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An Unexpected Find in an Unexpected Place

Arkansas Natural Heritage Commission - Friday, November 04, 2016

Unusual sites often support unusual species. That’s the kind of proven biological wisdom that guides the field staff of the ANHC on a daily basis. Sometimes an unusual site is a rare rock or soil type, or a site with an unusual water source, such as a mineral rich groundwater seep. And sometimes it’s a site with conditions more similar to a far-away place, or to the climate of times long past, than to the surrounding area.

Recently, ANHC botanist Theo Witsell was conducting surveys of glades near the White River in Baxter County. Walking through a large, treeless sandstone glade full of desert plants like western prickly-pear cactus (Opuntia macrorhiza), rock-pink (Phemeranthus parviflorus), and stonecrops (Sedum nuttallii and Sedum pulchellum), he saw what looked at a distance like a small creek running through the middle of the glade. Upon closer examination, however, he saw that this “creek” was actually a long, narrow crack in the bedrock. It was only about a foot wide near the top, and was about 350 feet long. Peering down into the crack from the top he encountered pitch black and noticeably cooler and more humid conditions than were found in the hot, dry glade above. A ledge partway down the crack supported a dense population of a large and unusual-looking fern, warranting a closer look.

After some exploring, Witsell found a safe way down into the crack, which turned out to be a rare “slot canyon” 30 to 40 feet deep, widening from the narrow crack at the top to about 20 feet wide at its widest point near the bottom. The whole area inside was cool and damp. Upon closer examination, the fern on the ledge proved to be spinulose wood fern (Dryopteris carthusiana), one of the rarest ferns in the state, and a species not previously known from Baxter County.

Spinulose wood fern has its main range far to the north of Arkansas. When found this far south, such “northern species” usually occur in unusual pockets of cool, moist habitat and are generally considered “relicts” of past ice ages, when glaciers covered the northern part of the United States, reaching as far south as present-day St. Louis. Prior to this discovery, spinulose wood fern was known in Arkansas only from a few other sites – all with cool, moist conditions like cave entrances in the bottom of sinkholes and bases of shaded bluffs at high elevation sites like Mount Magazine.

“A rare northern fern was the last thing I expected to find on a glade survey,” said Witsell, “but unusual habitats often support rare or unusual species, and there are other rare northern and Appalachian species in that part of the Ozarks”. One example is the recent discovery of broadleaf bunchflower (Veratrum latifolium) from nearby Stone County.




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