Desert Ferns

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Most people don't rush to Big Bend National Park to look for ferns. But perhaps they should. At least 36 fern species grow in the park. They're worth searching for because of their names alone. Who can resist a villous lipfern? Or a purple cliffbrake? How about a wavy scaly cloakfern?

 

For most of the year, ferns survive by drying up and waiting for the next rain.

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Survival Tricks

Ferns grow in the desert because they finesse the system, finding microhabitats that are just a tinier bit wetter than the surrounding landscape. Look for them growing among fractured rocks, under a tree, or peeking out from beneath a boulder. Depending on when you look, though, you may not be overly impressed. Most of the year, desert ferns are brown, crispy, and look—well—dead.

But fear not! Playing dead is just one of the many adaptations that ferns have for surviving desert heat and aridity. Your average plant can lose about 25% of its moisture content before it begins to wilt and beg for water. Creosote, a common desert shrub, can lose about half of its moisture before it starts to look a bit peaked.

But the ferns. Oh, the ferns. They are experts at dehydration. During the dry season, some species lose over 90% of their moisture content. But they begin to green up, unfurl, and grow within an hour after a refreshing rainfall. When it dries again, so do the ferns.

But ferns don't give up their moisture easily. They may survive as a brittle, brown frond, but life is better when you're green and photosynthesizing. So to stay green as long as possible, the ferns have ways to reduce moisture loss.

 

Many desert ferns are very small.

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Small is Better

Most desert ferns are more petite than their rainforest cousins. Remember that the plant takes in carbon dioxide during photosynthesis and releases oxygen and water as a waste product. The smaller the leaf, the less surface area from which water can be lost.

 

Look closely at a desert fern. Many are covered in fine hairs to protect the leaf surface from drying.

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Get Hairy

Have you noticed how many desert ferns are grey and fuzzy? The color is due to a dense coating of hair-like fibers. These light-colored hairs serve a couple of purposes. First, they reflect light, making the leaf-surface temperature cooler. Second, the hairs trap rain and dew to raise the humidity around the leaf surface. Keeping the air immediately above the leaf surface cooler and more humid reduces the atmosphere's evaporative demand.

 

Some ferns, such as this Wright's cliffbrake, have thickened leaf margins to allow the leaf to roll and protect the surface from drying.

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Be Waxy

Most water is lost (transpired) from specialized cells on the leaf called stomata. These cells open and close to absorb and release gases (carbon dioxide, oxygen, and water). But other parts of the leaf surface and stem can lose water through simple evaporation. Many ferns have a waxy cuticle on the leaf surface to help reduce incidental water loss. The cuticle makes the leaf thicker and helps seal in moisture.

Thick Leaf Margins

The last defense against moisture loss is the leaflet's ability to roll, thus protecting the surface and the spores. Many fern leaflets have thickened margins that help the frond curl.

 

Lush maidenhair ferns grow above the pool at Mule Ears Springs.

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Fern Spotting

Not all ferns are adapted to desert conditions. Some seek places where there's enough moisture to grow. Delicate maidenhair ferns, for example, cling to shaded rock faces at seep springs such as Mule Ears Springs.

Ferns are harder to find in the low desert, but keep an eye out as you hike the Blue Creek Trail or any enclosed canyon trail. Your best chance for ferns? Head up to the Window Trail, the Lost Mine Trail, or make your way into the high country. It seems counterintuitive, but the best time to find ferns is after the monsoon rains begin in July or August. The ferns will be lush, green, and begging to be noticed.

 

Learn More

To learn more about the ferns of Big Bend National Park and the surrounding region, check out this field guide:

S.C. Yarborough and A. M. Powell (2002). Ferns and Fern Allies of the Trans-Pecos and Adjacent Region. Texas Tech University Press.