April 13, 2014
A good place to look for rare plants is on very thin soil atop bedrock. Such soil typically is so dry and features such a high or low pH that only plants specially adapted to such conditions can survive in it. That's why I make a point of regularly visiting the top of our hill such soil accumulates in patches atop hard Edwards Limestone bedrock. You can see one of the hilltop's tub-size depressions where some highly calcareous soil has gathered at http://www.backyardnature.net/n/14/140413vw.jpg.
This week the little depression hosts the pink-blossomed, foot-tall wildflower shown at http://www.backyardnature.net/n/14/140413gi.jpg.
I'd never seen anything like this. For one thing, the flowering head, or inflorescence, is curious, the individual flowers on crooked necks atop very long stalks, or pedicels, the pedicels seeming to issue from where small bracts or modified leaves attach to the stems. This is not the normal spike, raceme or panicle configuration of most inflorescences.
Also, up close, the flowers, only about a third of an inch across (8mm), at first glance appeared very typical, with five sepals, five petals, five stamens, and a spherical, superior ovary topped with a style with three stigmas, as shown at http://www.backyardnature.net/n/14/140413gj.jpg.
The first noteworthy feature was that the corolla comes off in one piece -- so the petals are attached to one another at their bases -- which is important to notice because the petals of many species are completely separate from one another and fall off one at a time. Also, the stamens, instead of arising separately from beneath the ovary, are attached to the corolla's short tube. A dissected corolla showing all this is at http://www.backyardnature.net/n/14/140413gm.jpg.
Such a configuration, though important to notice, isn't rare. However, the ovary left when the corolla fell off was more interesting. One is shown nestled in its calyx at http://www.backyardnature.net/n/14/140413gk.jpg.
Ovaries typical for this kind of 5-5-5 blossom are partitioned inside with five or no pie-slice-shaped sections, or carpels. This ovary has three, which is hard to determine unless you study it closely. Notice the three fissures converging at the ovary's top.
At this point it seemed that our plant might belong to a handful of families, especially maybe the Primrose Family. But then I noticed the leaves, one of which is shown at http://www.backyardnature.net/n/14/140413gl.jpg.
Such a pinnately divided leaf with leaflets bearing sharp teeth just don't belong on any plant in the plant families I'm familiar with. This plant turned out to be hard to identify. However, in the end, by noting such technical features as how the ovules were arranged inside the ovary, the little beauty's name was revealed.
It's the Split-leaf Gilia, GILIASTRUM INCISUM, a member of the Phlox Family, the Polemoniaceae. I thought I knew the Phlox Family, for we all know what phlox look like, but now it's apparent that the family is more diverse than I thought. The "Gilia" in our plant's name comes from the plant's history of being assigned to the genus Gilia, before it was shifted to Giliastrum. The genus Gilia was named for a Spanish botanist of the late 1700s.
Is this a rare plant? Not terribly so, though it's certainly not a weed. It's found mostly in rocky and gravelly areas with silty or sandy soils, and is distributed mostly in arid northern Mexico, extending into the US only as far as southern Texas and southeastern New Mexico.
Even though it's not particularly rare, in such an austere, sun-baked, wind-swept environment as the thin soil atop our limestone hill, it's good to see the fragile little Split-leaf Gilia seeming very much at home.
Only a foot or so from the Split-leaf Gilia, from a crack in the hard Edwards Limestone, grew the smaller, even more delicate-looking plant shown at http://www.backyardnature.net/n/14/140413ar.jpg.
Interestingly, this plant isn't closely related to the Gilia, yet also its flowers are diffused throughout an inflorescence seemingly much too large for its tiny stems and leaves. Also, as with the Gilia, its blossoms stand at the tips of long stems, or pedicels. I'm guessing that in such wind-swept habitats where decent soil only spottily occurs, flowers disposed in this manner are better able to disperse their seeds over longer distances. I can visualize on windy days the inflorescences being knocked back and forth causing the split-open capsular fruits atop their long, limber pedicels to toss seeds in every direction.
You can see its opposite leaves (two per stem node) and basal leaves at http://www.backyardnature.net/n/14/140413at.jpg.
A close-up of one of its flowers, only about 1/8th inchhigh (3mm), is at http://www.backyardnature.net/n/14/140413as.jpg.
With its opposite leaves and flower structure, you might guess that this little plant is closely related to chickweed, dianthus and campion, which it is. It's the Hilly Sandwort, ARENARIA BENTHAMII, like chickweed and the others a member of the Pink Family, the Caryophyllaceae. It's endemic to a couple of states in arid northeastern Mexico, but mostly in southwestern and central Texas, and spottily in New Mexico, Oklahoma and Louisiana. Its habitat is described as "Open woodlands, limestone slopes and outcrops," so it's comfortably at home atop our limestone hill.
I read that the various sandwort species traditionally have been used as medicine to treat kidney stones. Plants growing in cracks in rocks often are similarly used, based on the ancient Doctrine of Signatures. That concept suggests that plants "sign" to people what their "purposes" are, so by growing in rock cracks, sandworts "sign" their usefulness in crushing stones, such as kidney stones. I suspect that the Doctrine of Signatures has made life miserable for a lot of people and killed quite a few.
