bluntly and call such blooms promiscuous flowers. (If they hadn’t said it, I would have!) Such plants are counting on the likelihood that one of their many pollen-laden visitors will eventually land on a plant of the same species and that some of the pollen that stuck to its body as it fed will come free and ensure fertilization. That’s still a lot of nibbles and booze (oops, I mean pollen and nectar) to give away, but at least the investment is worthwhile if they achieve pollination.

Other flowers are very specific … and orchids are often in this group. Pollinator-specific flowers come in a distinct color or form, have barriers to keep unwanted pollinators out or a scent that is only appreciated by one specific pollinator or at least a limited number of pollinators, thus forming a specific plant-pollinator interaction. A good example among non-orchids is the yucca moth (Tegeticula sp.), which pollinates only yuccas (Yucca sp.). The plant absolutely needs the pollinator and the pollinator can’t get along without the plant. Such plants don’t need to produce as much pollen and certainly not as much nectar as promiscuous flowers … but they usually do have to curry the favor of their pollinators by rewarding them in some way: pollen, nectar, oils, housing, etc.

Orchids, though, are not as charitable as most plants. Although their heavy pollen can’t be carried by the wind and they are almost always pollinated by insects (more rarely by mammals or birds), they are very stingy with their pollen. They don’t produce “quantities” of pollen, only two pollinia or pollen masses (singular: pollinium) per flower. And most are not particularly generous with their nectar either. Indeed, many produce no nectar at all.

Obviously, it’s vital for a flower with only two pollinia that the insect that picks up its ever-so-rare pollen deposits them on another orchid of the just right species. Thus, orchids will go to almost any length to please their specific pollinator, using clever combinations of colors, scents, shapes and textures to better seduce it … but many still don’t feed it!

Deceptive Flowers

The way orchids get away with “offeriing the product, but not delivering the goods” is by mimicry. They try to replicate things their pollinator will find attractive: flowers, fellow insects … even rotting meat! They can do this by smell, taste, appearance, texture, etc. Their pollinator visits them expecting one thing, but gets … nothing in return. But it leaves with orchid pollinia glued to its body.

One estimate suggests that of the 20,000 species of orchids, about 8,000 are so-called “deceptive flowers”: they claim to offer something interesting to a pollinator, but don’t deliver. Orchids are not the only deceptive flowers, but they are by far the best at floral trickery.

Let’s look at a few examples:

Seducing the Orchid Bee

The bee orchid (Ophrys apifera) is a terrestrial European orchid, also called (I didn’t invent this!) the prostitute orchid. It sets out to seduce a male bee of an appropriate species (different solitary bees in the genera Tetralonia and Eucera). To do so, the bee orchid starts by producing a flower that is physically quite similar to the female of the solitary bee. It has the same color (from a bee’s point of view; we don’t see colors the way they do), is the same size and even offers a similar shaggy texture.

But the coup de grâce is the perfume: the flower releases a pheromone (sex hormone) very similar to that of the female bee, but not quite the same. Tantalizingly different, you might say. Enough so that, if the male bee has to choose between the orchid and a female of his species, he often chooses the orchid!

When he lands and tries to copulate with the flower, his movements release the flower’s pollinia that end up literally glued to his head. Frustrated by the flower’s lackluster response, though, he leaves.

Bees may not be very intelligent, but they do learn. As a result, he’ll avoid the next few bee orchid flowers he encounters, remembering the disastrous results of his initial flirtation. But the further away he gets from the original flower, the more his memory fades and soon enough, he’s ready to try again. By now, though, he’s at a considerable distance from the original plant and this ensures that the cross-pollination that occurs will be between plants that are genetically distinct, thus avoiding any consanguinity. Just what the orchid wants!

When he lands on the new flower, the pollinia, if he’s wearing any, get caught in structures in the flower and are literally ripped from his head, then replaced by new ones.

Let’s hope he eventually finds a sweetheart of his own species before he dies of exhaustion!

The bee orchid is hardly an exception. Many orchids mimic the scent of female insects and induce the pseudo-copulation of males for their own reproductive purposes, but few mimic the appearance of the female quite as well as the bee orchid.

A Swarm of Pseudo-Bees

Some species of Oncidium in South and Central America have flowers that subtly mimic the appearance of local bees (genus Centris), but it’s not for the purpose of sexually attracting them. The small flowers are grouped in large numbers on arching stems that move in the slightest breeze, even to the point of seeming to shake.

