JIM CONRAD'S
NATURALIST NEWSLETTER
Issued from the valley of the Dry Frio River on the
southern slope of the Edwards Plateau, northern
Uvalde County, southwestern Texas, USA

February 10, 2013

WANDERING FLOCKS OF SPARROWS
About a month ago nearly every day along the little gravel road leading to the cabin I'd be walking or biking along and sparrows, which would remain undetectable in the short grass until they flew up, would flutter into the air, fly a short distance back into the grass or into nearby bushes or trees. They'd fly up only one or two at a time, so it'd take awhile to realize that I was stirring up a sizable flock. I'd try to see them nearby in the grass before they flew up so I could photograph them but they were so well camouflaged that they remained invisible to me until they flew up. Day after day this happened. Sometimes the flock would number at least 50, so here we're talking about a significant rising from the grass that almost seemed magical, birds being spontaneously generated from the Earth, the bird-essence of grass gushing onto the surrounding landscape.

Gradually the little flock must have grown accustomed to me, for as days passed I could approach closer and closer before they began flying up. Also, sometimes it seemed to me that maybe they were fascinated by my daily passage, because they always gathered in grass along the road when they could have easily moved into adjacent wide fields where acres of similar short grass awaited them with no disturbances at all.

So, this week they let me approach near enough for a picture, and I like the picture because it shows exactly how they are as they forage. Typically when I see them it's well into the day when the sun is bright, even glaring, the wind is getting stiff and there's a rugged, hard-bitten, southwestern-Texas-edge-of-desert feeling in the air. The birds all face into the wind, working into it, fastidiously pecking at this or that grass seed. You can see four of the diligent foragers facing a hard south wind blowing up the canyon at http://www.backyardnature.net/n/13/130210sp.jpg.

They're Chipping Sparrows, easily recognizable with their rusty crowns and white eye stripes underlined with black lines running through their eyes. Back in Mississippi one of the best signs of spring is when the Chipping Sparrows' dry, monotonal trills come wafting through the Loblolly Pines on sunny afternoons. However, probably it's too early for them to be trilling there now, nor are they making a peep here. In Mississippi I've not seen such large flocks of them as here. Later in spring their flocks will break up, pairs will form, and males will establish and defend territories of about an acre (0.4ha).

But, now in early February, all that activity belongs to another world for these hard-working, facing-into-the-wind little winter birds who seem receptive to the bother I cause them each day along the gravel road.

Here on the southern boundary of the Edwards Plateau we seem to be on the exact boundary between where Chipping Sparrows are present only during the winter, and where they occur year round.

*****

DANDELIONS FLOWERING
My sense of spring approaching slowly and incrementally was disrupted this week by a rare trip to the nearest town, Uvalde, 35 miles (56km) to the south, for in Uvalde spring is much more in evidence than here at the cabin. The difference is caused less by the fact that Uvalde is farther south than that we're higher in elevation here. Uvalde stands at about 942 feet above sea level (287m) while here partway onto the Edwards Plateau we're at 1647 feet (502m). This difference of 705 feet doesn't seem much -- and when you're traveling north the rise in elevation is hardly discernible -- but it's enough for us to be assigned to a different USDA Plant Hardiness Zone from Uvalde; Uvalde resides in Hardiness Zone 8b while we're in 8a. This slight difference shows up in enormous differences in the natural vegetation. Here in the hills the most numerous tree species is the Ashe Juniper, while around Uvalde junipers are not to be see. Instead there are scrubby, spiny acacia-type trees. Street trees in Uvalde are putting on leaves and the grass is emerald green, while here our few deciduous trees remain leafless, and the grass still is mostly dun colored.

Though here it's been hard to find any flowering plants at all this week, in Uvalde's lawns and weedy lots it's easy to see flowers on the kinds of weedy, invasive plants that typically blossom in early spring across North America. For example, at my foot the moment I opened the door upon arriving in town there was the native Eurasian herb shown at http://www.backyardnature.net/n/13/130210tx.jpg.

Everybody knows that that's a Dandelion, TARAXACUM OFFICINALE. In the picture the Dandelion's leaves are the larger, arrow-shaped ones emerging from a mat of smaller bur-clover leaves.

Humanity is divided into those infected with the cultural notion that Dandelions are ugly and need to be uprooted from lawns, and those who are touched and pleased by the Dandelion's graceful, beautiful and generous presence in a lawn, and I'm in the latter group. For me, that day in Uvalde, seeing the flowering Dandelion so magically alive amidst all that tender spring greenness was simply a gift.

