Monday, September 18, 2023

Second update on the rapid expansion of an invasive grass in Florida

Hillside with cogon grass. From Lingsat

The previous 2 posts on this topic:

Update on the rapid expansion of an invasive grass (December 30, 2021)

Rapid expansion of an invasive grass as viewed using Google StreetView (April 4, 2021)

About 20 months after the last update (December 30, 2021), I again visited the same location and checked on the pace of expansion of the Imperata cylindrica cluster.

The cogon grass cluster had been expanding at a rate of 0.6 meters per month to one side, and during the last check, it had moved 6 meters to the west (left) of a green optic cable marker (see pic below).

When I visited yesterday, the cluster had expanded laterally another 6 meters before encountering a large low lying tree (see pic below).

Cogon has continued lateral expansion all the way to tree on west (left). September, 2023

The cogon ramets had crowded to the right of the crown of the low lying tree, but has not yet been able to bridge the shadow gap and cross to the other side.

However, I found isolated ramets huddling under the tree's shadow, with the one furthest west about 3 meters in from the crown edge. In addition, the cogon cluster is at the same time growing around the tree from behind. The result of these two activities means that sooner or later, the cogon will make its way to the unshadowed west side of the tree. at which point it should again commence its rapid lateral movement.

Cogon slogging under the tree's shadow towards the other side. September 2023.

The expansion rate of 0.6-0.7 meters per month that I had calculated in previous posts was based on an unshaded environment. It's been 20 months since I checked in Dec 2021, and in that time, the cluster has moved around 9 meters sideways, which comes out to 0.45 meters per month. This is noticeably slower than before, but obviously understandable given the shaded territory that it is trying to cross.

An interesting side topic is the ability of the species to traverse shaded environments. Although there are some indications that cogon grass is able to tolerate some shading, the presence of ramets deep into the shade of the tree might be explained by something more interesting.

As a rhizomatous species, cogon grass may have clonal integration. That is, researchers have found that clusters of interconnected ramets have attributes that cannot be found in non-clonal species. Not only does information flow between the members of the genet, but nutrients and water can be translocated throughout the entire network of ramets. This ability to actively and deliberately move information and other materials allows these clonal grasses to withstand stresses in heterogeneous environments that separated individual plants cannot. 

Thus in this case, the ramets under the crown of the tree might be sustained by photosynthates flowing to it from the unshaded and larger clones. 

More information on clonal integration is discussed here:


I've been rather lax in checking up on this fascinating invasion recently (has 20 months gone already!!), but in future I'll try to update it every 6 months or so. 

Thursday, September 14, 2023

Life in the Cracks Part Deux (Vertical Edition)

The very first article I posted was in July 2019, when I marveled over all the varied life that existed around us without being noticed.

In that post, I highlighted Digitaria spp weeds that had sprouted up from the cracks in the parking lot of an office complex.

Life In the Cracks

I was reminded of this again while walking around a park in Broomfield, CO last month, and I noticed a wayward individual grass that had somehow germinated from an extremely narrow vertical crack going up the side of a bridge.

The base of the culm comes straight out of the narrow crack.

There were no other vegetation at all in the long crack, and given that it hadn't rained in a bit, I had to wonder how the specimen was surviving at all. The other question that sprung to my mind was how it got there in the first place, and the most likely explanation was that a wind blown seed had fond its way into the crack, and had been lucky enough to take root before it could be dislodged.

It was a Setaria sp (Setaria viridis?), members of which seem to have a proficiency when it comes to such an epiphytic lifestyle. I have seen members of this genus proliferating along walls in New Jersey as well, although none of those were in the same precarious situation as this lone Broomfield individual.

Flowerhead of the specimen

To most people, such minor miracles as this are not even noticed, or acknowledged. At most their eyes might hover fleetingly over the lone survivor, then dismiss it as just another weed and continue on.

But when I first saw this, I was amazed. Life, it seems, will always find a way. It will grow and exist if there is any way at all to do so, no matter how unusual or surprising its method. Life is persistent; it is dogged and stubborn. It will turn up in the most unexpected of places, and surprise us.

