The Monthly Orchid: What do you get when you cross a Coralroot & a wasp?

Answer: Capsules filled with seeds! (Striped Coralroot, Awinch1001)

Welcome back to the The Monthly Orchid, a series about South Dakota's native orchids. This month we again look at Coralroots, specifically the Striped Coralroot, Corallorhiza striata. Coralroots aren't particularly showy, but this one is a bit of an exception. Though the lip petal is small, its stripes are bold. Might they have a purpose? To this, Charles Darwin would reply with an emphatic "Yes!"

Corallorhiza striata; note yellow pollen positioned above base of lip (Freudenstein & Barrett 2026).

Darwin was fascinated by orchid flowers, largely because "the contrivances by which Orchids are fertilised are as varied and almost as perfect as any of the most beautiful adaptations in the animal kingdom." In this diversity, he saw an opportunity to respond to criticism of On the Origin of Species, which he published in 1859.

Just a few years later, Darwin finished another book—The Various Contrivances by which Orchids are Fertilised (1862). In the Introduction, he explained the purpose of his "little treatise" (c. 300 pages):

"Having been blamed for propounding [natural selection] without giving ample facts, for which I had not sufficient space in that work, I wish here to show that I have not spoken without having gone into details."

A myth Darwin intended to debunk was the notion that orchid beauty is "the result of the direct interposition of the Creator" for the pleasure of humans. Wrong! Beautiful orchid flowers are the result of natural selection, and like the vast majority of flowers, they have one purpose—continuation of the species, via sex. 

Why such varied and gorgeous lips? From Kunstformen der Natur, E. Haeckel, 1899.

In last month's post, a Coralroot seed encountered just the right underground fungus, germinated, started to grow, and emerged from the Underworld. We left it surviving on carbon captured by trees and shared (involuntarily) by the fungus. What next? At some point we should see buds, followed by flowers, and then capsules with seeds. Must the fungus help with all this as well? Aside from providing sustenance for growth, the answer is "No". In the case of the Striped Coralroot, however, dependency continues. Now another type of creature will be will be duped.

For most flowing plants (angiosperms), pollination is required to produce seeds. This is what drove evolution of the astonishing diversity in orchid flowers.

South Dakota orchids: Helleborine, Yellow Lady's Slipper, Prairie Fringed Orchid; note the varied contrivances.

With many examples (1), detailed descriptions and lengthy discussion, Darwin was able to argue convincingly that most orchids are designed with insects in mind.

"these contrivances have for their main object the fertilisation of the flowers with pollen brought by insects ... In almost all the species, one of the petals, which is the properly upper one, is larger than the others and stands on the lower side of the flower, where it offers a landing-place for insects, having been carried round by the twisting of the ovarium (2). It is called the lower lip or labellum, and often assumes most singular shapes." (italics mine)

In addition to specialized lips, orchids employ a variety of strategies to lure pollinators (Ackerman et al. 2023; Wikipedia). The most common is attraction by means of reward, e.g., nectar, oil, perfumes. These are given in exchange for pollen transport—arrival from or delivery to another orchid of the same kind. Flower shape, color pattern, and scent are commonly used to attract a specific pollinator, reducing the chance that pollen is wasted on the wrong orchid. 

But many orchids are not so nice. At least a third of the 30,000 known species rely on deception to attract pollinators. Having become highly specialized through natural selection, they are very good at this. Here are some examples.

• An orchid that provides no nourishment has flowers very similar to those of a plant that does. This is feeding deception, the most common type of deceptive pollination. 

• In brood-site deception, an orchid's flowers look like perfect egg-laying sites to the pollinator (see next photo). 

• Even more remarkable is pseudo-antagonism, in which a flower mimics an enemy of the pollinator, invoking an attack during which pollen is transferred!

Cypripedium lichiangense, the Lijiang Cypripedium (Steve Garvie). It offers an appealing (stinky!) but fake brood-site for Ferdinandea cuprea, a hoverfly (Ackerman 2023).

The most fascinating strategy (based on number of studies and websites) appears to be sexual deception, or pseudocopulation. It's the second most common type of deceptive pollination in orchids, documented in at least 22 genera (Ackerman 2023). Perhaps you have already guessed—Striped Coralroot is a sexually deceptive orchid! In fact, it's the first example of a pseudocopulatory orchid from North America!! (Freudenstein & Barrett 2026)

Corallorhiza striata, Andrey Zharkikh.

Freudenstein and Barrett used an insect net to capture wasps visiting Striped Coralroot flowers. They sexed them by looking for a prominent ovipositor. All 28 were male. Another 13 males were captured and sexed in photographs. The researchers then probed 30 of the flowers visited, and found no nectar. 

