Tag Archives: Texas

Just Add Water: Annual Wildflowers in the Chihuahuan Desert

Prairie evening primroses dot a pasture near Fort Davis, Texas.

My friend, John Karges, and I were talking yesterday about the amazing spring that we’re having. He laughed and said “Add water and the desert will stir itself.”

How true.

We’ve had an extraordinarily wet winter and spring this year. Deep, soaking rains and frequent snow (and ice) storms encouraged a wildflower display that few can remember ever seeing in the Chihuahuan Desert region. Big Bend bluebonnets create a blue haze on the hillsides; the delicate, white petals of prairie evening primrose look like a tissue-box explosion in pastures; and mustard plants emit a perfume so sweet it’s cloying at times.

Big Bend Bluebonnets along the River Road in Presidio County Texas.

Even the stems of the cacti are so swollen with water they look like they’re going to burst. Instead, they’ve burst with flowers, dozens of blossoms covering a single plant.

The desert is in bloom. It’s a marvelous sight to behold.

Mustard wildflowers carpet a pasture in the Chihuahuan Desert near Marathon, Texas.

But where do all these flowers come from?

Most of the time, the Chihuahuan Desert is a pretty harsh environment. It’s dry (especially in the winter) and the rain that we do receive tends to come in the summer during highly localized thunderstorms that may drench one spot but leave a broad area dry as a bone.

To cope with the heat and the unpredictable precipitation patterns, desert plants have an amazing array of adaptations aimed at holding on to moisture: small leaves, fine hairs that protect the leaf surface, and a splendidly specialized photosynthetic process.

But during years like this one, we’re reminded of the most amazing adaptation of all: being an humble annual.

Annual plants are those that go from seed to seed in a very short time. When conditions aren’t favorable, the seed just doesn’t sprout. It sits in the soil, waiting for the perfect combination of moisture and warmth that will increase its chances of survival.

Dense patches of the annual wildflower curvepod scrambled eggs were common at higher elevations in the Chihuahuan Desert.

This life cycle isn’t unusual—in fact, approximately 13% of the world’s flora consists of annuals. But if you look at the flora of a typical desert, you’ll find something very different. In the aridlands of the world, annuals can make up 40% or more of the desert flora. Think about it. Nearly half of the plants growing in a desert won’t even make an appearance until there’s some hope of surviving long enough to be pollinated and set seed.

The seed of many desert annuals can survive for years—decades even—before the conditions are perfect for growth. On occasion, they get fooled, though. A good soaking rain followed by heat, wind, and dry conditions may spell doom for an overeager annual.  Long-term survival depends on mechanisms that discourage a portion of seed from growing even when conditions are just right.

But sometimes, spring conditions are just too favorable for any plant to remain snug in its seed jacket. This is one of those years. Good rains and warm day-time temperatures have encouraged the growth of hundreds of thousands of annuals. Early in the spring, clay flats in the Big Bend region were covered with turtleback—its gray-green leaves and cream-colored flowers forming a soft carpet across the landscape. Stands of lyreleaf twistflower (you’ve just got to love the name) sent their spikes of purple, urn-shaped flowers above the grasses, and curvepod scrambled eggs had even the plant enthusiasts scratching their heads. Where did they all come from?


Naked turtleback creates a green haze in the Chihuahuan Desert of Big Bend National Park, Texas.

 

Naked turtleback in the clay flats of Big Bend National Park, Texas.

The desert is truly spectacular this year and every week it changes. We’re still getting rain, so the show will go on. If you’ve been putting off your annual pilgrimage to the Chihuahuan Desert, it’s time to quit procrastinating, pack your camping gear, and come on out. This truly may be a once in a lifetime experience.

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Chihuahuan Desert Ferns

Cheilanthes fern, Fort Davis National Historic Site, TexasNormally, I’m outside every day in September enjoying the cooler temperatures, brilliant sunshine, and abundant life inspired by the afternoon thunderstorms of the monsoon season.

But not last week.

Rain (torrential at times), heavy cloud cover, and temperatures in the low 50s kept me huddled in the house muttering about the imminent arrival of the next Ice Age. As I stared morosely out the window, watching the rain drip from the roof, I began to wonder: What happens to the butterflies, bees, and bugs when the temperatures go from warm and dry to cool and wet in a single day?