A MALLOW, OF THE MALLOW FAMILY
Especially in Mexico we've seen many species belonging to what books often call the Mallow Family, the Malvaceae, but which I tend to call the Hibiscus Family, since most North Americans don't know what a mallow is. The mallow genus, Malva, is native to Eurasia and Africa, which explains why most Americans don't know it.
Still, one of the most rampant, vigorous weeds in certain disturbed spots around Uvalde is a mallow -- an invasive species from the Old World -- the one shown at http://www.backyardnature.net/n/14/140413hb.jpg.
The leaves on that plant look a bit like those of hollyhocks and the Rose of Sharon, which makes sense, because those species also are member of the big Malvaceae, along with such famous plants as cotton and of course hibiscuses. A better look at a leaf is at http://www.backyardnature.net/n/14/140413he.jpg.
Happily, flowers in the Hibiscus Family are easy to recognize. You can see our Uvalde mallow's blossom at http://www.backyardnature.net/n/14/140413hd.jpg.
Note that in the flower's center the numerous stamens join at the bases of their filaments to form a cylinder, which surrounds the slender style connecting the hidden ovary with its stigmas nestled among the stamens' bunch of anthers. When you see such a "staminal column," think "Hibiscus Family."
Fruits of species in the Hibiscus Family come in a variety of forms. One common type is produced by our mallow, shown at http://www.backyardnature.net/n/14/140413hc.jpg.
Technically, this kind of fruit is known as a "schizocarp," a schizocarp being a dry fruit that at maturity splits into sections known as "mericarps." Mericarps can contain one to several seeds. The intact schizocarps of our Uvalde weed-mallow reminds enough people of a sliced wheel of cheese that probably our plant is best known by the names of Cheeseweed and Cheeseweed Mallow. It's MALVA PARVIFLORA, the "parvi" in parviflora meaning "small," pointing to the fact that Cheeseweed's corollas are small compared to those of closely related mallows.
Cheeseweed's leaves don't have much of a flavor but they can be mixed with other greens and cooked in a pot. The ancient Greeks are said to have made a green sauce with Cheeseweed leaves, and used them as a substitute for grape leaves when making the stuffed vegetable dishes called dolmas.
Native to Eurasia and northern Africa, Cheeseweed now invades weedy areas throughout the warmer parts of the world. In the US it's found mostly in the southwestern states, though it turns up here and there in other states.
In mud along the banks of the little Leona River coursing through Memorial Park in Uvalde, a grasslike sedge flowered handsomely in afternoon sunlight. You can see its classic sedge form at http://www.backyardnature.net/n/14/140413cx.jpg.
True sedges like this plant are members of the genus Carex, of the Sedge Family, the Cyperaceae. However, about 2000 Carex species are recognized, and the online Flora of North America treats 480 species for North America -- with about 74 of those growing in Texas -- so usually when you find a sedge, figuring out which sedge it is can be challenging.
This sedge offered some very distinctive field marks however. You can begin seeing them in a close-up of a head displaying some of the basic features making a sedge and sedge at http://www.backyardnature.net/n/14/140413cy.jpg.
Sedges are such unique beings that to talk about them you need several special sedge terms. In fact, there's a special name for the study of sedges, which is "caricology."
In the above picture you see three spikes at the tip of a flowering stem, each spike bearing several unisexual flowers of both sexes. All three spikes have the male flowers below the female ones, a condition said to be "gynecandrous." Most sedge species don't produce gynecandrous spikes, so noticing this is a big help.
In the spikes, the male flowers have slender, yellowish anthers dangling from them while female flowers consist of a scale, or bract, arising below a green, frying-pan-shaped item, the "perigynium," with an elongate, sharp "beak" pointing upward. Looking closely at the perigynium, you see important features helping us zero in on the species, as seen at http://www.backyardnature.net/n/14/140413cz.jpg.
Here you can see that inside the perigynium a darkened area. That's a hard, dry, one-seeded, non-splitting achene-type fruit or nut. Perignyia, then, aren't fruits, but rather bladder-like coverings of fruits. And perignyia come in a bewildering variety of different shapes and sizes. In fact, to identify a sedge to species level you simply have to pay close attention toits perignyia. Important to note about our sedge's perigynium is that it's flattened, not rounded, and its beak consists of two sharp teeth, not three. Only a minority of sedge species share these traits, so once again these are important field marks.
Other field marks leading us to the exact species include the fact that the hairless perigynium is about 6mm wide, it's more or less spherical or even wider than long, its sides bear conspicuous, papery "wings," and its flat faces bear no clearly visible veins.
All this brings us to CAREX TETRASTACHYA, often known as Britton's Sedge because earlier its binomial was given as Carex brittoniana.
A 2010 publication of the Nueces River Authority, a field guide to riparian plants within the Nueces River Basin, informs us that of Texas's 74 sedge species only six occur in the Rio Grande Plains and the lower Nueces Basin, and that the Britton's Sedge is one of those -- in fact, it's the one species the guide illustrates, as an example of a sedge.
