Elymus is a wonderful genus of grass to study. Most of its members exhibit beautifully complex breeding systems that challenge, stretch and contort what would otherwise be our oversimplified and redundant definitions of species. Those interested in how and why such breeding systems emerge again and again from the natural interface of organisms and the environment are encouraged to read "Plant Speciation" by Verne Grant. It's an older reference, but it is still relevant and is far from outdated.
You know how in the movie, based on the Stephen King book, "Christine" the nerd slash soon-to-be vigilante hears the car he loves telling him that it can repair itself after the jocks trashed it and pooped on the dashboard? How he says "okay.... show me." and then the headlights come on with eerily piercing music? I feel like that when I find an Elymus in the field. My heart races faster and I breathe deeper, like something out of the ordinary is going to happen and we won't be the same afterward; like the top of a roller coaster. But I bend to the dramatic when it comes to grasses.
Here's an example of how exciting these grasses can be. In the photo below are four spikes of Elymus. All were growing within a few meters of each other. The one on the left fits the morphology of Elymus virginicus, sensu stricto, and it would key quite readily to that species. The one on the right fits and keys well to E. hystrix. The two in the middle are stones of the bridge between them. I say "bridge" instead of "path" because the two species on the ends are very much divided; there is a hot chasm of evolutionary pressure between them. But there is also an occasional bridge over said chasm.
Here is a close-up of the Elymus virginicus spike. Notice that the spike is/was partially included in the sheath of the upper leaf, the appressed spikelets and the broad glumes (they're the the things that look like upside down kayaks). Now scroll down to the fourth image in this series.
This is E. hystrix. It is dramatically unique when compared to E. virginicus. The spike was well exerted above the upper most leaf of the stem. Notice the spreading spikelets and that the glumes are reduced to tiny whiskers at the base of each spikelet.
The typical habitats of E. virginicus and E. hystrix are also very different. The former prefers mesic floodplain forests and woodlands while E. hystrix prefers dry to dry-mesic upland forests and woodlands. The particular spot where these four plants were found was a four-wheel drive road along the slope of a dry upland forest. The surrounding woods up to the road had numerous E. hystrix plants. On the downhill side of the road an erosion hump had been constructed to divert water off the road. This created a mesic "flood" zone perched about 75 meters above the floodplain. One way or another, a population of E. virginicus found that spot and formed a large colony. Intermixed with the E. virginicus plants were several plants that looked like the second photo in the series above which I, and noted Kansas botanist Jacob Hadle, interpreted as possibly being a F1 hybrid. On the edge of the colony we found two plants that looked like the third photo which we interpreted as a backcross between the F1 hybrid and an E. hystrix parental.
Of course, we are guessing at the relationships here, but when scrolling through the four photos you can see there is certainly a continuum of relationship there. The biological/ecological question is why and how does this happen? That is a BIG and fascinating subject to which I refer back to Verne Grant's "Plant Speciation".
Here is another example. In the photo above, the plant on the right is E. hystrix, the plant second from the right is E. glabriflorus and the remaining three plants are presumed to be F1s. In this scenario there was abundant E. hystrix in woods that were recently opened with fire (really hot fire I might add). The opening of the understory to light had likely encouraged some E. glabriflorus to arise like a phoenix from the ashes whereupon it created a downstairs mix-up with the natives.
How about another? Here we have E. virginicus on the left, E. villosus on the right and a very confused F1 in the middle. Notice the prairie in the background. These plants were actually growing in what WAS a wooded draw. You can see remnants of the trees in the background.
"More, more!", you say? The first photo below is E. curvatus; a species recognized by having a long spike that is usually included in the upper leaf sheath and that has short awns on the lemmas. The second photo is an immature E. canadensis characterized by its long awns and curved inflorescence. The third photo is their devil spawn. Both occur in prairies. This scenario consists of a prairie restoration where E. curvatus, which tends to like disturbed areas but is not what I'd call "weedy", volunteered into a zone where E. canadensis was seeded. Perhaps you are noticing the theme of disturbance induced hybridization at this point.
I don' t have photos of the parentals, but the plant in the photo below formed an aberrant population along a rock bottomed ephemeral stream corridor. It was growing with E. virginicus and E. villosus.
Below is another oddball for which I have no explanation. It formed an extensive population that was dominating portions of the field in the background and also occurred in abundance along the forest edge. Most of the plants were strongly glaucous. It would key to E. virginicus var. intermedius, but it looks like there is some E. curvatus or E. riparius introgression going on here. Elymus hybrids usually don't form populations, so I'm really puzzled by this thing.
In case I've frightened anyone away from the study of Elymus with my crazy hybrid kooky talk, I should mention that these are very rare occurrences. The vast majority of Elymus are easily identified, true to their morphologies, and faithful to their habitats. However, once you observe this phenomenon in its obvious form, you begin to notice the ghosts of introgression past in just about any population you encounter. For some taxonomists, such introgression has been the basis for lumping many taxa of Elymus into subspecific ranks or even into obscurity. This need not be.
I believe that these introgressing complications, these melding fringes of genetic uncertainty where we want straight and clean species lineages are glorious verification of evolution in action. They are living examples of the vital processes that comprise the change of organisms in response to ever-changing environments. The botanist that finds them frustrating instead of exciting, that would deny these fledgling species recognition out of ignorance or malaise rather than celebrate the shifting mudslide of their preconceived notions with the patience, fortitude and intellect of a true scientist should tender their resignation, turn in their handlens or at least admit that they are mentally incapable of fathoming the degree of imagination nature so readily achieves. But, like I said, I get dramatic when it comes to grasses.