Issued from the valley of the Dry Frio River on the
southern slope of the Edwards Plateau, northern
Uvalde County, southwestern Texas, USA

August 18, 2013

Last month we looked at a shallow pool choked with flowering pondweed. During this droughty summer the little Dry Frio River is just a chain of such pools separated by dry stretches of gravel and cobblestones. Now the water in our pondweeds' pool is even lower and wandering cattle have smushed the pondweed and mud together into a soggy mess. Still, the pool harbors untold numbers of tiny frogs that are quite active during hot, dry daylight hours. You can see one at http://www.backyardnature.net/n/13/130818ac.jpg.

That frog is about ¾-inch long (2cm), and besides its smallness and being active during the day, its main field marks are the dark triangle between the eyes, the dark stripes on the back thigh, and the rounded, somewhat long snout.

We've run into this species before. In Mississippi we had a different subspecies, Acris crepitans ssp. crepitans, which was reddish brown, as shown at http://www.backyardnature.net/n/09/090216cf.jpg.

This time last year, here, we ran into our current subspecies, the Blanchard's Cricket Frog, ACRIS CREPITANS ssp. BLANCHARDI, but that one was very pale, almost whitish, as you can see at http://www.backyardnature.net/n/12/120909fg.jpg.

So, there's a lot of variation in this species, and one worries about getting the ID right. However, there just aren't many species that are this small, are active during the day, display the above field marks, and occur in southwestern Texas. The whitish one found last year suggests a Gray Treefrog, but they're larger and bear conspicuous, round toe pads.

Cricket frogs are known to migrate after rains for distances of up to 4/5ths of a mile (1.3km), looking for new ponds. When you see how many occupy the little pools along the Dry Frio you understand why migrating might be a good idea. I guess that most cricket frogs that migrate away from the river simply die, which certainly is one way to lower a pool's population density to sustainable levels.

Over much of their distribution, along with many other amphibian species, cricket frogs are disappearing completely from large areas. I'm thankful that along the Dry Frio, on rare rainy nights, we can still hear the crickety calls of these little beings.


Submerged aquatic vegetation in the Dry Frio River's drying-up pools is heavily coated with the gray-brown, muddy, calcium-carbonate-rich marl we looked at recently. In the same pool in which cricket frogs were so abundant among cow-trampled pondweeds, my attention was drawn to the marl-covered aquatic plants shown at http://www.backyardnature.net/n/13/130818ch.jpg.

At the right in that picture we see a submerged, marl-covered network of fine leaves and stems of the carnivorous Bladderwort we've met at http://www.backyardnature.net/n/h/utricula.htm.

At the picture's left, there's something else. Even so heavily laden with marl we can make out numerous leaves arising from a stem in a whorled pattern -- with many slender blades arising from each stem node. Elsewhere in pools of the Dry Frio we've seen watermillfoil with whorled leaves, as shown at http://www.backyardnature.net/n/h/watermil.htm.

However, the whorls on this aquatic plant are much farther apart than those of watermillfoil. Reaching beneath the water I shook off most of the sprig's marl and got a better view of the plant's form, shown at http://www.backyardnature.net/n/13/130818ci.jpg.

Clearly this isn't watermillfoil. I plucked off a stem tip, scraped off as much marl as possible, and now could see the the strange anatomy exhibited at http://www.backyardnature.net/n/13/130818cj.jpg.

The plant bore no flowers or fruits and I wouldn't have had the slightest idea what it was, except that on ocean beaches I've seen certain algae looking like this. Once I began thinking in terms of "large, freshwater algae" it didn't take long to figure out that this is a green alga member of the genus CHARA in the Stonewort Family, the Characeae. The name stonewort derives from the fact that typically plants in the family live in freshwater in limestone areas throughout the northern temperate zone, where they're often encrusted with calcium and magnesium carbonates. This mineral encrustation makes them feel brittle, gritty, or "stony" to the touch. Numerous Chara species are recognized but I can't distinguish them.

Since Chara species are algae, they bear no flowers or fruits. They reproduce both vegetatively and sexually. Vegetative reproduction takes place by tubers, and special alga structures known as "amylum stars" and "secondary protonema." The sexual organs consist of male "antheridia" and female "archegonia." On our sprig I couldn't find antheridia, but female archegonia were numerous, apparently the male parts having already issued their sperm and fallen from the plant. You can see an archegonium beneath the dissecting scope at http://www.backyardnature.net/n/13/130818ck.jpg.

A new Chara plant can develop from the developing cells in the archegonium.

Ecologically, Chara alga stabilizes bottom sediments, provides food for waterfowl, and cover for fish. It creates habitat for many micro and macro invertebrates, which are important foods for fish, and the alga is consumed by many species of ducks. However, on the Internet more pages can be found selling chemicals to kill Chara than those extolling Chara's virtues. I read that Chara often is called muskgrass or skunkweed because of its foul, musty, almost garlic-like odor, though I smelled nothing, maybe because there was so little of it.