William Wordsworth wrote, "We murder to dissect," and there's something to that. However, as an Earthly animal with certain claims upon resources around me, such as the right to take what I need as nourishment, I've plucked the leaves of many Dandelions to eat. That day in Uvalde, needing a different kind of sustenance, I plucked the yellow flower head in the above picture, broke it open and looked, for somehow I needed to assure myself that the laws governing the geometry of flowers still were in force, and that they were as spiritually nourishing as ever. You can see the broken-open flower head at http://www.backyardnature.net/n/13/130210ty.jpg.

Dandelions are members of the Composite, or Sunflower, Family, so the Dandelion's yellow sunburst is a collection of flowers, a head, not a flower itself. In the above picture it looks as if many milk bottles are clustered near one another, and that some of the bottles are broken, with milk running here and there. There's white fuzz spewing from each bottle's mouth, and a long, yellow ribbon or strap-like affair tied to each mouth rim.

In that picture, each bottle is a future fruit produced by a single flower -- one fruit per flower. When speaking of the Composite Family such fruits technically are referred to as cypselae. The milk is white latex issuing from the plant's vessels broken by my dissection. The white fuzz atop each cypsela forms the pappus, which later will become the cypsela's white "parachute" when it launches into the spring wind. The yellow strap is the flower's corolla. If you follow some yellow straps upward you encounter features proving they are corollas, as shown at http://www.backyardnature.net/n/13/130210tz.jpg.

Notice that every corolla is tipped with five little teeth, or dentations. These are vestigial remnants of the five petals of flowers of simpler, more primitive ancestors. "Primitive," because members of the Composite Family occupy an outer branch of the evolutionary Tree of Life -- meaning that in terms of evolutionary history they arose fairly recently from less highly evolved ancestors. The first fossils of flowering plants, or angiosperms, have been found in rock strata about 135 million years old, but fossil pollen from Composites doesn't show up until around 25 million years ago.

In the above picture the Y-shaped items are branched styles with stigmatic surfaces along their inner faces. The stigmatic surfaces are where pollen grains germinate and send their male sex germs down in rootlike tubes through the styles to ovules in ovaries in the milk-bottle-like future fruits at the flowers' bases.

What a pleasure seeing that all is in order with this little flower. What a pleasure knowing that many more Dandelions will be appearing as spring blossoms all around us.

*****

BUR CLOVER
Yellow Dandelion heads were sunbursts in the clover covering the springy lawn in Uvalde, but the clover's true identity was a little less certain.

For, the clover definitely bore clover-like leaves, but its flowers weren't white or purplish like those of the common clovers back East, nor were its flowers grouped in spherical heads or long spikes like most common clover species. The flowers were yellow and usually only three or four formed a cluster. You can see a sprawling stem of the plant with its few tiny, yellow blossoms at http://www.backyardnature.net/n/13/130210mg.jpg.

So, was this really a clover? Clover species belong to the Bean Family and are members of the genus Trifolium. Trifolium species bear conspicuous stipules, and that's also the case with this species. At the top of the above picture note the slender-toothed stipules encircling the stem where petioles attach to the stem. So, that supports the notion that this is a real clover.

However, pulling a flower cluster closer you can see something that wasn't-clover-like at all. That's shown at http://www.backyardnature.net/n/13/130210mh.jpg.

At the right in that picture you see a flower with its five yellow petals arranged in the way you'd expect of a Bean Family member (papilionaceous). Beside that blossom there are also four other flowers who already have been pollinated, their yellow corollas have dried up, turned brown, and are about to fall off, and now where each blossom once stood there's a coiling up green thing covered with low prickles. These are the flowers' ovaries enlarging into spiny, coiled-up fruits, or legumes.

When you see a plant that in every way looks like a regular clover except that it has few flowers per cluster and its maturing ovaries develop into spiny, tightly coiled legumes, you have a bur-clover, a member of the genus Medicago. Our species is MEDICAGO POLYMORPHA, an invasive originally from Eurasia but now scattered across North America and other parts of the world, especially in warmer parts. It goes by such English names as Californian Bur Clover, Toothed Medick, Toothed Bur Clover, Fimbriate Medick, Toothed Medick, and more. The "bur" in these names refers to the prickly legumes which when mature can stick to passing animals' fur for fruit dispersal.

The word medick is an old one, from Middle English medike, which came from the Latin medica, which itself arose from the ancient Greek medike, which was the abbreviated name of Medike poa, which literally meant "Median grass," so called because the plant was imported from Media to Greece during the Greco-Persian Wars from 560 to 500 BCE. At that time the Median Empire occupied a large swath of land extending from present-day Turkey to Pakistan.

