Texas Bull-Nettle

I was out botanizing a vacant lot just a few blocks down from my house recently when I came across a plant that is more than capable of defending itself from potential herbivores or the unwary naturalist.  This is none other than Texas Bull-Nettle or Cnidoscolus texanus.

The white flowers are mostly harmless but the remainder of the plant is loaded with trouble.  With other common names like Bull Nettle, Treadsoftly, and Mala Mujer (I get the direct translation of the Spanish but there must be some cultural context tacked onto this that I am ignorant of–Can anyone place this in the correct context?),  there is no doubt that this plant means business.

These are herbaceous plants, about 80-100cm tall.  An individual plant has separate male and female flowers together on the same inflorescence.  I didn’t get any closer to this plant than I had to so can’t be for sure which sex these flowers are.  The next photo reveals why I kept my distance from this plant.

Notice both the main stem and the stem branches.  All are covered with hispid or bristly hairs. But these are not normal hairs; they are extremely painful, stinging hairs. The leaves are covered with the same stinging hairs as well.  Here is how this plant defense mechanism works: If the foliage or stems are touched, the glass-like hairs break off in the skin (yours or a hapless four-legged fellow creature) and act like hypodermic needles. The “needles” release a toxin which causes an intense burning sensation. This effect is a type of allergic response known as contact urticaria and the reaction can last for several days.

The genus name Cnidoscolus says it all. The Greek cnide means nettle and scolopes means prickle or sting. From the flowering plant family Euphorbiaceae.  A good plant species to know and respect!

A small thought for Earth Day

During my lectures on cell division I tell my plant biology students that if there is only one reason they could ever care about the environment or ecology then they should be concerned about the loss of plant biodiversity, especially in the tropical rainforests. Reason being is that in the medical treatment of cancer we have two main successes, both using chemical compounds produced by plants. Vincristine is used in the treatment of childhood leukemia with good success and Vinblastine has fairly good results with Hodgkin’s Disease.  One came from the Pacific Northwest of the U.S. and the other from a plant in the tropics.  Plants synthesize these compounds for use in defense and they work the same way in the cells of our bodies as they do in the plant cell.  We are not even close to being able to dream up chemical compounds like these in the laboratory.  Maybe in a hundred or two hundred years, just as likely never.  There are other compounds in plants waiting to be discovered in the tropical rainforests that undoubtedly have the same or greater medical potential as Vincristine and Vinblastine.  The problem is that many parts of tropical rainforest are being cleared, sending hundreds of plant species to extinction, never to be examined by humans.  These plant species have never even been given a scientific name.  We are seeing a great potential benefit to humanity being erased from the planet forever.

Just a small thought on Earth Day….

How do yucca moths find yucca flowers in the dark?

If you have read the previous post about how yucca flowers are pollinated by the yucca moth you might wonder how the moth is able to navigate to flowers in the dark.  Well, it’s fairly well known that many insects have visual capabilities outside of the visible portion of the electromagnetic spectrum.  What many people may not be aware of is that many parts of flowers have evolved to take advantage of an insect’s visual range, especially in the UV or ultraviolet part of the spectrum.

It just so happens that Yuccas have “UV-coded” their stamens (male reproductive part of the flower) and especially the anthers, which produce the pollen.  Take a look at the UV photograph below of the stamens from a Yucca flower.  The bright white parts of the stamens are the anthers.

UV photo of Yucca stamens

I would be willing to bet that the yucca moth has  visual capabilities in the UV range and is assisted in its pollination duties by the UV-visual anthers.  Would other insects be drawn in as well?  Maybe.  But there are a couple of things to consider.  First, many insects are not active at night.  Second, yucca flowers do not have nectaries which provide nectar as a reward for transferring pollen to other flowers.  Most insect-pollinated flowers have nectaries to provide a food reward for the insect.   For yucca flowers  the reward or offering to the moth is the flower’s ovules or immature seeds.

Just another interesting aspect of the natural history of Yucca torreyi. Thanks to Monique Reed of Texas A&M University for suggesting this topic and providing the photo.  Photo credit goes to Robert Corbett.

Torrey’s Yucca: great natural history

Torrey’s yucca, Yucca torreyi, is one of two yuccas that we have in our area.   I was out botanizing yesterday south of Abilene (Texas,USA) in Abilene State Park and found a good number of these monocots in full flower.  Torrey’s Yucca is a member of the plant family Agavaceae.  The plant pictured may be a little non-typical in that the panicle inflorescence, which is the entire mass of flowers, is not sitting up higher in comparison to the long leaves.  Typically, the upper half of the panicle of flowers will stand above the top leaves.  However, the length of the sword-like leaves on this particular plant are about 90cm, which is typical of this species.  The other species of yucca found here on the Rolling Plains, Yucca constricta, has leaves no longer than about 65cm. One final supporting morphological feature found on the leaves of this specimen are the narrow threads on the margins.