I hope I never get tired of having such feelings of amazement at the wonder of life.

ps. as an aside, the ability of members of the Poaceae to survive in what seemingly are epiphytic conditions again highlights the question of why the family does not have more real epiphytes, like the members of the Orchid and Bromeliad families. There are only a grand total of perhaps 2 grasses that are considered truly epiphytic, out of a membership of around 12,000 species. Why have grasses, which are so dominant in many other places, failed to capitalize on this niche?

The answer to the question seems to be tied to the fact that the Poaceae are mainly wind pollinated, and that such a mechanism is not optimal in the wet, humid and closed environments that are favored by true epiphytes. For more on this topic, click below:

Calling all orchid-wannabees: Where are the epiphytic grasses???

Sunday, September 10, 2023

A Short History of Ornamental Grasses

World's Fair Pavilion in Forest Park, in St. Louis

Ornamental non-bamboo grasses have become such a ubiquitous feature of suburban and urban landscapes nowadays, that it might surprise some people that their widespread use is a relatively new phenomenon here in the USA.

This was brought home to me after I visited the World's Fair Pavilion in Forest Park, St. Louis last week.

The park itself is amazingly large, but what interested me most was a building that was surrounded by large stands of beautiful ornamental grasses. This World's Fair Pavilion was built in 1909 from proceeds of the World's Fair that was held in 1904. It's built on top of a hill and is surrounded by a large expanse of lawn and other plants.

Gigantic Panicum virgatum in Forest Park, St. Louis

The largest Panicum virgatum specimens I have ever seen in masses graced both sides of the area in front of the pavilion. There were also stands of Miscanthus sinensis, as well as the usual stately Calamagrostis. These ornamental grasses dominate the landscape today, but pictures of the same pavilion from the 1930s showed no signs of the stately and graceful grasses. Instead, shrubs and bushes and trees were the norm (see image below).

The pavilion in the 1930s. From the Missouri Historical Society. Note the lack of ornamental grasses.

The drastic change in the landscaping is significant. Although the use of bamboo for landscape decoration was popular even during ancient times, ornamental non-bamboo grasses did not enjoy the same popularity. However, during the 1930s, the renowned  German nurseryman, Karl Foerster pushed for their use in Germany and Europe. He collected grass seeds and plants from all over the world, and after cultivating them in his nurseries he introduced them to the market.

Calamagrostis to the left, Panicum virgatum to the right. In Forest Park, St. Louis

Among the many plants he introduced, perhaps his most famous creation is the outstanding ornamental grass Calamagrostis × acutiflora 'Karl Foerster', which he released to the market in 1950 as a natural hybrid of C. epigejos (native to Europe, Asia and Africa) and C. arundinacea (native to Eurasia, China and India).

Calamagrostis in background, Cenchrus setaceus in foreground, in Colorado

This rise in the use of ornamental grasses in Europe was not mirrored in the USA until much later, but various growers were instrumental in pushing for this new paradigm.

In the early 1960s, Kurt Bluemel began the introduction of ornamental grasses into America through his nursery in Maryland, called Kurt Bluemel Inc. Educated in Germany and Switzerland, Bluemel was passionate about grasses, and by the time he passed away decades later, he was well known as Der Gras K├Ânig, the Grass King. 

Kurt Bluemel. From Baltimore Sun.

He is said to have carried his first grass specimens in his luggage when he came to America, and his collaboration with Wolfgang Oehme, a German-born landscape architect based in Towson, was highly influential in creating a growing appreciation for ornamental grasses in the country. Some of his notable works include creating the savannas at Disney World's Animal Kingdom, and Busch Gardens. 

Panicum virgatum

By the 1980s, the momentum behind ornamental grasses had finally reached a crux, and an influx of growers finally pushed it into the mainstream. In 1986, John and Jill Hoffman established the Hoffman Nursery in North Carolina, which specialized in ornamental grasses. 