About 83 species of the "medick" genus Medicago are recognized, of which Alfalfa, Medicago sativa, is the most famous. Field marks distinguishing our Medicago polymorpha in Uvalde from most other Medicago species include its stipules' long, slender teeth and the spines on its loosely coiled legumes.

The species is regarded as a good forage plant, though some might say it can't beat its cousin Alfalfa.

Ecologically, root nodules on Medicago polymorpha harbor the bacterium Sinorhizobium medicae, which is capable of nitrogen fixation, the nitrogen fixed being made available as a critical nutrient to other organisms in the ecosystem.

*****

ROUGH LIP FERN
Within walking distance of the cabin already two species of lip ferns, genus Cheilanthes, have been found, and this week a third one turned up. Lip ferns in general are frilly, wiry little ferns usually found growing from cracks in rocks or on very thin soil atop rock. They're in the Maiden Hair Fern Family, so their tiny spore-producing bags, or sporangia, are lined up along leaflet margins, usually with the leaflet margins curled around and sheltering them. Before enjoying this week's "variation on the lip fern theme," you may like to review how our other local lip ferns express their lip-fern-ness. There's the Alabama Lip Fern at http://www.backyardnature.net/n/x/alipfern.htm and the Eaton's Lip Fern at http://www.backyardnature.net/n/x/lipfern.htm.

This week's lip fern, much smaller than the others, is shown emerging from a crack in limestone at http://www.backyardnature.net/n/13/130210ch.jpg.

The fronds in that picture were only about two inches long (5cm) and their upper surfaces were covered with slender, stiff, short hairs as shown at http://www.backyardnature.net/n/13/130210ci.jpg.

Another important field mark for this species is that the blackish rachis from which frond segments, or pinnae, arise is densely mantled with white, broadly based scales as shown at http://www.backyardnature.net/n/13/130210cj.jpg.

In that picture you can also see the brownish sporangia peeping from inside the leaflets' curled-under margins, in typical lip fern manner.

This is CHEILANTHES HORRIDULA, and despite its species name really I can't find anything horrendous about it. Its hairs aren't stiff enough for the fern to be prickly or unpleasant in any way. Its main English name is Rough Lip Fern. It's yet another endemic species, in the US found only in parts of Texas and a tiny sliver of southern Oklahoma, plus it occurs in arid uplands of northeastern Mexico.

Ecologically one service the Rough Lip Fern performs is that where it roots in limestone cracks, often debris collected around its stems attracts tiny arthropods who shelter there. Then other tiny critters come to prey on the arthropods, and before you know it you have a tiny ecosystem structured around a little fern most folks wouldn't notice.

I'm glad I noticed it, though, because it's a good find, an obscure species not found in many places, a being with genetic information exquisitely fine-tuned for a specific small spot on Earth, and a specific manner of being craving cracked limestone.

*****

WHITE SPLOTCHES ON LIMESTONE ROCKS
Atop sun-baked, windswept, limestone hills framing the valley of the little Dry Frio River flowing behind the cabin, the vegetation becomes sparse -- just a few grasses, cacti and small, spiny shrubs. Atop the hard, Cretaceous-Era Edwards Limestone capping the hills soil is thin to nonexistent, and loose limestone rocks lie about sometimes making it hard to navigate. Often the limestone is splotched with white, crustose lichen, as shown on a car-tire-sized rock at http://www.backyardnature.net/n/13/130210ln.jpg.

From a few steps away those white lichens display no conspicuous field marks to help with identification, but up close they reveal some modest details. One is that in some places the lichen's smooth, white, featureless surface becomes a bit warty and cracked in a halfway systematic manner, as shown at http://www.backyardnature.net/n/13/130210lo.jpg.

In other places small, craterlike openings with black interiors pit the lichen's body, or thallus, as shown at http://www.backyardnature.net/n/13/130210lm.jpg.

The pits are apothecia inside which fungal spores are produced. These apothecia are different from those we've seen lately in other species in that they are much smaller, and sunken into the thallus.

This lichen forming white, roundish spots on exposed limestone, with a smooth body that often cracks like dried mud, and whose surface can become spotted with tiny, black-centered apothecia appears to be ASPICILIA CALCAREA, sometimes called the Calcareous Rimmed Lichen. The species is documented practically worldwide wherever limestone rock exposes itself to the elements. In the US it is much more commonly noted in the arid West than the humid East. It is documented growing on canyon and archeological rock-shelter walls at Amistad National Recreation Area just west of here. In rainy Europe it appears to be common, and much noted on old gravestones. This relative rareness in humid eastern North America but regular appearance in humid Western Europe suggests to me that there may be more than one species involved, but that's a detail for the specialists.

