Arthraxon hispidus

Earlier this year, September 14th to be exact, while driving a gravel road through a section of the Mark Twain National Forest I noticed a dramatic change in the structure of the roadside vegetation. My brain instantly weighed my desire to stop and investigate against my need to get some real work done. Before I could make up my mind, my foot hit the brake. It always does.

What I had seen was a large colony of grass that superficially resembled Microstegium vimineum in overall stature and habit. However, the inflorescences more closely resembled Bothriochloa bladhii.

Luckily, I had my copy of "Steyermark’s Flora of Missouri" (Yaskievych 1999) riding shotgun. A quick run through the keys gave the name Arthraxon hispidus.

I had heard of this grass before, though I had never seen it. It occurs rather sporadically throughout the eastern U.S. and is more common in the southeast (Kaufman and Kaufman 2007). Vegetatively, it is readily identified by its clasping leaves (similar to Dichanthelium clandestinum) and strongly ciliate leaf margins.

Arthraxon hispidus is native to Japan and Eastern Asia. The first record of its occurrence in the U.S. came from Pennsylvania in 1877 (Yatskievych 1999). As with its gross morphology, it seems to prefer the same habitats as Microstegium vimineum; mesic to wet disturbed sites in open forests and floodplains. The most likely mode of dispersal seems to be from logging equipment and trucks, also similar to Microstegium vimineum. I don’t know that this grass has great potential for invasion in Missouri, but it was dominating the roadside where I found it for 50 or 60 meters and appeared to be spreading into the surrounding pine woodland. This county record represents the fifth county it is known from in Missouri (as of 1999). Regardless, the accumulated effects of several weak invasives can be as detrimental to a local ecosystem as one strong invasive, if not more so. Let's hope it behaves itself.

------------------------------------------------------------------------------------

Kaufman, S.R. and W. Kaufman 2007. Invasive Plants: Guide to identification and the impacts and control of common North American species. Stackpole Books. Mechanicsburg, Pennsylvania.

-------

Yatskievych, G. 1999. Steyermark's Flora of Missouri. Conservation Commission of the State of Missouri. Jefferson City, Missouri.

Pic Picks 2009

Now that the growing season has ended and the 2009 Botany Slideshow Extravaganza is over, I thought I would post some of my favorite photos from the year. The lack of labels or narrative is intentional. If you want a name, hover your cursor over the image and look for the name within the file name. Enjoy!

Rash Doctors

Many of the botanists of yore were primarily medical doctors by profession. Examples include such greats as Asa Gray, George Engelmann, John Torrey and to some extent Carolus Linnaeus himself. If modern doctors had such affection for our wild flora, perhaps I wouldn’t cringe when I commonly hear of people in the Midwest diagnosed with Poison Oak or Poison Sumac rash. To them, I usually reply with some cynically derived question regarding the geographical location of their encounter with the offender. If they have been diagnosed with Poison Oak I ask, “have you been in the forests, woodlands or swamps of the southern states lately?”. My Poison Sumac inquiry is more specific. “Have you been in a high quality wetland community lately?”, I say.

Most folks eye me queerly and retort “no, I was doing yard work” or “whatever do you mean”. The bait being taken, I explain that Poison Ivy is a much more likely explanation for their dermal discomfort; especially for those living outside the range of anything but Poison Ivy, as most Midwesterners are. Some, in true argumentum ad verecundiam fashion, defend their doctor’s claim. Others are interested in the difference and enjoy learning a bit of natural history. For those that don't know the difference.....

...here is Poison Ivy (Toxicodendron radicans).

Notice the sharp pointed teeth on the leaflet margins, the pointed tips of the leaflets and the long petioles of the lateral leaflets. Its habitat ranges from anywhere to everywhere; xeric to mesic, acidic to calcareous, disturbed to pristine, the PI can live there. Poison Ivy usually grows like a true vine. It clambers and twines on structures and other vegetation. It is common throughout North America in every state and province east of the Rockies.

Here are two photos of Poison Oak (Toxicodendron pubescens).

Notice the rounded teeth of the leaflet margins, the blunt tips to the leaflets, the nearly sessile lateral leaflets and the relatively long petiole of the terminal leaflet. Its habitat tends to be quality dry to mesic forest and woodlands. Poison Oak does not vine or climb on other vegetation but rather grows as a small shrub. Its geographic range is basically the southern states of the Civil War with a few stragglers into border states.

Lastly, here is Poison Sumac (Toxicodendron vernix).

Notice that the leaves are entire and pinnate instead of trifoliate –so much for the “leaves of three” adage. The habitat of Poison Sumac consists of quality fens, bogs and wetlands. It grows into a shrub of ten feet or so. It occurs sporadically throughout most of eastern North America.

So the next time the doc says “you have poison oak”, Get a second opinion and get it from a botanist.