Fight or Flight on the Shortgrass Prairie
The area receives an average of 12 inches of precipitation annually. These arid conditions have resulted in a significant percentage of annuals in the flora. Cryptantha crassisepala (photo below) is a fine example. The hairs of the inflorescence are very stiff and are quite pleasing to the touch. With its numerous scorpioid cymes the plant is visually pleasing as well. In the very center of the photo is the final flower of what would have earlier been a much prettier display.
Here on the Great Plains, as with much of Earth's surface, anthropogenic disturbance has significantly altered the ecological integrity of the presettlement natural communities and dramatically changed the natural distribution of plants and animals. Exotic species that are more tolerant of excessive disturbances in biotic and abiotic structure now thrive. Native plants that evolved into the biotic components of the Shortgrass Prairie system were once numerous and well distributed. However, cheap beef to feed a growing nation justified unrestrained grazing. Within a few decades little more than Sagebrush, Tumbleweeds, dust and cowpies were left on the lonesome prairie.
Sadly, the Tumbleweed (Salsola iberica; a.k.a. S. tragus; a.k.a. Prickly Russian Thistle) has become an emblem of the west, but it no more belongs on the prairie than cattle or sheep; cowboys or spurs. It is a nasty, practically leafless plant covered with thorny bracts. Its diffuse branching gives the plant a globose silhouette. When its seeds have ripened, it breaks off at the base and harnesses the wind to roll and bounce its way across the landscape distributing its seed far and wide; or at least until it hits a fence. Here is a photo of it in flower. Note the spines behind each flower. They are very sharp and most unforgiving. Classically a western weed, it is actually found throughout North America, though less common in the east and south.
Amid the waycross weeds and cow patties, I was able to find some interesting native plants. In over-grazed country such as this, one could classify the native plants into three categories; those that hide from grazers, those that fight grazers and those that suffer local (if not global) extinction.
The hiders are either growing in association with some form of grazer deterrent such as a clump of spiny Tumbleweed. Or they seeking refuge in the most floristically rich remnants of the whole prairie region; road ditches. It is here that you find the shattered remains of a once functioning ecosystem shamefully cast with road kill, Wal-Mart bags and cool season Eurasian grasses.
Here is Lygodesmia juncea (Skeletonweed) hiding in a prickly pear.
Other plants found hidden in the thorns include two species of Machaeranthera. The blue flowered Machaeranthera canescens was probably the most common native bloomer I found during my visit. Just about anywhere sheep couldn't get their chompers, this plant was growing.
Machaeranthera canescens was pretty easy to key out and was in most of the wildflower guides I had with me. However, M. pinnatifida (below) with its yellow florets posed a real challenge. I don't know many eastern genera that have yellow AND blue flowered species, so though the keys would take me to Machaeranthera, I wouldn't accept it. Finally, I ran it through the key to species and found the error of my ways. It still doesn't sit right, but I'm sure far greater minds than mine have agreed to it.
Machaeranthera pinnatifida was one of the few plant specimens collected by Meriwether Lewis on the Voyage of Discovery. As with most of the Lewis collection from said journey, it was described by Fredrick Pursh. So the story goes, he was only supposed to look at the specimens while visiting the States. Instead, he smuggled a stack of them back to England where he described them. In a twist of irony, most of the unabducted specimens were severely damaged or lost. Thus through Pursh piracy do we have any undamaged plant collections from the famous excursion.
Here are some road ditch refugees I encountered. This is Senecio riddellii. This was the only specimen I saw and it was closer to the mountains in a transitional area.
Unfortunately, even road ditches are rarely safe for plants that have escaped grazing. Humans have no tolerance for "unmowed" areas. So, in the name of duty to an ill perceived aesthetic, road ditches across America are regularly mowed. Here is a photo of Heterotheca canescens that I would say is standing defiant, if its defiance did not come in the form of lying procumbent. Normally an upright plant, it has become prostrate in the face of the mowing.
My third category consists of plants with weapons. These fighters defy cattle and sheep with raised swords (thorns/spines/prickles) or toxic potions (alkaloids and other sap-based chemical concoctions of a toxic nature). Gutierrezia sarothrae is of the latter persuasion. It is one of several poisonous native species that increase with grazing. Toxins within the plant tissues cause abortions in cattle and sheep (no Roe v. Wade here).