For us it's enough to file pictures on the Internet showing what's growing atop our hills here, placing the pictures in a reasonable pigeonhole until the right researcher comes along. And that pigeonhole, which the search engines will find, catalog and make accessible to the world soon enough, is: Aspicilia calcarea.

*****

MUDROCK
A nice place to visit along the little Dry Frio River flowing behind the cabin is a spot where the water comes right up to a flattish bed of rocks running alongside the stream just above water level. Here you can sit or lie in the sun without insects in the grass bothering you. You can see the spot, with the bicycle I use providing scale, at http://www.backyardnature.net/n/13/130210md.jpg.

The brown, more smoothly surfaced rock closest to the water is shale. The whitish rock layer above the shale and on which the bicycle tires rest looks like a layer of lumpy mud -- except that it's rock hard and sandwiched between other layers of bedrock we know to be of early Cretaceous age. This mud was deposited about 100,000,000 years ago, back when dinosaurs roamed the Earth. In fact, a bit east of here, in northeastern Uvalde County near Utopia, paleontologists have documented dinosaur tracks in similar stone.

The whitish rock the bicycle stands on can be called mudrock. It was deposited as mud but over millions of years it transformed, or "lithified," into rock.

But, the term mudrock is very general and imprecise. According to some estimations, over half of all sedimentary rocks can be called mudrock. Mudrocks are those composed of fine-grained (smaller than sand), silicon-based particles that have broken off other rocks and which were transported and deposited as mud. Such rocks are said to be "siliciclastic," the "silici" referring to silicon -- and over 90% of the Earth's crust is composed of silicate minerals -- and the "clastic" referring to rocks composed of fragments, or "clasts," of pre-existing minerals and rocks.

With technical analysis, mudrocks can be assigned more precise names, such as claystone, mudstone (as opposed to mudrock), siltstone, shale and slate. The categories are defined in terms of the size of the particles of which the mudrock is composed, and the manner in which the rock's structure has altered during the lithification process. A problem with these sub-categories of mudrock is that the experts aren't in agreement on a standard set of criteria, and a standard terminology.

Basically, if you have a sedimentary rock composed of tiny particles smaller than sand, and the source material for the rock was a silicon-based rock or mineral (not a carbonate like limestone), you can pretty safely call it a mudrock. And mudrocks have many appearances. Above we saw mudrock forming flat, even beds. Right above the bicycle the mudrock assumes a different face, becoming much more irregular and heterogonous in content, as shown in the lower half of the picture at http://www.backyardnature.net/n/13/130210mc.jpg.

In that picture, possibly the darker rock above the white mudrock also is mudrock, or maybe it's "lime mudstone"... Fact is, lots of rocks can't be clearly and neatly assigned any specific name everyone would agree on. It's only in human heads where everything must fit into this or that conceptual pigeonhole. Nature doesn't feel at all obliged to limit its creations to humankind's artificial mental categories.

*****

JOINTS IN MUDROCK
In the above picture of the bicycle on the flattish mudrock you may have noticed a straight fracture in the mudrock originating in front of the bicycle and running across the rock in the same direction as the tire. A close-up of the rock break with others beside it, forming a big H occupying most of the picture, is shown at http://www.backyardnature.net/n/13/130210mb.jpg.

These breaks in the rock are not faults, but rather joints, and joints are very commonly seen in a wide variety of rocks and in many geological environments. The difference between a fault and a joint is that faults are fractures where one side of the break slides past the other. Joints are breaks in the rock where little or no "lateral displacement" -- sides sliding past one another -- has taken place.

Joints form in rocks for various reasons. Forces from within the Earth that shift continents around and cause land masses to rise and sink -- tectonic forces -- can warp layers of rock causing them to crack into joints. When hot rocks cool, as when lava from a volcano cools, joints can form as the cooling rocks contract. The most common cause of joints, however, is when erosion removes overlying rocks, thus reducing the weight bearing down on a stratum. This loss of pressure cases the stratum to need to expand, but it's can't, so it buckles and fractures with many joints.

Joints often run predominantly one way or another, depending on the location of the pressures and release points causing the fractures. These alignments are so regular and predictable that sometimes the geologically savvy can use joints as natural compasses plainly visible in the landscape.

*****

FEATURED ESSAYS FROM THE PAST:

"Happiness," from the March 24, 2008 Newsletter, at http://www.backyardnature.net/n/p/080324.htm.

"Thoreau, Chinese Landscape Painting & Bitterness," from the February 2, 2007 Newsletter, at http://www.backyardnature.net/n/p/070202.htm.

 

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.

Visit Jim's backyard nature site at http://www.backyardnature.net