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Monthly Fern Finale—Moonworts!

"A very singular and very pretty plant ... [leaflets] are rounded and hollowed, and thence its name came of Moonwort" Sir John Hill, 1770. (image from Atlas der Alenflora 1882).

About 2075 years ago, during the first century BCE, Roman philosopher Cicero wrote of introductions—their importance and how they should be constructed (1):

"one's opening remarks, though they should always be carefully framed and pointed and epigrammatic and suitably expressed, must at the same time be appropriate to the case in hand; for the opening passage contains the first impression ... and this ought to charm and attract the [reader] straight away."

After looking up "epigrammatic" (relating to a short saying or poem that expresses an idea in a clever, funny way), I sat down to construct an introduction "appropriate to the case in hand" — Moonworts.

First the epigram, from Botrychium lunaria by Giles Watson.

Hear the latch click in the gloom, Thus gain admittance to the room.
By fern and stealth, no guile nor wealth
Can buy a lock to hinder me.

Now the charm, of which there's no shortage!

After an unknown number of years underground, Botrychium simplex grows a leaf (J. Hollinger). Moonworts (Botrychium species) are attractive little ferns, and it's unfortunate they're rarely seen. They live mostly underground in the intimate company of Glomus—a fungus that forms mutually beneficial subterranean relationships with nearly 80% of vascular plants. Typically Glomus supplies nutrients to the plant, and the plant supplies Glomus with carbohydrates via photosynthesis. But photosynthesis requires sunlight, so how can a Moonwort make carbohydrates if it lives underground? Maybe it's a parasite rather than a partner. This is just one of Moonworts' mysteries.

When conditions are right (another mystery), or perhaps when the stars align, a Moonwort sends up a single leaf. Though distinctive it's difficult to spot, being small, short-lived, and often hidden in vegetation or duff. But lucky is the finder of a Moonwort! If collected by the light of a full moon, the fertile part can be used to pick locks, unshoe horses, and turn mercury to silver.

Moonwort leaf with a sterile leaflike trophophore and a fertile (magical) sporophore; closeup shows sporangia have opened and released spores (Britton & Brown 1913). Mingan's Moonwort releasing spores; soon it will wither and be gone (R&N Crawford). The first known scientific description of Moonwort appeared in 1542, in a revolutionary herbal by physician and botanist Leonhart Fuchs: De Historia Stirpium Commentarii Insignes, Notable Commentaries on the History of Plants. It contained 500 high quality and largely accurate illustrations to help with identification—a novel approach which Fuchs felt obliged to explain: "a picture expresses things more surely and fixes them more deeply in the mind than the bare words of the text." Lunaria minor, from Fuchs's 1542 herbal. BHL Leonhart Fuchs c. 1543 (source). Descriptions in Fuchs's herbal were brief and often "borrowed" from earlier works, an accepted practice. Lunaria minor was said to have a round stem, with a single leaf divided into seven parts and with a stem atop which were seeds (fern reproduction was assumed to involve seeds, though none had been found).

Lunaria minor (the name) and Moonwort seeds would persist for several centuries. Then in 1753, pioneering plant taxonomist Carl Linnaeus put Moonworts in the genus Osmunda (but he too referred to seeds; spores weren't accepted until the mid 1800s). In 1845, Czech botanist Carl Presl moved Moonworts to the genus Botrychium, where they mostly reside today (2), and recognized 17 species. But in the first "modern" treatment of Moonworts, Jens Clausen (1938) reduced this to just six, all of which occurred in both Europe and North America.

We look back on Clausen's classification as much too simplistic. But nearly 50 years would pass before someone took enough interest in North American Moonworts to do something about it—specifically Warren and Florence Wagner, who upped the number to 22. Study and discovery have accelerated since. Currently 38 Moonworts are known for North America (Farrar 2024), with several more species in the pipeline.

