Pioneer Valley Fern Society

Unusual Sensitive Ferns

There is always more to look for!

You may remember earlier this season a news article on our noticing the unusual (& often fertile) fronds of the Bracken fern, a common fern and one we hadn't spent much time looking at closely. Now we have found that there is a good reason to look more carefully at another of our common ferns, Sensitive Fern (Onoclea sensibilis). A month or so ago Elizabeth Perry showed us a photo of a very different looking fern she had seen. The closest option was Sensitive Fern, but the fronds were quite different than the normal sterile frond. We got to see a pressed sample in September and decided it must be a weird Sensitive. She and we did further research and found some descriptions of what some people call a form or variant of the Sensitive Fern, which Boughton Cobb's Field Guide to the Ferns (1963 edition) refers to as "the forma obtusilobata...where fertile leaves resemble the normally sterile ones."

As you know, normally the fertile fronds of the Sensitive Fern are very different from the leafy sterile ones, looking more like a cluster of beads on a stem. Apparently this odd combination of fertile and sterile fronds has been discussed and written about in scientific journals, and Cobb included a couple little drawings of extreme examples. All the sources we found described this as happening sometimes after injury from disturbance such as mowing. Elizabeth found these unusual fronds in a mowed area. In 2021 another fern friend, Hugh Roberts, had sent us a photo of a similar strange frond from his yard, but we didn't connect the dots then. It had also been mowed.

It is getting late in the season, but keep your eyes open for these strange and attractive Sensitive Ferns. We did find some at a local site along a wet roadside, where mowing had taken place. Thank you Elizabeth for use of one of your photos.