These are primitive plants. Because of their stony covering, throughout evolutionary history they've often preserved well in the fossil record. Paleontologists can recognize extinct relatives of Chara from strata deposited as early as the Devonian Period, over 300 million years ago.


This April on limestone ledges of the nearby Frio River (different from the Dry Frio), we found Mexican Buckeyes, UNGNADIA SPECIOSA. You can see what the tree's pretty flowers and pinnately compound leaves, so like hickory leaves, looked like then at http://www.backyardnature.net/n/w/ungnadia.htm.

On those trees we never got to see the seeds, known as buckeyes. Now our Mexican Buckeyes' capsular fruits are ripe and splitting open, as shown at http://www.backyardnature.net/n/13/130818ug.jpg.

An opened pod with a buckeye seed staring at us appears at http://www.backyardnature.net/n/13/130818ui.jpg.

Seeing the seed's roundness, it's easy to believe old reports of kids using them as marbles.

If you're familiar with Ohio Buckeyes, which also occur here, you can see that the Mexican Buckeye's leathery capsule is shaped differently (not spherical), and that the seed is much smaller. The seed in the picture is 7/16ths inch broad (11mm). The pale tan spot on the blackish seed is the scar left from the umbilical-like "funiculus" connecting the seed to the capsule, and is referred to as the hilum. Buckeye seeds display unusually large, conspicuous hila.

Though the seeds on the ground are eaten by insects and certain small mammals, they're known to contain the toxic alkaloid saponin. Still, Geoffrey Stanford reported in a 1981 issue of "Plant Propagator" {28(2): 5-6} that he and his colleagues ate up to twenty seeds, finding them tasting like pistachio nuts, and suffered no ill effects. However, Stanford followed up by feeding Mexican buckeye seeds to rats, who consequently exhibited signs of both neurological and organ damage, most of them dying within three weeks. Once the rats died, Stanford ended his seed-eating experiment.


Sometimes you meet a plant that's so at home in its environment that the whole setting seems charmed with harmonious presence and grace. The plant seems to glow in a kind of halo as the community around it sings of the ecosystem's perfection. Most often, such moments are fleeting, maybe lasting only as long as sunlight illuminates the plant just right, or maybe as a nearby bird sings its songs.

I had a flash of that feeling the other day when sunlight penetrated a shadowy spot where the little Dry Frio dribbled over a limestone outcrop and ran between boulders, the water orange with tannin from a nearby marsh. The beam of sunlight illuminated the plant shown at http://www.backyardnature.net/n/13/130818lu.jpg.

A close-up showing a flower, unopened buds, and an already pollinated blossom that has lost its petals is at http://www.backyardnature.net/n/13/130818lv.jpg.

In the picture's lower, left corner, note the flower that already has been pollinated, lost its petals, and now bears only green, triangular sepals atop a slender, ribbed, gently arcing ovary. That's an "inferior ovary" because it resides below the sepals, not above them. Most large, simple flowers produce "superior" ovaries above their sepals, so this is a good field mark.

A close-up of the blossom's center reveals more diagnostic features at http://www.backyardnature.net/n/13/130818lw.jpg.

Notice the unusually large, spherical, whitish stigma subtended by eight stamens with their banana-like, pollen-producing anthers atop slender filaments anchored at the style base. Once the flower is pollinated, its petals, style and stigma, and stamens all fall off, leaving the four triangular, green sepals we saw in our first picture, atop the slender ovary. The discarded parts leave interesting scars atop the ovary, as shown at http://www.backyardnature.net/n/13/130818lx.jpg.

Even the leaves and stems of this species are particularly handsome and pleasing to look at, as hinted at by the picture at http://www.backyardnature.net/n/13/130818ly.jpg.

The moment I saw this plant I knew what group, or genus, it belonged to, because in the US Southeast several species of this kind of plant occur, their appearance often suggestive of willow saplings bearing yellow blossoms, and normally living in or close to water. It's the genus Ludwigia, whose species often are known as primrose-willows, water-purslanes, or water-primroses. Primrose-willows belong to the Evening-Primrose Family, the Onagraceae.

About 75 primrose-willow species are known worldwide, with some 31 in North America, and maybe four to be looked for our area. Those four are fairly easy to distinguish. Here, any primrose-willow with slender, willow-like leaves, red stems, and large yellow flowers with four, not five, petals is LUDWIGIA OCTOVALVIS, in books often referred to as the Mexican Primrose-willow.