Below is a close up image of the inflorescence.  Note the large number of pendant or drooping flowers.

Below, a close up of the inside of one flower:

To the best of my knowledge the yuccas (species in the genus Yucca) are endemic only to North America with 35 species total in the genus.  They are found in warm areas and were used extensively by Native Americans as a source of food, fiber, soap, and medicine.  Torrey’s Yucca is named for John Torrey (1796-1873), a distinguished American botanist, physician, and collector of many western North American plants.

Pollination in yuccas is interesting.  All species are dependent on the yucca moth for pollination. Apparently, if the moths are not present Yuccas can reproduce vegetatively (which is a nice evolutionary adaptation to have).  Quoting from Powell (1988):

The yucca moth (Tegeticula = Pronuba) flies at dusk to a flower where she climbs stamens to collect pollen and pack the pollen in a large ball-like mass under her neck.  She then visits another flower where she inserts her ovipositer directly through the ovary wall and deposits 20-30 eggs, one at a time, each directly in to an ovule.  She then climbs  to the stigma of the same flower and spreads the pollen, thus ensuring pollination, subsequent fertilization, and developing seeds that provide nourishment for the moth larvae. Each larva ultimately destroys the seed in which it grows, but there are many undamaged seeds left in the yucca capsule.

From Google a picture of a yucca moth (http://en.wikipedia.org/wiki/Prodoxidae):

A species of yucca moth in the family Prodoxidae

The relationship between the yucca and yucca moth is termed a mutualism,  in a general ecological context.  More specifically, this is a marvelous example of an obligate mutualism for the moth species of the genera Tegeticula, which both pollinates and deposits eggs in Yucca flowers.  For the moth, the relationship to yucca is termed an obligate mutualism because the moth larvae feed only on yucca seeds.  The yucca moth has special mouth parts which allow it to package and transfer the flower pollen. For the yucca plant the relationship is mostly obligate because only yucca moths transfer their pollen between yucca flowers for fertilization.  I say mostly obligate since yuccas can reproduce vegetatively, so they can perpetuate themselves without sexual reproduction.  There are advantages and disadvantages to asexual reproduction.  However, the bottom line for yuccas is that they have coevolved with the yucca moth to form a very unique mutualistic relationship.  Therefore, it’s probably fairly safe to say that sexual reproduction via the yucca moth is most likely the primary means of reproduction for the yucca.  Such a highly evolved relationship with an insect is not happenstance.

The evolutionary history of the other genera of the moth family Prodoxidae is quite fascinating.  A second genus in this moth family, Parategeticula, also has an obligate relationship with yucca flowers as well. Individuals of a third genus of yucca moths, Prodoxus, do not have a mutualistic relationship with yucca plants, neither depositing their eggs in yucca seeds nor moving around pollen from the flowers. However, Prodoxus eggs are deposited in the fruits (mature ovary from a flower) and leaves of yuccas where they eat and grow, which is more of a herbivorous relationship.

Hopefully, I have all of this evolutionary history straight.  I have a huge interest in plant-animal coevolution and, as an evolutionary botanist, delving into a story such as this is like dining at a five-star restaurant (minus the huge bill at the end!).  A reference for those wanting more is the article by  Pellmyr et al. (1996), referenced below.  This is recommended reading for those who find this plant-moth saga as fascinating as I do.

One never knows where an afternoon of botanizing will lead….

References:

Powell, A.M., 1988. Trees and shrubs of Trans-Pecos Texas including Big Bend and Guadalupe Mountains National Parks. Big Bend Natural History Association.

Pellmyr, O., J. N. Thompson, J. Brown, and R. G. Harrison. 1996. Evolution of pollination and mutualism in the yucca moth lineage. American Naturalist. 148: 827–847.

Copyright © Rick L. Hammer 2009

Wavy-leaf Gaura

Wavy-leaf Gaura, Gaura sinuata, with a number of flowers clustered together in the above image.  There are 4 clawed petals (slender stalk at the bottom of the petal), almost standing erect and spaced equally apart (see the flower in the upper right corner), and 8 stamens (male flower parts) hanging down in front.

This is one of several species of Gaura found here in the Rolling Plains and is widespread in Texas. The Flora of the Great Plains describes this particular species of Gaura as “often too common in sandy prairies & open woodlands, stream valleys, roadsides, waste places.” Nevertheless, an attractive part of our local flora.

