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

January 20, 2013

DAPHNIA
A sure sign of spring is that in stagnate pools along the little Dry Frio River behind the cabin pale little specks are appearing jerkily coursing through the clear water. There must be several kinds of organisms involved, but they're fast and hard to suck into the hollow vulture-feather quill I'm using until I can find a pipette or medicine dropper. I did manage to capture one speck, however, which when flushed onto the microscope slide looked a little smaller than a grain of salt. You can see what the critter looked like at high magnification at http://www.backyardnature.net/n/13/130120da.jpg.

That's one of the commonest, best known and easily recognizable of microscopic animals likely to be found in natural bodies of water nearly worldwide. Often it's called a water flea, but some folks call any tiny, erratically moving thing in water by that name. A more informative name is Daphnia, which is the genus name. About 150 species of Daphnia are recognized, living in very many habitats, not only freshwater ones but also very acidic and saline ones. I can't say which species ours is. I think ours had a sharp tail that broke off.

Our Daphnia was unhappy to be on a microscope slide and tried to swim away by beating its antler-like appendages like oars. The dark spot in the head area looking like eyes are indeed compound eyes, like those of an insect. Inside the transparent body, note the dark, baglike area almost touching the back, just above the broken-off tail. That dark area is the brood pouch.

In the spring normally only female Daphnia are encountered. Without the benefit of sex these females parthenogenetically give birth to other females, who similarly will give sexless birth only to more females. These repeating generations of females will continue until cold weather returns or other harsh conditions develop, when males will appear, sex take place, and eggs for the next generation will be produced.

From the moment it emerges from its egg it takes a Daphnia about two weeks to reach adulthood. Under ideal conditions a mature female can produce a new brood about every ten days so, doing the math, it's clear that the life expectancy of a Daphnia is not great, else we'd be knee deep in Daphnia. Lots of small aquatic animals eat Daphnias. In fact, Daphnias are such excellent fare that among aquarists the most popular live food for aquarium fishes is Daphnia. Daphnia themselves eat algae, bacteria, decaying organic matter and such.

Daphnia are crustaceans, along with crabs, lobsters, crayfish, shrimp and barnacles. All crustaceans are encased in exoskeletons, from which they must periodically molt in order to grow.

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RUE OF THE MOUNTAINS FLOWERING
Yet a second wildflower blossoming here in mid January is the wiry, woody-based, foot-tall shrub with tiny yellow blossoms at some of its branch tips shown at http://www.backyardnature.net/n/13/130120th.jpg.

A close-up of one of its emerging flower clusters, or inflorescences, showing the stem, leaves calyx and corolla all dotted with glands appears at http://www.backyardnature.net/n/13/130120ti.jpg.

A broken-open blossom with one side of the 1/8th inch long (3mm), yellow corolla removed and showing that even the ovary is glandular is at http://www.backyardnature.net/n/13/130120tj.jpg.

With my foggy vision, in the field I couldn't see the flowers and figured that this plant was something like the yellow-flowered, stiff-branched Scotch Broom we met in Oregon, a member of the Bean Family. However, the moment the above flower pictures came onto the screen it was clear that there's nothing beanlike to this plant. Few plant families can be so glandular. The foliage was strongly aromatic, too. Immediately the Citrus Family, the Rutaceae, came to mind, the family of oranges and grapefruits, but also of some interesting and often medicinal native plants.

Guessing that it was a member of the Citrus Family, on the Internet it was easy enough to figure out that what we have is THAMNOSMA TEXANA, truly a member of the Citrus Family. In this area most people seem to call it Dutchman's Breeches because of the shape of its fruits, but in eastern North America a famous spring wildflower already is known by that name. Our plant also goes by the names Blisterweed, Texas Desert-Rue, and Rue of the Mountains. The name Texas Desert-Rue ignores the fact that the plant also occurs in arid northern Mexico and other southwestern desert states as far north as Colorado, so here we'll go with Rue of the Mountains. It is described as growing mainly in thin soil atop limestone, which is exactly where our plant occurred, on a limestone outcrop beside the Dry Frio River.