Despite its Mexican name, this is a remarkably widespread plant, occurring in hot and warm areas nearly worldwide. It's so common in so many places that its original home is uncertain. Judging from the location of species most closely related to it, the best bet is that Mexican Primrose-willow arose in tropical America but then aggressively spread across the planet, probably with the help of humans.

Traditionally Mexican Primrose-willow has been used to treat skin diseases, diarrhea and flatulence. In fact, a 2012 paper by Yakob et al in World Applied Sciences Journal 16 (1): 22-29 suggested the use of Mexican Primrose-willow as an antioxidant as well as a treatment for diseases caused by E. coli.


On a steep, somewhat shaded, lower slope beside the Dry Frio River a certain yellow-flowered member of the Composite or Sunflower Family displayed flowering heads about three inches across (7.5cm). The heads stood atop a stem bearing substantial leaves occurring at stem nodes both singularly and in pairs (both alternate and opposite leaves), as shown at http://www.backyardnature.net/n/13/130818si.jpg.

Back East in late summer and fall several similar species can be encountered, mostly sunflowers in the genus Helianthus, but here it's so arid that it's unusual to encounter such broadleaved, large flowered Composites, and this species stands out. Moreover, when I looked at the involucre below the head, its bracts, or phyllaries, didn't look like those of the sunflowers, as you can see at http://www.backyardnature.net/n/13/130818sj.jpg.

For one thing, most sunflower phyllaries are rough hairy while these are practically hairless, or "glabrous," except for short cilia along the margins. Also, I don't recall seeing sunflower phyllary edges folding downward and "pinching together" like these.

In sunflower heads, only the tiny, cylindrical disc flowers forming the heads' eyes produce fruits -- which we think of sunflower "seeds." The sunflower's petal-like ray flowers -- the ones radiating from the eye -- are "neuter" and produce no fruits. Checking these details on our plant, I bent down one side of a head and found exactly the opposite of what would be found in a sunflower: Ray flowers produced fruits, but disc flowers were sterile.

But before looking at that, you might want to see what our plant's cypsela-type fruit looks like. Having tumbled from the head as I bent down one of its sides, it's at http://www.backyardnature.net/n/13/130818sl.jpg.

That fruit, or cypsela, is thin and flat like a dislodged fingernail. Notice the thin, greenish "wings" on both sides of the dark center, which holds the actual seed. The notch at the top, right is where the base of the ray flower corolla was attached before it fell off after the flower was pollinated. This flat, fingernail-like fruit obviously is very different from sunflower fruits, which people think of as sunflower "seeds." Now locate our wildflower's large, winged, cypsela-type fruit in the head where I bent down one side, at http://www.backyardnature.net/n/13/130818sk.jpg.

Those large fruits we produced only at the flower heads' margins beneath corollas of ray flowers. At the bottom of the cluster of disc flowers forming the head's "eye" you can see where several cylindrical disc-flower corollas have fallen off, leaving behind runty, aborted ovaries that will not develop into fruits.

Only a few genera in the vast Composite or Sunflower Family produce flowering heads in which the disc flowers forming the eye produce no fruits, but the petal-like ray flowers do. Maybe the best known of those that do are the rosinweeds. In fact, our slope-living Composite turns out to be the Starry Rosinweed, SILPHIUM ASTERISCUS, a species occupying much of the eastern US, except for New England; with us the species appears at its southwesternmost point of distribution.

Other rosinweed species can turn up in our area. Among the details distinguishing our plant from those are: its broader leaves whose bases don't grow around, or clasp, the stem; the leaves with either a short petiole or none at all, and; the heads bearing relatively few ray flowers -- mostly 12-17.

The online Flora of North America recognizes five varieties of the Starry Rosinweed. Ours is the typical one, Silphium asteriscus var. asteriscus, whose preferred habitat is described as "Prairies, meadows, open forests, roadsides." The Flora also makes clear that there's been a great deal of confusion about rosinweed names, and maybe there still is. In your wildflower book Starry Rosinweed may go by another name.

Classical literature sometimes refers to a famous Silphium plant producing a resin serving as a rich seasoning and a powerful medicine. That Silphium was a different plant, however, probably of the genus Ferula, maybe a "giant fennel." Stems of some of our rosinweed species of the genus Silphium also exude a bit a resin, which accounts for Linnaeus in 1753 naming the genus Silphium after the classic plant, but our Starry Silphium doesn't seem to produce resin.


If you were with me during the Yucatan years you remember the pleasure morning-glory vines gave us -- such an amazing diversity with so many colors, leaf shapes, sizes and habits. Here the wiry, arid-land Texas Bindweed grows on many fences, but really it's too dry for most Morning-Glory Family members. So, I was tickled this week to find a second morning-glory here, a pretty, purple-flowered one draped on a bush at the woods edge along the river, with leaves distinctively lobed at their bases, as shown at http://www.backyardnature.net/n/13/130818ip.jpg.