Greenthread on the Rolling Plains

This might be the second most dominant composit, or member of the sunflower family, that is flowering out here in the western part of north-central Texas.  We are experiencing a very dry spring so I feel lucky to have the few early spring wildflowers that are presently in bloom.  Greenthread, or Thelesperma filifolium, is an annual or short-lived perennial commonly found in prairies, roadsides and disturbed areas.

For those who are not familiar with the floral structure of flowers in the sunflower family the first thing to know is that the above image is actually an entire inflorescence, a collection of about 20-25 flowers.  The yellow “petals” you see along the outside of the flower head are called ray florets and the different-looking florets in the middle of the head are called disk florets.  I really like the reddish-brown color of the disk florets in Greenthread.

The above image shows the plant habit with the linear leaves.  Also notice that the grasses surrounding are colorless, a good confirmation of our state or dryness.  Greenthread occurs in the same habitat as Engelmann’s Daisy (previous post) and the two make a good spring duo.

Engelmann’s Daisy in full bloom

We have a number of wildflowers in bloom on the Rolling Plains but at least in and around Abilene it seems that Engelmann’s Daisy, Engelmannia peristenia, is the most common at this time, followed by Greenthread, Thelesperma filifolium (more on this species later). Engelmann’s Daisy is abundant along Interstate 20 north of Abilene and also in town along the US83/84 freeway. The name for this species that many may be familiar with is Engelmannia pinnatifida (published 1840).  But some enterprising botanists dug up an even older name from the scientific literature that was published in 1832, which is E. peristenia.  In taxonomy the oldest, validly published name takes precedence, even though we don’t sometimes discover these older names until 100s of years later.

I have enjoyed seeing this plant lining the roadsides over the last week.  While out walking among the populations today I could see many plants that have yet to bloom.  So, we should be in for a good stretch of blooms from this species for the next several weeks. Engelmann’s Daisy is supposedly found throughout all of Texas except for the forested sandy areas in the eastern part of the state. According to the Flora of North Central Texas, farmers and ranchers refer to this as an “ice cream” plant because it is preferred by livestock. This is why it is so abundant along highway right-of-ways and not found in areas where grazing animals can get at it.

Engelmann’s Daisy is a member of the sunflower family or Asteraceae.  Here’s a photo which shows the stem and leaves:

In the taxonomy world we call this genus (Engelmannia) a monotypic genus, since it has only one species which is this one. Engelmann’s Daisy is named for Dr. George Engelmann (1809-1884), a German-born botanist and physician of St. Louis.  This attractive plant is native to North America and I think it would look nice  in a cultivated bed.

While out scouting for blooms today I also found Greenthread in flower (Thelesperma filifolium) and Texas Sage (Salvia texana).  Stay tuned.  I have pictures…..

Rolling Plains Residents

This is my first post written from Abilene, TX, in my humble abode just about a block from Hardin-Simmons University (HSU).  I am officially a new Rolling Plains resident. I’ve just finished my third week as a new professor of biology at HSU.   It’s been hectic but enjoyable, and along with my wife having a scheduled major surgery last week (my family still lives 5 hours from Abilene), I’ve been been quite busy to say  the least.  My wife is doing great and along with school duties starting to approach a manageable routine I am hoping to devote more time to the Rolling Plains flora and this blog.

Now on to a Rolling Plains resident of the botanical sort.  During my daily walk into the HSU campus I cross a street that borders the north side of campus.  The north side of the street is bordered with a line of trees in deciduous, leaf-off mode at present.  I’m pretty sure these are pecan-Carya illinoisensis-trees.   But what really drew my attention to them was the numerous and noticeable “shrubs” that were suspended among the leafless branches of the pecan trees.

Most folks probably know that these aerial shrubs are none other than mistletoe or Phoradendron sp. (this is probably Phoradendron tomentosum), which is a hemiparasite. Hemiparasites like mistletoe live on their host for physical support but also insert what is essentially a root or haustorium into the stem tissue of their host.  Being a hemiparasite, as opposed to a strict parasite, means that mistletoes do make at least some of their own food via photosynthesis and extract water and mineral nutrients from their host.  Most photosynthetic plants are green because they contain the green photosynthetic pigment called chlorophyll.  The leaves of mistletoe are definitely green in color.  Here’s a closeup shot of one of the mistletoes:

In the above image note the green leaves and white fruit.  At this time of winter mistletoe can be seen all over town here in Abilene.  From an ecological sense, hemiparasites like mistletoe do take a toll on their host since they are reducing the host’s water and nutrient availability.   If the mistletoe infestation is heavy enough the result could certainly be fatal for the host species.  And aside from ecological and biological implications for the host many residents proabably consider them to be an eyesore that detracts from the “natural” habitat. That being said, I was surprised (after doing a little research)  that mistletoe is generally considered to be of positive ecological importance.