To determine what was attracting the wasps, they opened a plastic bag of Striped Coralroot flowers inside a net cone, hoping to release volatile scent compounds. Sure enough, within two minutes a swarm of 10 wasps appeared, flew around the cone, and landed on it (they couldn't get to the flowers).

And the stripes? The authors found no obvious resemblance between flowers and female wasps, but the "red stripe down the center [of the lip] flanked by two lighter patches could signal a wasp metasoma" (a body segment). I wonder—how might one test this hypothesis?

Whatever the attraction, all visiting wasps were the same kind—Pimpla pedalis, which is parasitic on the Pale-Winged Gray, a moth that defoliates Eastern Hemlock. In other words, the orchid dupes a wasp that is parasitic on the larvae of a moth that harms trees. Go Coralroot! (3)

If you are unable to view Pimpla pedalis "mating" with Corallorhiza striata (above), go to Freudenstein & Barrett 2026 (open access) and download the video in Supporting Information at the bottom of the page. Or try this video narrated by David Attenborough. It includes neither Striped Coralroot nor Pimpla pedalis, but is quite entertaining!

Now it's time to leave the Coralroots and move on to orchids with morals as well as beauty, perhaps Cypripedium (Lady's Slippers).

"As Orchids are universally acknowledged to rank amongst the most singular and most modified forms in the vegetable kingdom ... examination of their many beautiful contrivances will exalt the whole vegetable kingdom in most persons' estimation." (Darwin 1862, italics mine)

Cypripedium (Darwin 1862).

Notes

(1) Darwin's book includes exotic as well as British orchids. He received many specimens after reaching out to colleagues and collectors.

(2) Darwin is referring to resupination, which is common in orchid flowers. In bud, the lip petal is oriented upward, but by the time the flower opens, the ovary (sometimes the flower stalk) has twisted enough to orient the lip downward. See The Upside Down World of Orchids.

(3) In the orchid's ruse, Freudenstein and Barrett saw the opportunity for an especially alluring title: "Corallorhiza striata is the first example of a pseudocopulatory orchid in North America and an instance of 'double deception' in fully mycoheterotrophic plants." Wow, that's so cool! But wait ... is this really double deception? That depends on your opinion of Coralroots after reading last month's post.


Sources (in addition to links in post)

Ackerman, JD, et al. 2023. Beyond the various contrivances by which orchids are pollinated: global patterns in orchid pollination biology. Botanical Journal of the Linnean Society 202:295–324. https://doi.org/10.1093/botlinnean/boac082 

Britannica. Orchid/natural history/pollination. Accessed August 2026.

Darwin, Charles. 1862 (1904, 7th printing of 2nd edition). The Various Contrivances by Which Orchids Are Fertilised by Insects. London: J. Murray. https://doi.org/10.5962/bhl.title.84436

Freudenstein, JV, and Barrett, CF. 2026. Corallorhiza striata is the first example of a pseudocopulatory orchid in North America and an instance of“double deception” in fully mycoheterotrophic plants. American Journal of Botany 113(4): e70185. https://doi.org/10.1002/ajb2.70185

USDA Forest Service. Coralroot Orchids. The Celebrating Wildflowers—Beauty of It All website is a joy to wander through! I wish I knew whom to credit for it.

The Monthly Orchid: Coralroots—parasitic cheats or just slackers?

I walked right by these Coralroots! Fortunately I returned the same way and saw them.

Welcome to the The Monthly Orchid, a series of blog posts about South Dakota orchids. This one features Coralroots, genus Coralloriza—small inconspicuous plants but surprising or even shocking in their ways. After considering their manner of living, you can share your opinion of them in a Comment.

Five Coralroot species grow in South Dakota, all in the Black Hills. But the rest of the state is not nearly as well botanized as the Hills, and these little orchids may be lurking in shady hardwood forests far to the east. I wouldn't be surprised; four of our species occur nearby in Minnesota.

Coralroots are short, slender, drab, and easily overlooked. Stems come in a range of muted colors—red, brown, purple, yellow, occasionally greenish. Color can vary widely among populations of a single species, based on genetics and environmental factors, for example soil acidity.

Kneeling on the forest floor, we see a Coralroot's subtle beauty (Corallorhiza maculata).

Corallorhiza maculata, yellow population (USDA Forest Service).

Yellow Coralroots (Corallorhiza trifida) may be nearly green; but whether they can photosynthesize isn't clear (USDA Forest Service).