Thinking this was the perfect subject for a blog (I’m sure you’ve all been dying to know), I donned my rain jacket, grabbed my camera gear, and wandered through the mist to the Fort Davis National Historic Site. Although chiefly known for the 19th century fort buildings, they also have a wonderful nature trail that loops from the fort site, up the ridge that separates the Fort from Davis Mountains State Park, and back down again. Here, I was sure I would find my sleeping bugs.

I probably would have, too, if I hadn’t gotten distracted. Every place I peered and poked for insects, I was confronted by ferns. Beautiful, lush, green ferns. The magic of desert rain.

Dancing Bommeria, a Chihuahuan Desert fern, growing near Fort Davis, Texas.Most people don’t hot-foot it to the desert to look for ferns. But perhaps they should. According to botanists Sharon Yarborough and Mike Powell, there are 64 different types of ferns that grow in the Trans-Pecos region of Texas.

Ferns can grow in the desert because they’re experts at finding little microhabitats that are just a tinier bit wetter than the surrounding landscape. Look for them growing from cracks in the rock, under the shelter of a tree, or peeking out from beneath a boulder. Depending on when you look, though, you may not be overly impressed. In fact, during most of the year, desert ferns are brown, crispy, and look—well—dead.

Chihuahuan Desert ferns dehydrate during the warm, dry months and wait for rain.But fear not! Playing dead is just one of the many adaptations that ferns have for surviving in the desert. And what an adaptation it is. Your average plant can drop to about 75% moisture content before it begins to wilt and beg for water.  Creosote, one of our common desert shrubs, can lose about half its moisture before it begins to look a bit peaked.

But the ferns. Oh, the ferns. They are the masters of dehydration. During the dry season, some species can desiccate to less than 6%—or as dry as many seeds—but begin to green up, unfurl, and grow within an hour after a refreshing rainfall. When it dries up again, so do the ferns.

But ferns don’t give up their moisture easily. They may be able to survive as a brittle frond, but life is better when you’re green and photosynthesizing. So to stay green as long as possible, the ferns (and many other desert plants) have ways to reduce moisture loss.

Small Leaves

Small Leaves

Waxy Coating

Waxy Coating

Protective Hairs

Protective Hairs

Thickened Leaf Margins

Thickened Leaf Margins

Small is better. Most desert ferns are much smaller then their rainforest cousins. Remember that during the process of photosynthesis the plant takes in carbon dioxide and releases oxygen and water as a waste product. The smaller the leaf, the less water is released.

Be waxy. Most water is lost (transpired) from special cells on the leaf called stomata. These 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. To help protect from this “incidental” water loss, many of the ferns have a cuticle of waxy deposits on the leave surface that make them thicker and seal in the water.

Get hairy. Have you noticed how many ferns are grey and fuzzy? If you look closely, you’ll notice that the color is due to a dense coating of hair. These light-colored hairs serve a couple of purposes. First they reflect light making the leaf surface temperature cooler and they efficiently trap rain, dew, and other forms of moisture to raise the humidity around the leaf surface. Keeping the air surface immediately around the leaf cooler and more humid reduces the evaporative demand from the atmosphere.

Thick leaf margins. The last defense against moisture loss is the ability of the leaflets to roll, thus protecting the surface and the spores. Many fern leaflets have thickened margins that enhance the ability of the leaf to roll.

Not all ferns found in the desert have these adaptations for dry conditions, though. Others simply seek places where there is enough moisture. Delicate maidenhair ferns, for example, can be found on many shaded rock faces with perennial seep springs. You can find these beautiful ferns at the bottom of Modesta Canyon at the Chihuahuan Desert Nature Center or in the grotto at Ojito Adentro, Big Bend Ranch State Park.

Water Clover (Marsileaceae) is a Chihuahuan Desert fern that grows in puddles during the rainy season.But my favorite fern is the water clover. This aquatic fern survives the dry season as a packet of spores (sporocarp) in the mud of ephemeral pools. When the rainy season arrives and the pools fill with water, the gelatinous interior of the sporocarp swells, rises to the water surface and splits, releasing the male and female spores. Once they do what males and females do, the newly fertilized embryo sinks to the bottom of the pool, takes root and begins to grow, eventually spreading its four leaflets across the surface of the pool to begin the cycle of life again.

It’s starting to rain. Time to go look for ferns!

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