An Orchid Reveals its Secrets

By Stephen Packard and Lisa Musgrave

 

Dozens of volunteers have been “species stewards” for the prairie white-fringed orchid (Platanthera leucophaea) – a plant on the federal Threatened list. Most of the earth’s small populations of this species are in “The Prairie State” – and volunteers for the United States Fish & Wildlife Service (FWS) carefully monitor every known population. In 2023, a very dry and poor year for these orchids, a total of 223 plants were found at nineteen Illinois sites. At twelve of those sites, five or fewer orchids were recorded. Non-blooming plants can be hard to find; many more plants were likely surviving as leaves only, building their roots and waiting to bloom in a year with better weather. When the FWS approved its national Recovery Plan for this species and began recovery efforts in 1991, the Somme effort was adopted as a model. Seed is spread to potential good habitat, and at many sites emerging plants get “intensive care” to allow populations to build. Illinois numbers have varied from a low of 109 plants in 2006 to a high of 2,287 plants in 2020. In that good year, Somme contributed 540 plants to the tally. The United States Fish & Wildlife Service annually takes pollen and seeds from Somme to begin or enrich populations elsewhere.

Orchid in "Intensive Care." A stake of cut brush supports a deer-exclusion cage. Inside it is a vole-exclusion cage. The pink flagging indicates that this orchid has been hand pollinated.  

In more than four decades of careful work and study, the Somme Team has learned:  

• These plants don't stay put.
• A “fairy ring” of orchids suggests a possible explanation.
• Widely broadcasting seed can produce dozens to hundreds of new plants.
• Habitat management is key.

Details below: 

These plants don't stay put.

Unlike most conservative plants, prairie white-fringed orchids seem to do well in an area for a few years and then disappear, emerging in other areas where we never saw them before or had not for years. We have in some cases initially broadcast seed in various places that seemed good, with no results. Then after maybe ten or twenty years of occasional seed broadcast, we find a plant or two, then in a few years more, and many more for five or ten years, then few or none in that area. It’s happened impressively in at least eight areas at Somme Prairie Grove and Somme Prairie – both Illinois Nature Preserves. 

Orchid pollinia. Orchid pollen doesnt travel to other plants as dust, like most species, but in dense, sticky packages called pollinia. They adhere to a toothpick or the tongue (or head) of a hawk moth by an adhesive patch, shown clearly above. 

A clue from a “Fairy Ring” 

Why do these populations come and go? A curious phenomenon provides a clue. For reproduction, this orchid depends on a fungus. Some mushrooms are frequently found in circles called fairy rings. Such rings form because, as an underground mass of mushroom mycelia grows, it may use up something in the soil, and the advancing front of underground mushroom “mycelia” moves out to areas that have what it needs. When the mushrooms (the spore-bearing “fruits” of the mycelia) emerge, they rise out of that advancing circle. 

Fairy ring mushroom photo from University of Arkansas: https://www.flickr.com/photos/uacescomm/50301990921/ 

We’d never heard of a fairy ring made up of plants, but we found one. For many years, we had broadcast orchid seed in one swale that looked like good orchid habitat but where no orchids had been seen. Then in 2009, finally there was one beautiful orchid. It stood there by itself for years, quite a big one. We caged it and stabilized the cage with a metal stake. We ended up calling that area “the stake area.”

It flowered annually for 8 years (missing one). That’s unusual. Most prairie white-fringed orchids die a year or two after first flowering. FWS research shows that the average life of these orchids after first flowering is 1.2 years.

Then dramatically in 2014, a full circle of 22 orchids arose around the big staked one. The plants in the circle averaged 2.5 meters from the original plant. Most were young plants (“two-leafers”). Over the years, some bloomed, set seed, and passed into history. But many more orchids, gradually spread up and down the swale, farther and farther from the long-gone original orchid.

To reproduce, the almost invisibly tiny orchid seeds must sprout and live underground parasitically or symbiotically with the fungus, sometimes for years, drawing nutrients from the fungus. With this in mind, there are many possible hypotheses that might explain the fairy ring observations. One is that the fungus this orchid depends on is not everywhere in the soil of orchid habitat. The fungus may deplete the resources it needs in some areas as it spreads to others. Perhaps the orchids reproduce successfully only where the fungus is thriving at that time.

Most of these rare orchids only flower for a year or two before dying and making way for new ones. All seed in early years at Somme resulted from hand pollination by trained volunteer stewards, who feel privileged to do it. In recent years, small amounts of "natural" pollination by hawk moths has been observed. 

Numbers of blooming orchids grown from the 190 plants found in 1991 when the U.S. Fish & Wildlife recovery plan began. But annual numbers increase and decrease dramatically. 

Widely broadcasting seed can produce dozens to hundreds of new plants.
We’ve experimented with various approaches to spreading the orchid seed, and more careful experiments are worthwhile. But our only proven practice has been to scatter seeds widely. We like to do it on a windy day; sometimes we just break capsules and wave them around; or we tie capsules on a tall plant and let the wind gradually blow all the seeds in various directions over days or weeks. The seeds find the right places.

One example of an experiment: The Great Transects Test. We measured out a few straight lines near a distinctive glacial bolder in what appeared to be good orchid habitat. Then we marked off intervals, kept careful records, and planted orchid seed by a variety of methods:

• Planting on the surface, just dropping seeds into the prairie duff
• Pulling the duff away and dropping seeds on the exposed soil surface
• Same as above, but we “roughed up” the soil a bit, to get some seeds underneath.

