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.

The Monthly Orchid—an introduction

The pouch-like lips of Fairy Slippers (Calypso bulbosa) are exquisite with their purple patterns and bright yellow hairs. No wonder fairies collect them at night to wear for dancing! (NPS)

Once again, I'm starting a series of posts about South Dakota plants—in part so that I can learn more about the state's flora (I'm still contributing to the online guide). In 2024 I wrote about trees, mostly the less familiar ones from the eastern part of the state. Last year I focused on ferns and fern relatives (lycophytes), and became a pteridomaniac in the process!

This year, after writing descriptions for sedges and rushes, and while starting on grasses, I considered doing a series about graminoids. But after a few weeks of struggling with species differentiated by tiny green structures, I came to my senses and went in a totally different direction—orchids! Their flowers are colorful, sweet-scented, diverse, relatively large, and highly-evolved.

Twenty-seven native orchid species have been reported from South Dakota. Some have large colorful flowers. Others have sweet-scented flowers, or flowers with unusual parts (e.g. threadlike or deeply dissected petals). But most of our species have flowers that aren't showy. They're small and subdued in color—white, greenish, yellowish, or brownish red. But up close they're gorgeous and obviously orchids.

Spotted Coralroot (Corallorhiza maculata); the white lip with purple spots has yellow gobs of pollen hanging over it; lip c. 6 mm long (MWI).

Like almost all orchids (99%), ours have a combination of features unique to the family: a LIP petal (tepal), a COLUMN consisting of the stamen(s) and pistil, POLLINIA made of pollen grains, and minute SEEDS.

Parts of an orchid flower (Serena Aceto).

The LIP or labellum is one of an orchid flower's six tepals (three sepals and three petals). Five of the tepals are more or less alike, but the lip is quite different—in shape, color, size and more. It's also distinctive among species, and is used in identification (fortunately it's easy to see). The lip appears to provide a landing platform for visitors, and species-specific forms are thought to be designed for specific pollinators—the product of coevolution.

Stream Orchid (Epipactis gigantea) has lips with "tongues"; these move when the flower is bumped, hence its other name: "Chatterbox"; flowers to c. 5 cm wide (Dcrjsr).

The lip of Loesel's Twayblade (Liparis loeselii) is showy relative to the other tepals, 2 of which are horizontal and threadlike; flowers to c. 1 cm long (MWI).

Most orchids have a single stamen, which is joined with the pistil to form a COLUMN. Among species, columns differ in size, shape, color and function. In White Lady's-slipper (below), the top of the column presses against the lip, preventing pollinators from leaving the way they came in. Instead they must exit via a narrow slit in the back of the pouch. Inexperienced bees may take up to 15 minutes to find the exit, and may fall prey to crab spiders lurking within! (source)

Small White Lady's-slipper (Cypripedium candidum) has a glossy white inflated lip to 2.5 cm long; yellow flap with red spots is the column tip (MWI).

In most orchids pollen grains are amassed into POLLINIA, bound together by threads of clear sticky viscin. Pollinia are carried off by pollinators to be deposited (hopefully) on stigmas of the same species. The advantages of dispersing pollinia rather than pollen grains will be explained shortly (below).

Ophrys orchid with a pollinator about to get hit with yellow pollinia (ErwinMeier; arrow added).

Finally, orchids produce the tiniest of SEEDS, which number in the thousands or even millions per flower! This means that there are equally numerous ovules in a single pistil. Now we see the advantage of pollinia. Thousands or sometimes millions of pollen grains packed into a pollinium land on a stigma all at once, ready to fertilize the multitude of waiting ovules.

Orchid seeds are very different in another way. Most flowering plants (angiosperms) have double fertilization, producing seeds with both an embryo and a stash of endosperm to feed the seedling as it starts its life. But not orchids. There is no double fertilization, and the tiny seed contains no endosperm to sustain the baby seedling. Even the embryo is much reduced—just a small mass of mostly undifferentiated cells.

Seed of Autumn Coralroot (Corallorhiza odontorhiza), 0.2 mm long! © Freudenstein 2024, CC BY-NC.

When an orchid's capsules dry and split, millions of dustlike seeds are cast to the wind, seemingly with little chance of survival. And yet orchids are said to be one of the most widespread families of flowering plants, both geographically and ecologically! (Brittanica) Seeds and their strategies are what fascinate me most about orchids, far more than the showy diverse flowers. But this introductory post has gone on long enough. So we will stop here, and let the mystery be for now.

"Orchideae" from Ernst Haeckel's Kunstformen der Natur (1899); see source page for names.

Sources (in addition to links in post)

Arditti, J, et al. 2025. Darwin’s prescient letter regarding orchid mycorrhiza. Lankesteriana 25: 83–102. http://dx.doi.org/10.15517/y157kw10 

Brittanica. Orchid. Accessed May 9, 2026.

Freudenstein, JV. 2025. Orchid phylogenetics and evolution: history, current status and prospects. Annals of Botany 135: 805–821. https://academic.oup.com/aob/article/135/5/805/7901162

Wikipedia. Orchids. Accessed May 9, 2026.