In Mexico we've often run into the "real Rue," which is an important medicinal herb, as described at http://www.backyardnature.net/mexnat/rue.htm.

On that page also you can see that "real Rue" produces small, yellow flowers and is heavily invested with glands filled with fragrant oils, just like our Rue of the Mountains.

Rue of the Mountains contains a toxic compound known as furocoumarin, which induces the interesting medical condition known as photosensitization. Humans avoid the plant, but a study of sheep who ate dried Rue of the Mountains reported increased body temperature in the sheep, avoidance of light (photophobia), swelling caused by fluid accumulation (edema) of the muzzle, ears, and vulva, a general dermatitis, and an eye problem called keratoconjunctivitis. These symptoms suggest why a plant would evolve containing phototoxic compounds: To make it unpleasant for animals to eat it!

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SAWGRASS
In the center of a shallow, stagnate pool beside the little Dry Frio River below the cabin there stands photogenically a clump-forming, grasslike plant lifting its old fruiting heads well above one's head, as shown at http://www.backyardnature.net/n/13/130120sc.jpg.

A close-up of a dried-up, mostly spent fruiting head is shown at http://www.backyardnature.net/n/13/130120sd.jpg.

Small, seed-eating birds such as sparrows and finches have eaten nearly all of what must have been thousands of the heads' tiny, achene-type fruits, but if you look closely you can still find a few grains such as those shown at http://www.backyardnature.net/n/13/130120se.jpg.

The inset at the upper right shows an achene with its enclosing scales removed, revealing two hairlike "bristles" curving from the achene's base over its rounded surface toward its tip. The scale at the bottom of the inset shows that the achene minus its beak is about 2.3mm long (3/32nds inch).

Seeing the oval achenes with their enclosing scales, it's clear that here we're not dealing with a grass. Achenes of members of the Grass Family are subtended by specialized scales called glumes, lemmas and paleas, which are not in evidence here. This graceful and interesting plant is a member of the Sedge Family, the Cyperaceae, and it's called Sawgrass. In Texas, botanists tend to refer to it as CLADIUM MARISCUS, but the Flora of North America lumps our plants with the Sawgrass we had in the Yucatan, Cladium jamaicense.

Whichever name you use, the great thing about this Sawgrass is that it has a tremendous rooting system that holds the banks and streambeds it occupies in place. Also, the big plants themselves slows flooding water, protecting things downstream from rampaging water. With the anti-erosion service and the way small birds relish the thousands of achene-type fruits it produces, Sawgrass is a valuable citizen here.

This Sawgrass species occurs in coastal counties along the US Gulf Coast, then through Texas to southern New Mexico, then south, as Cladium jamaicense, to northern South America.

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SHIELD LICHEN
Probably the most abundant and conspicuous lichen here -- a foliose one commonly seen encrusting the bark of tree limbs, fallen twigs, and sometimes even open ground next to roads -- is the one shown at http://www.backyardnature.net/n/13/130120li.jpg.

That's PUNCTELIA BOLLIANA, sometimes referred to as the Eastern Speckled Shield Lichen. The species is distributed in the central US from here in southwestern Texas north to North Dakota, is absent from most of the US Southeast, but present in the Appalachians and most northeastern states and adjacent Canada. The term "shield lichen" is applied to numerous foliose lichens with the general appearance of this one.

An important field mark for the Eastern Speckled Shield Lichen is the presence of many large, bowl-shaped growths scattered across the lichen's body, or thallus, with brown inner surfaces. These structures are apothecia. A side view of some apothecia displaying their bowl shape is at http://www.backyardnature.net/n/13/130120lj.jpg.