Though apparently common in our area, Britton Sedge is endemic only to Texas, Oklahoma, and a tiny part of Louisiana. It's to be found in moist prairies, shores, banks and roadside ditches. As the season develops, the sedge's perignyia inflate, the spikes increase in size, and begin looking like the spiky, green fruiting heads of Sweetgum trees.
In the tropics a plantain is like a big banana, but in North America the word plantain refers to a certain kind of humble weed typically growing along sidewalks and in abandoned lots. Our North American plantains belong to the genus Plantago. The other day a plantain at the edge of a parking lot in Uvalde caught my attention. It's shown at http://www.backyardnature.net/n/14/140413pl.jpg.
Typical of the genus Plantago, this plant produces greenish, cylindrical spikes of obscure flowers. The flowers' calyxes are greenish and fairly typical looking, but plantain corollas tend to be somewhat papery and maybe stiff, and this species' remain stiffly erect, not opening like the corollas of most plants. You can see some of this plantain's flowers close-up at http://www.backyardnature.net/n/14/140413pm.jpg.
It wasn't the flowers that caught my attention, though, but rather the leaves, shown at http://www.backyardnature.net/n/14/140413pn.jpg.
Though having the major veins arising at the blade base and continuing more or less parallel with one another through the rest of the blade is typical, and I've know several hairy species, I'm not accustomed to seeing plantain leaves with "teeth" or small, narrow lobes along their margins, as these blades have.
This is the Redseed Plantain, also called Redseed Indianwheat, PLANTAGO RHODOSPERMA. Unlike some our most common weedy plantains, who are invasive from Eurasia, this species is native American, occurring mostly in the south-central states from southern Nebraska south through our area, New Mexico and Arizona into the northern half of Mexico.
I've read that chewing the leaves into a pulp, you an make a poultice that helps if you apply it to a fire ant bite or cut.
In the cobblestone-strewn floodplain of the upper Dry Frio I came upon the limestone rock shown at http://www.backyardnature.net/n/14/140413tu.jpg.
Without lab analysis you can't ever know for sure a loose rock's geological age, because it might have come from anywhere. However, being found where it was, it was surely early Cretaceous, like all the limestone bedrock in the area, so the fossils in the rock are remnants of animals that lived about 110 million years ago. The rock contains many fossils and fossil fragments, but a close-up of the three most conspicuous is seen at http://www.backyardnature.net/n/14/140413tv.jpg.
The rock has broken or eroded so that nice longitudinal sections are provided of the ancient animals' shells. It's as if we had cut the shells down their centers, end to end, enabling us to see how the shells' "whorls" spiral around the interior column-like "columellae" (singular columella). The shell is similar to some found on beaches in the Yucatan, so we know that the whorls end at an opening at the bottom of the shell, called the "aperture," through which the animal's soft body extends when it's not drawn into the shell for protection.
Animals with shells like this are mollusks, and mollusks whose soft bodies extend through an aperture at the shell's bottom are gastropods. Snails are the most familiar gastropods.
In my little Golden Nature Guide to fossils the shell most resembling ours is a gastropod known as Turritella. Turritellas, which in geologic time have lived from the Cretaceous to the present, are described as "... slender, high-spired shells with incised sutures and with spiral or transverse ornament."
By "incised sutures," is meant that between the spire's whorls the point of contact is a bit indented. The words "with spiral or transverse ornament," sent me looking with the hand lens to see what's shown at http://www.backyardnature.net/n/14/140413tw.jpg.
The top of that picture is occupied by limestone rock, in which the fossils are embedded. The two dark areas are cavities within one of the fossil shell's two whorls. You can see two "incised sutures" between the two whorls, plus between each incised suture the shell's surface where it makes contact with the limestone bears many small points. Each point is a cross section of a slender ridge spiraling across the shell's surface.These spiraling fine ridges are the "spiral or transverse ornament," and they are a feature of Turritella shells.
My little Golden Nature Guide, though wonderful, is mainly a child's book, so to firm up the identification I submitted pictures to the identification section of TheFossilForum.Com.
In a few hours Herb in Kentucky wrote, "They appear to be Turritella," and that tickled me. A few hours later, though, Erose in Texas added, "Cerithium would be another suspect," so now the issue wasn't as certain as I'd hoped. Not long after, Herb in Kentucky agreed, writing "another possibility also. Hard to say as they have been massively recrystalized."
Both Turritella and Cerithium are often found as fossils in rocks, and species of the genera still roam the ocean floor. However, after viewing many pictures on the Internet of both genera, to me the shells in our rock are much more like Turritella than Cerithium.
So, that's how I'm filing this entry on the Internet: as TURRITELLA, in early Cretaceous rocks either of the Edwards Limestone or Glen Rose Formations.
Turritellas often are called Tower Shells.
FEATURED ESSAYS FROM THE PAST:
"Knowledge is Sacred" from the February 11, 2008 Newsletter, at http://www.backyardnature.net/n/p/080211.htm
"Siesta" from the April 17, 2011 Newsletter, at http://www.backyardnature.net/n/p/110417.htm
Best wishes to all Newsletter readers,
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