Wednesday, August 9, 2023

Here come the Four Horsemen of the Prairies

Panicum virgatum in Open Space area, in Broomfield, CO

Colorado is short grass territory (or at the least the eastern part of the state is), but as summer here is getting into full swing, I noticed that some of the iconic tallgrass prairie species are starting to show themselves.

The Four Horsemen of the Prairies refers to four species that tend to dominate the prairies farther east. The ensemble cast includes Andropogon gerardii (Big Bluestem), Panicum virgatum (Switchgrass) , Schizachyrium scoparium (Little Bluestem), and Sorghastrum nutans (Indiangrass).

Sorghastrum nutans in Broomfield, CO

I must admit that I was not really looking for them, engrossed as I was by the more western oriented species here, but I was walking along one of the Open Spaces in Broomfield when I spotted what looked to be Panicum virgatum in flower. The largish specimens lined part of the path, and a quick check of the flowerhead confirmed the identity.

I've always been a fan of this species as an ornamental, but seeing it in situ always is a treat, especially when in flower.

Sorghastrum nutans in Broomfield, CO

The second "horseman" I saw was one that for one reason or the other, I have not encountered much. This time, I found a slew of Sorghastrum nutans (Indiangrass) flowering along a sidewalk in Broomfield, CO, as well as in the various trails around Boulder.

Many people consider it a beauty, but personally, the fleshy colored and awned flowerheads of the species has never struck me as particularly attractive. Nevertheless, I was enchanted by the small flowerheads, which had escaped the mower blades by virtue of being shielded underneath some metal handhold along the path.

Schizachyrium scoparium along sidewalk in Broomfield, CO

And then there's Schizachyrium scoparium (Little bluestem), which I have owned as an ornamental and is an attractive plant to me. Unfortunately, the single specimen I have stumbled upon so far was still in the earlier stages of flowering, but I am looking forward to seeing more of this species going forward. 

Ladybug on Bothriochloa ischaemum(?). Where art thou Andropogon gerardii?

I was also on the lookout for the biggest horseman of all - Andropogon gerardii (Big Bluestem), but all the lookalikes I found at first seemed to be of some other species...specifically, Bothriochloa ischaemum, which is called yellow bluestem or King ranch Bluestem (in Texas).

Andropogon gerardii near Enchanted Mesa Trail, Boulder, CO

There are trails in that city called Lower and Upper Bluestem trails, and so I expected to find bluestems in the area, which I did. Unfortunately, most seemed to be yellow bluestem (Bothriochloa ischaemum) at this time.

It did not help that my identification skills aren't the best, but I finally found specimens of this large species during one of my hikes in Boulder. Not, as it turns out in the bluestem trails, but in trails closer to Chautauqua Park. Perhaps later in the season this tallest of the Four Horsemen will make its presence more widely known.

Sporobolus michauxianus (formerly Spartina pectinata) near Lower Bluestem Trail, Boulder, CO

Finally, I also found a really tall and attractive species that I identified as Sporobolus michauxianus (formerly Spartina pectinata). This is commonly called Prairie Cordgrass here, and it has amazing
pinkish anthers! When I first saw it from a distance I thought it was some weird A. gerardii, but I'm happy to have met the acquaintance of another spectacular looking member of the Poaceae during my trip to Colorado.

Sporobolus michauxianus (formerly Spartina pectinata) near Lower Bluestem Trail, Boulder, CO


  1. For 45 years I've worked hard to be open-minded about nomenclatural changes, and I deal with them a lot. But moving Spartina into Sporobolus was too much. Others feel the same, including ITIS, FNA, and the Rocky Mt Herbarium where I work (flora of WY checklist). The many authors of the following paper (2019) make a strong argument for retaining Spartina:

    1. Yeah, I've seen the paper. The funny thing is this controversy actually leaped into non-botanical realms because of the popularity and use of the name "Spartina" in daily usage. I can't seem to find an interesting lay article about this that I read once but will post it when I do find. I'll be's much easier to remember Spartina than Sporobolus.