Apothecia are reproductive structures produced by the fungal component of the lichen, and of course lichens are "composite organisms" composed of a fungus and an alga and/or a cyanobacterium. The apothecium's inner surface is covered with innumerable, microscopic, tubelike affairs called asci (singular ascus) stacked next to one another and containing spores (ascospores), which escape from the tubes' tops. When the fungal spores land in a good spot they germinate, their mycelium wrap around an appropriate alga or cyanobacterium cell, and begin growing into a lichen.

Having access to a microscope, I wondered if I could see the layer of asci covering the interior surface of one of this lichen's apothecia. Maybe I could have with the proper slide-preparation equipment, but with just a knife and tweezers I couldn't because the ascus layer was so exceedingly thin. However, while fiddling with the lichen I noticed that its flat thallus surface was heavily speckled with microscopic, dark dots, as shown at http://www.backyardnature.net/n/13/130120lk.jpg.

These black dots must be the speckles making this a speckled shield lichen. A little browsing on the internet revealed what the speckles were.

They're pycnidia -- singular pycnidium. Pycnidia normally are tiny, spherical or upside-down-pear-shaped (obpyriform) structures, partly or entirely sunk into the lichen's thallus, with their internal cavities lined with conidiophores, which are tips of the fungus's hyphae. The ends of these conidiophores break off forming dustlike specks, or "pycnidiospores," which then escape from the pycnidium through an opening in the pycnidium's top. A pycnidiospore can help the lichen reproduce sexually by acting as a male germ cell that unites with a female germ cell to start a new fungus, or it can accomplish asexual reproduction by landing somewhere where it can germinate a hypha that will combine with appropriate alga and/or a cyanobacterium cells and grow into a new lichen. It's as if your fingertip should break off and grow into a full-size copy of you.

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DIATOM GARDENS
Not long ago when the microscope first became available I was interested to find that our little Dry Frio River behind the cabin was home to a species of diatom -- a kind of alga encased within a cell wall made of silica, which is hydrated silicon dioxide.

Now I'm discovering that actually there's an amazing number and diversity of diatoms in the Dry Frio's waters, and that each drop of water I look at turns out to be a veritable diatom garden.

Most diatom species turn up again and again, but regularly spectacular new kinds come to light structured or behaving in ways completely new to me, and mind-boggling to behold. For example, the other day I looked at a rice-grain-size shred of Sycamore leaf that had been decaying in a stagnate pool beside the river and at the tip of a tiny leaf vein extending from the margin of the disintegrating blade I saw what's shown at http://www.backyardnature.net/n/13/130120dt.jpg.

The diatoms are those crystal-like, straight, thin items radiating from the very tip of the vein. The longer, thicker items with crosswalls are filamentous algae and cyanobacteria, so you can see that the crystal-like needles are even thinner than they.

At the Diatoms of the United States website at http://westerndiatoms.colorado.edu I found no pictures of diatoms exactly like ours, but after several days of sporadic web browsing finally I found images that more or less matched, though they were not from this part of the world.

The diatoms in our picture appear to be the genus SYNEDRA, a rather obscure and seldom documented diatom, despite being abundant at this time in the Dry Frio's waters. Little information is available about Synedra, except that one description says that "Several cells can be found clumped together at one pole with a pad of mucilage," exactly as in our picture.

We're in a part of the world where species endemism is great and little attention has been given to matters such as local diatoms, so it's not unreasonable to think we could possibly even have a new species, so maybe someday a diatom specialist will be happy to see our picture here.

The Diatoms of the United States website recognizes nine categories of diatoms. Synedra is in the Araphid group, the third diatom type we've encountered in the Dry Frio.

What a delight to find such unexpected gardens so nearby, even here in the heart of winter.

*****

FEATURED ESSAYS FROM THE PAST:

"Charles's Choir," from the June 9, 2002 Newsletter, at http://www.backyardnature.net/n/p/020609.htm

"Rat & Cat, Sea & Me," from the August 28, 2011 Newsletter, at http://www.backyardnature.net/n/p/110828.htm

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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