Male Centris bees are very territorial by nature, and when they see what seems to be a swarm of dancing bees invading their space, they go on the attack, repeatedly dive-bombing the flowers … and when they do, they pick up pollinia by accident. After the exhausting but fruitless attack, they pull back, then discover another “flowery swarm” elsewhere, and attack that too, dropping off pollinia from the first orchid, thus ensuring fertilization, and picking up fresh pollinia. And before they learn better (and they will), this can happen four or five times, leaving the orchids pregnant and happy and the bees confused and frustrated.

Lady’s Slippers

Deceptive orchids aren’t limited strictly to the tropics. The beautiful lady’s slipper (Cypripedium spp.), found, in one form or another, throughout much of the Northern Hemisphere, even in the boreal forest … is definitely on the list of deceptive flowers. In other words, she really isn’t much of a lady!

Its lip, a mutated petal in the shape of a pouch, gives off a honeyed smell that implies an abundant supply of nectar. The insect (a fly, bumblebee or solitary bee, depending on the species of lady slipper: each has its own favorite) lands on the lip looking for the promised nectar. It wanders towards the greatest intensity of scent … to discover itself on the smooth inner surface of the lip. Thus, it slips to the bottom of the pouch where the sweet scent is strongest, figuring it has hit the jackpot, but no, there is no nectar at all. Worse, when it tries to leave, there are downward inclined hairs that prevent it from going back the way it came. The insect is now a prisoner.

Eventually, it discovers an opening at the bottom of the flower and tries to wriggle its way out. In doing so, it drops off any pollinia it was carrying from a previous lady slipper encounter, thus ensuring pollination, but the exit hole is so arranged that, when it does it free, new pollinia are automatically glued to it.

The lady’s slipper orchid is far from the only orchid to use this technique. It’s a fairly common ploy among deceptive orchids.

Stinky Blooms

The gigantic orchid Bulbophyllum phalaenopsis will surely never win any beauty contest. It has to have just about the ugliest flower of any orchid.

Its 15 to 20 reddish-purple flowers look like rotten meat and swarm with fleshy projections said to look like wriggly maggots. In addition, it emits a truly nauseating odor, one said to replicate the stench of a thousand dead elephants rotting in the sun. It does so to attract a female carrion fly looking for a place to lay her eggs. (This is called “brood site deception.”) As she does so, she inadvertently picks up the flower’s pollinia, then carries them off to another flower. When the fly’s eggs hatch, they simply die: there’s nothing there they can actually feed on.

Again, Bulbophyllum phalaenopsis is not alone. Many orchids, including the those in the foreboding-sounding Dracula genus, likewise attract carrions flies with an odor that seems unbearable to our nostrils, yet so enticing to flies!

Flower Mimics

Not all orchid flowers mimic female insects, marauding bees or dead elephants. Many disguise themselves as other flowers.

When an abundant plant has found the key to success with pollinators, it’s far from uncommon for a local orchid to learn to imitate it to take advantage of its pollinators.

In South and Central America, for example, there is a milkweed (Asclepias curassavica) and a lantana (Lantana camara) both of whose flowers share the same color combination (orange with a yellow center) and also the same pollinators—notably specific species of wasps and butterflies—and the two produce abundant nectar to ensure their favorite pollen carriers visit faithfully and thus transfer their pollen. However, a few species of Epidendrum—including E. radicans—have learned to mimic them by producing flowers of exactly the same colors … but with the difference that these orchids offer no reward whatsoever. The insects visit, pick up their orchid’s pollinia, and leave hungry and confused, the promised nectar simply being absent.

Again, there are hundreds of other orchids that mimic other flowers so they can “steal” their pollinators. It’s just something orchids do!

50 Shades of Orchid Sex

Obviously, there are many other deviations in the twisted sex life of orchids that I could have told you about:

• A Catasetum that shoots its pollinia onto the head of its pollinator with such force that it is sometimes knocked unconscious or even killed by the experience;
• Darwin’s orchid (Angraecum sesquipedale) so badly wants to preserve its precious nectar from nectar thieves that it stores it at the bottom of a one foot (30 cm) spur so that only its exclusive pollinator, a moth called Xanthopan morgani praedicta, whose probiscus is just long enough, can reach it;
• Holcoglossum amesianum which, if its preferred pollinator doesn’t show up, self-pollinates in such a very physical way that I wouldn’t dare to describe it in a blog that could be easily read by children;
• And many more!

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Decidedly, orchids are the vixens of the plant world … and they seduce humans too! After all, what do we do when so they shamelessly offer themselves to all and sundry with their sultry flowers, but take them from the wild and grow them in our homes and gardens!

Sex sells: it always has!