Revisiting an Unexpected Fern Find

Dane County, Wisconsin - May 17, 2025

Two years ago, almost to the day, I was wandering a high quality dry-mesic prairie when my eyes landed on something I was only accustomed to seeing in sand dunes of the northern Great Lakes: the tiny form of an immature moonwort fern (Botrychium) emerging from the sandy soil. At the time I had no idea that it was even possible to see a moonwort in south-central Wisconsin, so this came as a complete surprise. After some careful keying and confirming with an expert, I was able to determine that the plants were the state endangered Prairie Moonwort (Botrychium campestre). Moonworts are in strong contention for my favorite group of plants, so it was a thrill to find a new species for me, and one so rare at that! Just a few weeks later I returned to see mature plants, but by then they'd been nuked by 95-degree temperatures and lay desiccated on the baking sand. Last year they didn't appear to emerge at all. This year, though, the plants emerged again and in much larger numbers than 2023. I was happy to visit the site and see a large and thriving population of this strange plant.

How Botrychium campestre looked when I found it in May 2023. Tiny!

This preserve has repeatedly proven itself to be the highest quality prairie I've ever visited, with numerous breeding birds, excellent insect diversity, a remarkable flora including several rare plants, a notable lack of non-native species, and spectacular floral displays throughout the growing season. This afternoon, I was immediately distracted by a dazzling display of Prairie Phlox (Phlox pilosa), Eastern Shooting Star (Primula meadia), Hoary Puccoon (Lithospermum canescens), Yellow Star Grass (Hypoxis hirsuta), Robin's Plantain (Erigeron pulchellus), Bird's-foot Violet (Viola pedata), and hundreds of the uncommon Seneca Snakeroot (Senega officinalis). Against my better judgement but not able to help myself, I slowly moved through this explosion of spring wildflowers as heavy clouds moved in, dimming the sunlight and making my eventual efforts to photograph the moonwort substantially more challenging.

The profusion of spring wildflowers is found on one of two dolomite caps at the site. This bedrock provides a richer soil - hence the incredible number of blooms - as well as an erosion resistant layer which prevents the hill from eroding downward. I needed to descend to a low saddle between the two dolomite caps, where the dolomite isn't present, allowing a soft layer of underlying sandstone to freely erode away. It is only in the lowest part of this saddle, where the soil is poorest, sandiest, and most free of competition, that the ferns can be found. I was happy to find several immediately upon arriving in the right area.

Context for one of very few occurrences of Botrychium campestre, or the genus in general, in inland southern Wisconsin. The first image looks from one dolostone cap across to the other, with the plants found in the lowest portion of the sandstone saddle between - near the young lone oak tree. The second picture shows species-poor sandy soil, including a moonwort at lower right.

B. campestre forming a distinctive cluster of stems.

Botrychium is an infamously difficult genus, but thankfully B. campestre is one of the easier species to identify. It is one of a small handful of species that commonly form tight bunches of stems, resulting from the production of clusters of underground gemmae. It is one of few which are known to grow in the prairies of the Great Plains and Prairie Peninsula. It is also distinctive for the following combo of traits: it emerges quite early compared to other species; the sterile blade (the "leaf") is almost succulent and folded lengthwise; there are 4-5 pairs of narrow segments on the sterile blade, most ending in a notch or two; and the fertile blade (the spore-producing "grapes") is at most 1.5x longer than the sterile blade.

The plants at this Dane County prairie possess all of the above characters, and despite being quite local, they are evidently happy here. I was eventually able to count over 400 stems, mostly occurring as loose groups of 10-50. It is encouraging to see a population of an endangered plant doing so well, although there is a caveat: I suspect the plants' failure to emerge last year as well as noticeable browning this year are due to spring burns which have happened annually since I started visiting this site in 2022.

For a plant as fragile as Prairie Moonwort, a poorly timed spring burn can surely heat the ground enough to damage plants, even before they emerge from the soil. Additionally, moonworts are thought to be strongly mycoheterotrophic, meaning that they rely heavily on stability in the soil's biotic community wherever they occur.

A cluster of Botrychium with varying fire damage - from yellowed to scorched. Fire damage can also be found on most other photos in this post.

Frequent burning may damage the organic and fungal components of soil, leading to declines in Botrychium. There is abundant evidence that nowhere in the Midwest should burn close to annually, making annual spring burns confusing at best and highly damaging at worst (with observations across the central and eastern states favoring the latter). This is a problem for many fire-sensitive species throughout much of the continent. I hope the practice of frequent spring burns - seemingly an overcompensation from the era of Smokey the Bear - gets critically reevaluated by the land management community sooner rather than later.

Regardless, what a joy it was to revisit my find from two years ago and find such a thriving population! These ferns add one more compelling plant to cement this place as one of my all-time favorites. I am sure it will be featured here again.