Like most orchids, a Coralroot begins life as a seed the size of a speck of dust, housed in a capsule with many thousands of its siblings. When the capsule dries and splits, the seeds are cast to the wind. Being so tiny, orchid seeds have NO endosperm—none of the nutritive tissue that most angiosperms (flowering plants) provide their embryos. So to germinate successfully, they must find help.

With luck, a Coralroot seed lands on a shady moist site with a network of fungal tissue (a mycelium) on or near the soil surface. If the fungus is the right kind—one that can form partnerships with plants (mycorrhizae)—there's a chance that germination will succeed.

Fungal mycelium—a network of hyphae that delivers water and nutrients to whatever is connected to it (Kirill Ignatyev).

When the seed germinates, the tiny embryo develops into a protocorm—a mass of cells less than a millimeter tall just beginning to differentiate. The basal cells allow a strand of fungal tissue to enter, but keep it from spreading further. This is the connection that will nourish the baby orchid. At this point, roots would begin to develop as well, but not in Coralroots. Instead, a short branched rhizome with rounded bumps begins to grow.

Rhizome of Corallorhiza (right) looks like coral, or did to Abraham Gagnebin, who named the genus in 1755 (USDA Forest Service).

Once above ground, most orchids start making their own food via photosynthesis, in tiny green solar-powered food factories in their leaves (and sometimes stems). But Coralroots have no leaves, only bladeless sheaths, and they are rarely green.

Corallorhiza innata (= C. trifida); note short branched rhizome and sheaths on stems (W. Muller 1904).

How do Coralroots survive without roots or leaves? For many years, they were thought to be saprophytic, decomposing and living off organic matter in the soil. Some reputable botany websites still describe them as such. But in fact, they cannot decompose organic matter. Instead, they're part of a complex drama, featuring three very different players.

Most orchids end their fungal dependency after germinating, but a young Coralroot can't. Without photosynthesis it needs a source of food, and will rely on the fungus for the rest of its life. But wait ... fungi don't photosynthesize either! This is where things get complicated.

Tripartate relationship: tiny orchids, fungal network, tree. Note that NO arrows come from the Coralroots.

If we search underground, just beneath the soil surface, we see that the fungal mycelium is linked not only to baby Coralroots, but also to tree roots, in a mutually beneficial relationship. A tree makes carbon compounds via photosynthesis and shares them with the fungus. In return, strands of fungal tissue increase the tree's uptake of water and minerals. Most importantly, the fungus fixes nitrogen in a form the tree can use.

However, while the trees and fungi are helping each other, the Coralroots continue to suck up nutritious carbon compounds from the fungal mycelium. From whence come such compounds? Might they come from dead organic matter decomposed by the fungus? Apparently not. Studies have shown that carbon delivered to the Coralroot by the fungus is produced by photosynthesis, not decay. Trees are the ultimate source.

Knowing this, what are we to think of Coralroots, those delicate little beauties of the forest? They live off carbon produced by trees and delivered by fungi, and contribute nothing in return ... NOTHING! Some botanists call them "heterotrophs" (consumers) that eat fungi. But "parasite" is more widely used and perhaps more accurate, given that they suck nutrients from fungal tissue. And yet no harm to the host has been shown. It's probably best to call Coralroots "mycoheterotrophs"—an awkward but nonjudgemental term specific to their tripartite relationships (Leake 1994).

USDA Forest Service.

What do you think of Coralroots? Do you forgive them their selfish ways? It's tempting to do so, but be aware—they have another dark side, and it has to do with sex! Stay tuned.

Sources (in addition to links in post)

Britannica's mycoheterotrophy article is detailed, interesting and clear. Here's their summary, my insertions in brackets:

"Mycoheterotrophs leach the carbohydrates that the fungi obtained from symbiotic plant partners [trees] and provide no reciprocal benefits. This interaction creates a tripartite relationship involving the autotrophic plant [tree], the fungus, and the mycoheterotrophic plant [Coralroot], with the mycoheterotroph serving as the ultimate sink for the carbon fixed by the autotrophic plant."

Leake, JR. 1994. Tansley Review No. 69. The biology of myco-heterotrophic ('saprophytic') plants. New Phytologist 127:171-216. Free access.

Leake, JR. 2005. Plants parasitic on fungi: unearthing the fungi in myco-heterotrophs and debunking the ‘saprophytic’ plant myth. Free access. 

USDA Forest Service. Celebrating Wildflowers: Coralroot Orchids. This is a wonderful website, offering so much for us to enjoy and learn! I wish I knew whom to credit. Accessed July 2026.