Then, for the latter two approaches, we also tried:

• Mixing seed with sand (making it easier to separate or un-clump the tiny seeds)
• Mixing with cornmeal (because we worried that the sharp sand might injure the seeds) 

This was a lot of work, but science requires that. For the results, we found we did not require a lot of statistical analysis. No orchid emerged in or near any of those transects. A couple of decades later, orchids did emerge in a different part of this swale and gradually spread to the area of the Great Transect.

Question: What’s the meaning of this experiment, in practical terms? Answer: We’re not smart enough to figure out exactly where this orchid ought to be. An individual orchid can make 100,000 seeds. Wind and chance may bring a few of those seeds to the right places to start a new plant.

Orchids typically produce tiny seeds in huge numbers. They blow everywhere, but they contain little beside DNA. They cannot grow into a plant without connecting with a fungus that supplies what most plants get from the endosperm, embryo, radicle, cotyledons and other famous seed parts that most plants have, but orchids do not. 

Orchid capsules, tied to a sunflower stalk, so the seeds can blow around at a new possible orchid area. 

An orchid stem cut and sectioned by voles. Early in the year, voles cut stems of orchids (and other plants) that human hands have touched, as we've seen again and again, perhaps because they smell or taste something that makes them curious. Later in the season, as shown here, voles want to get at the ripening seeds. So they cut the stem at vole height, pull down the rest of the stem, and cut it again, and again, until the seeds are in reach, without the vole having to climb and expose itself to predators. 

Habitat management is key

The very first area where we saw these orchids, four or five years after broadcasting seeds in many areas, worked well as habitat for them for a few years. Then it started growing a dense stand of saw-tooth sunflower. The orchids faded out there, as did the diverse vegetation that had comprised the orchids’ associates. We decided to cut (scythe) those sunflowers a couple of times a year to see what would happen. After a few years, diverse vegetation including a few orchids had returned. Then we moved on to other concerns and experiments. Now that area is dense with gray dogwood - again without orchids. This drama is a reminder that Somme Prairie Grove is still in early-stage restoration (or mid-stage? … time will tell).

The overall goal of the work at Somme Prairie and Somme Prairie Grove is to restore the full diversity of natural prairie and savanna grasslands. The management consists of frequent (annual or biennial) burns, reduction of alien or native invasives, and seeding with locally gathered seed. 

The prairie white-fringed orchid has never been successfully grown in gardens. They live at Somme with some human protection - but much impacted by the challenges of nature. Here the photo shows a vole cage, one orchid stem, many stems of something else that the cage also protects (and thus perhaps has unnatural vigor), that same species clipped by voles to the left of the cage, three young tree or shrub stems that will be controlled by fire or loppers, and a crayfish burrow bringing subsoil to the surface. 

We mostly don’t pay attention to individual species except in the cases of especially rare or conservative ones that seem to need some help getting started. But in time those species will have to make it on their own – in the bosom of the ecosystem. Plants sometimes grow for a while in places where we seeded them, only to fade out as the conservative competition increases and show up where we didn’t seed them, but where seeds of those temporary plants had travelled. Good for them! Over the years, larger and larger areas have become diverse habitat for many conservative species, including this orchid. How much intensive care will it continue to need? In 2020 with 540 orchids, Lisa stopped trying to cage them all.  286 of those orchids bloomed, of which Lisa and team caged 156. Of the uncaged ones, 61 were eaten by deer, about half. Many species at Somme are badly depleted by overpopulated deer and need exclusion cages until the deer population is reduced – if they are to survive at Somme. 

An orchid emerging in late spring. As Lisa says, "They are beautiful even then." We try to find and install deer-exclusion cages at that time, or too many get eaten. 

One rough experiment suggested that the needed hawk moths are now plentiful enough to do at least some of the pollination. The time we stewards spend caging and pollinating is time we can’t devote to other needs of this recovering ecosystem. Still at this point, our impression is that if we stopped intensive care, this federal Threatened species would be lost from Somme … or perhaps merely reduced to a small number of plants. We have little enthusiasm for trying the “no action” experiment now. We continue to learn. The adventure continues. 

Endnote

An earlier blog post on this orchid at Somme is Chapter 1 to this post's Chapter 2. 

Some people ask, aren't you concerned about revealing the location of this rare plant? My first response is always, yes, I'm concerned, but there's a balance to be considered. If no one celebrates rare plants, they won't get the care they need. Many populations have been lost by neglect.

Another response is that that cat is already out of the bag. Somme's orchids are already identified in many books, papers, conferences, and indeed in this blog. 

But perhaps the main reasons that these orchids haven't been poached is that 1) many people realize that this plant is so tied to the ecosystem that if you dig one up, it will just die and 2) the Somme preserves are well populated with caring people who do a great job at keeping an eye on the place. We would call the police, of course, if needed. But it's kind of inspiring that, except for garbage dumping around the edges, only people with reverence for nature seem to spend time here. 

Acknowledgements

Photos by Lisa Musgrave and Stephen Packard

The Somme preserves are owned and management supervised by the Cook County Forest Preserves.

Most of the day to day restoration is conducted by Friends of the Somme Preserves in partnership with the North Branch Restoration Project. 

Thanks to Eriko Kojima for helpful proofing and edits (and certainly more for her fine work on orchid habitat restoration).