Peeping into the flower's throat you see a ± spherical stigma atop a slender style surrounded below by pollen-producing anthers held at different levels, shown at http://www.backyardnature.net/n/13/130818iq.jpg.

The roundish stigma points us toward the genus Ipomoea, a big genus, the most important species of which is the Sweet Potato. Embracing about 500 species, the many species of Ipomoea can be a challenge to distinguish.

In the Morning-Glory Family, the Convolvulaceae, often details of the calyx and its sepals are important to notice. You can see that this species' calyx bears long, spreading hairs, and that the sharp sepals are nearly of the same length -- many species bear sepals of conspicuously different lengths, at http://www.backyardnature.net/n/13/130818ir.jpg.

Our pretty vine is IPOMOEA CORDATOTRILOBA, often called Tie Vine or Purple Bindweed because it's a vine with stems tough enough to tie things together with.

Tie Vine occurs throughout much of the tropical and subtropical Americas, extending into the US into the southeastern Gulf Coast states and a little beyond.


In last April 21st's Newsletter we looked at the Green Milkweed Vine's little green flowers ornamented with arabesque patterns and heart-shaped leaves. These are shown at http://www.backyardnature.net/n/h/matelea.htm.

Now those vines are producing an unusual-looking, pod-type fruit, as shown at http://www.backyardnature.net/n/13/130818ma.jpg.

The spines are so soft that they don't scratch or prick at all. When the pods open, dark, flat seeds bearing feathery, white "parachutes" are released into the wind, just as happens with regular milkweeds along roads and in fields.


Most but certainly not all fern species occupy moist habitats; our edge-of-desert location is better for finding cacti than ferns. Therefore, it's a happy time when a new-for-me fern species turn up at this location. The species encountered this week was a robust, knee-high one with numerous fronds emerging from a moist crevice in the Dry Frio River's limestone bed, as shown at http://www.backyardnature.net/n/13/130818mf.jpg.

Notice how the fronds' subdivisions, or pinnae, are toothed along their margins, and how each frond's lowest pair of pinnae is smaller than the pinnae above it, and that the lower pinnae point backwards. These features are just like those of the most common fern on bayou walls back in Mississippi, the Southern Shield-Fern, which you can see at http://www.backyardnature.net/n/h/shield-f.htm.

However, that fern needs a moister climate, its westernmost point of distribution being humid eastern Texas. Southern Shield-Ferns don't make this far west.

Southern Shield-Ferns are members of the genus Thelypteris, so I figured that this week's fern also was a Thelypteris. Thelypteris ferns are beautiful and interesting but they can be hard to identify to species level. About 875 species are recognized, occurring nearly worldwide, with 21 found naturally in North America. I had problems distinguishing Thelypteris species until I learned the secret of "earmark veins." Therefore, this week as soon as I thought I might have a new Thelypteris, I looked for those earmark veins. You can see them at http://www.backyardnature.net/n/13/130818mg.jpg.

In that picture the tiny, spherical, dark, spore-bearing bags called sporangia also show up, scattered in loose groups on the pinnae undersides.

The "earmark veins" are the two veins forking off the bottom of each pinna's midvein. Notice that the very lowest vein terminates a little above the bottom of a neighboring sinus, while the second-lowest vein terminates at the very bottom of the other sinus. These are the earmark veins. In many Thelypteris species the earmark veins merge below the sinus to form a new vein that shoots upward to the sinus base. In other species, both earmark veins connect with the sinus well above the sinus's base. Sometimes two Thelypteris species will be almost identical, but their earmark veins can behave very differently.

Our Thelypteris turns out to be THELYPTERIS OVATA, often referred to as the Ovate Maiden Fern. The species is widely distributed from Belize and Guatemala north through Mexico and the Caribbean area, and extends into the US in Florida and nearby Coastal Plain zones from South Carolina to Alabama, and also here in southwestern Texas. The US's Florida populations are recognized as the variety ovata, while our Texas ones are variety lindheimeri; sometimes ours are called Lindheimer's Maiden Fern. The Lindheimer's habitat is described as "riverbanks and moist canyons," which is close enough to where ours was found.

So, this is a good find, not only because it's a very pretty species in an area with few ferns, but also because it's always a pleasure to find subtle "variations on a theme." The Lindheimer's Maiden is very similar looking to the US Southeast's Southern Shield-Fern, yet the two species have different habitat preferences, and their earmark veins are ever so slightly differently configured.



"Alive on the Beach," from the May 1, 2011 Newsletter, at http://www.backyardnature.net/n/p/110501.htm

"At the Ocean's Edge" from the February 6, 2005 Newsletter, at http://www.backyardnature.net/n/p/050206.htm


Best wishes to all Newsletter readers,


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