Recent research has shown mistletoe to be a keystone species.  A keystone species is a species that has a disproportionate effect on its environment relative to its abundance (see “Keystone Species” in Wikipedia; or some readable, technical references upon request).  Many animals depend on mistletoe for food, eating the leaves and young shoots and both help transfer pollen between plants and disperse mistletoe’s sticky seeds.  Maybe even more relevant for us here in the Rolling Plains is mistletoe’s interactions with juniper shrubs and trees that are prevalent just to our south.

Quoting from the Wikipedia entry on mistletoe:

A study of mistletoe in junipers concluded that more juniper berries sprout in stands where mistletoe is present, as the mistletoe attracts berry-eating birds which also eat juniper berries; juniper berries that have passed through a bird’s digestive tract are less likely to remain imprisoned within a hardened outer capsule.[see reference below] Such interactions lead to dramatic influences on diversity, as areas with greater mistletoe densities support higher diversities of animals. Thus, rather than being a pest, mistletoe can have a positive effect on biodiversity, providing high quality food and habitat for a broad range of animals in forests and woodlands worldwide.

(source: http://en.wikipedia.org/wiki/Mistletoe); also: Susan Milius, “Mistletoe, of All Things, Helps Juniper Trees” Science News 161.1 (January 2002:6).

One final reference for the mistletoe as a keystone species idea: David M. Watson, “Mistletoe-A Keystone Resource in Forests and Woodlands Worldwide” Annual Review of Ecology and Systematics 32 (2001:219-249).  I can provide access to this for those who would like to dig deeper.

I just may be able to start thinking about mistletoe in a new way.  We’ll see.

Stay tuned for further botanical natural history adventures from the Texas Rolling Plains….

Windflower in bloom

While hiking in an in-town natural area a couple of days ago my son Nathan and I came upon a pleasant surprise–Carolina Anenome or Windflower.

Windflower, or Anenome caroliniana is one of my favorite late winter/early spring wildflowers.  I usually start seeing this plant in flower starting sometime in February but I spotted this plant in a small population of early blooming plants.  This flower has no petals.  The white “petals” are actually sepals, which on a typical flower, are green in color.  These plants are perennials.  This particular species is confined mostly to the eastern 1/4 of Texas.  However, the Rolling Plains should have its own species of Windflower, Anemome berlandieri, and I will be on the lookout for this in the upcoming weeks.

This should be my last post from College Station, TX. Relocation to the Texas Rolling Plains happens soon…

Winter annuals in bloom but probably not on the Rolling Plains (yet)

Chickweed from the family Carypohyllaceae

The above image is the flowerbed/lawn weed commonly called chickweed, or called by its scientific name, Stellaria media.  I took this picture to field test (in my front yard no less!) my new point-and-shoot digital camera (Cannon PowerShot SX10IS) which I purchased especially for taking  just this kind of picture. The image is actually enlarged quite a bit since chickweed flowers are no more than about 4-5 millimeters across.

Does this species actually grow in the Abilene/Rolling Plains area?  Good question.  Since I have not moved to Abilene yet (see the first blog post) I really can’t say if it’s found there.  This shot was taken in the front yard of my home in College Station, TX, which is about one hour NW of Houston.  We have much warmer winters in the College Station area than in Abilene, which is about a 5 hour drive to the NW.  Chickweed is commonly seen in flower around College Station most of the winter into the early spring.  I checked in the Flora of North Central Texas (published by the Botanical Research Institute of Texas, more about this publication later) and this book indicates that chickweed is found over most of Texas.  I’ll be eager to verify this for the Abilene area in a few weeks when I take up residence there.  Even if it’s found around Abilene I’ll bet it’s not in flower at present due to the much colder temperatures they’ve experienced over the last few weeks (one night of 17°F last week).

Finally, a little flower morphology for the chickweed image.  On looking at the pic you might think that there are 10 white petals.  Actually, there are only 5 petals as each petal is bifid or split into two segments towards the top.  The dark brown spots in the middle of the flower are stamens, the male parts of the flower that release pollen.  In the very middle of the flower you notice a three-branched segment.  Each of the three segments is a style with a stigma at the very tip.  The stigmas are where the pollen, hopefully from a different flower, sticks and begins the process of fertilization of the flower’s ovary.

I’ll try to post some images of other common winter annuals soon.  In the meantime please have a Merry Christmas!