A recently-described North American Moonwort—Botrychium farrarii (Legler & Popovich 2024). Note variation. With so many species and such small plants, Moonwort identification is notoriously difficult (3). Characters are often minute (10x magnification helpful). Differences can be subtle, relative, and variable. No wonder we're regularly referred to experts for confident id. And the experts may resort to molecular techniques (e.g. DNA, enzymes) for verification.
So what are we to do in our South Dakota plant guide, aimed at enthusiasts as well as professionals? We shall follow the advice of Leonhart Fuchs, still sound after all these years. High quality photos will accompany relatively brief descriptions. Discussion of lookalikes will note similar species, offer possibly useful differences, and most likely refer the user to technical manuals and experts.
Fortunately, we do NOT have to identify a Moonwort to species to enjoy it! Just finding one is exciting, and examining it closely can be magical. For example ...
Botrychium matricariifolium was named for its twice-divided trophophores, reminiscent of the leaves of matricary (chamomile). It appears to be rare in South Dakota, found at a few sites in the Black Hills. Matricary Moonwort is a relatively large moonwort—to 25 cm tall (MWI). Up close, the trophophore has a lacy elegance (MWI). The branched sporophore has many bead-like sporangia, each one containing thousands of spores! (MWI) Prairie Moonwort, Botrychium campestre, may be our smallest Moonwort. In South Dakota it occurs in grasslands, true to its name. It too appears to be rare, but one never knows with Moonworts! It may be hiding in the grass, or lurking underground for years, waiting for the stars to align. Prairie Moonwort usually is less than 4 cm tall (NPS). Botrychium simplex, Least Moonwort, has been found at widely scattered sites, from grasslands and sandhills in eastern South Dakota to a picnic area in the Black Hills. It's both extremely variable and quite similar to at least four other species in the state, making id extra difficult. Variation in Botrychium simplex—yikes! (compiled from this source). I'm including the next photo because I loved the comment on the field form—"Not expected out here!" That's a Moonwort for you. They seem to do just fine beyond the limits of "typical habitat". But typical habitat may just be where we typically look for them. Obviously we still have a lot to learn! Least Moonwort (center) along a seepy creek in sagebrush steppe in Nevada! (mreala)
And so the Monthly Fern series comes to a close. Thank you for reading, happy holidays to all, and best wishes in the year to come!

Notes
(1) In De Oratore, Cicero was actually addressing speaking, but his advice for introductions seems applicable to writing.
(2) Some former Botrychium species are now in separate genera, though not everyone agrees. In South Dakota we have Botrypus virginianus (Rattlesnake Fern) and Sceptridium multifidum (Leathery Grapefern).
(3) In contrast to seed plants and true ferns, where identification relies heavily on reproductive parts (flowers, cones, spore-filled sporangia), Moonwort identification relies almost entirely on the leaf-like trophophore. What it's shape and size? Is it divided? how many times? For leaflets—specifically the lowest pair—determine shape, margins, and how they attach to the midrib. Compare them to those above ... and more. Small size and variability compound the challenge.
Sources
Farrar, DR, and others? Moonwort Systematics, Ada Hayden Herbarium, Iowa State University. Accessed December 2025. A great resource, with descriptions and photos for many Botrychium species.
Farrar, DR, Gilman, AV, and Moran, RC. 2017. Ophioglossales, in New Manual of Vascular Plants of Northeastern United States and Adjacent Canada. NYBG Press (apparently not yet published—another moonwort mystery).
Farrar, DR, and Johnson, C. 2024. Botrychium subgenus Botrychium: Moonwort biology basics. American Fern Journal 114:10-21. https://doi.org/10.1640/0002-8444-114.1.10
Hill, J. 1770. The useful family herbal: or, An account of all those English plants, which are remarkable for their virtues ... BHL
Legler, BS, and Popovich, SJ. 2024. Botrychium farrarii (Ophioglossaceae), a new diploid Moonwort species from the Bighorn Mountains of Wyoming, U.S.A. American Fern Journal 114:32–48. PDF

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