John Hoffman. From Hoffman Nursery.

John's interest in ornamental grasses was stoked during a visit to Germany, where he met the plant breeder Ernst Pagels. Pagels was an enthusiastic supporter of grass-filled gardens, and this along with the support of his mentor,  J.C. Raulston at North Carolina State University, fueled his passion. Today, Hoffman Nursery is one of the largest suppliers of ornamental and native grasses in the country.

Miscanthus sinensis

The trend towards landscaping with grasses then moved from the East Coast to the West Coast through the efforts of people like horticulturalist John Greenlee. In order to complete an oak savanna project in California in the 1980s, he travelled to Kurt Bluemel's Nursery in Maryland, where he was astounded by the hundreds of varieties of ornamental grasses that were on display. He ended up trucking a load of the grasses in a tractor trailer from Maryland to California, and after a stint in Brazil with the renowned landscape architect Roberto Burle Marx (who is also held in high esteem in the aroid community), he finally opened the first ornamental grass nursery in the West Coast.

John Greenlee. From Greenlee Meadow Collection.

Fast forward to today, when people routinely use ornamental grasses both in residential and commercial landscaping. And although many of the varieties used are the showy exotics (such as Miscanthus sinensis and Cenchrus setaceus), the use of native grasses as ornamentals (such as Trypsacum dactyloides in Florida, and Bouteloua gracilis in Colorado) is also widespread.

Bouteloua gracilis in Colorado

Meanwhile, new varieties and species continue to be introduced into the market. Not only do they contribute linear structure to a design, but their ease of maintenance, resistance to herbivores like deer, and their ability to impart movement to an otherwise static landscape, make ornamental grasses perfect components for any project.

Looking out from the pavilion in Forest Park, St. Louis. White flowerheads are Miscanthus sinensis cultivars

Thursday, August 31, 2023

Update on Cogon Grass Reversion in Colorado

The previous article to this is here:

Cogon in Colorado: An Alarming Case of Natural Reversion from the Ornamental Variety

We will be heading back to the east this weekend, but before we leave I spent some time surveying the community for any other reversions.

I found a total of 17 clusters of Imperata cylindrica, and 12 of them had putative reversions. This means that more than 70% of the plantings gave rise to wild type Cogon grass. I mapped all the clusters for use later.

Cogon grass fills a planting area. The "hole" in the middle of the mass is because of the presence of a large sculptured rock

I determined that there was a reversion event by checking whether there were flowerheads and/or the body form had changed to all-green, along with a concomitant increase in height and size. Out of the 12 reverted clusters, a couple had flowerheads, but still had the reddish leaves and smaller size, but most of the reversions were distinctly different in vegetative form than the ornamental.

A short-statured bush is being choked by the surrounding cogon

This reversion of an ornamental form to the dangerous wild type again highlights the problem of ornamentals that are still being sold (including in big box stores) to consumers, even though some of the species are illegal in certain states (and in the case of cogon grass, the species is considered a federal noxious weed).

Unfortunately, the ornamental variety with its red-tinged leaves are beautiful, and even the wild type can be attractive. This is because the blades are quite straight and seem to rise up directly from the ground, and when I showed my wife the imposing stands of reverted cogon grass, she mentioned that they looked nice.

But not only is cogon grass a menace to native species, but it is also prone to causing large fires, and is thus a potential danger to people and human habitation.

Samples have already been given to the state university, and once it has been positively identified, actions to clear the infestations should begin.

Thursday, August 24, 2023

Hybrid Prairie Lawns in Colorado

Turfgrass to the left, natural field to the right, in front of residential complex in Broomfield, CO. The field is actually closer to the complex, which is to the right.

One of the things that has most impressed me during my stay here in Colorado has been the way they have managed to integrate natural components into the suburban and even urban landscape.

The so-called Open Spaces is one aspect of this. but I also found smaller examples that were even more immediate and accessible to people.

Turfgrass to the left, natural field in front of residential complex to the right

In many places I've visited, including Broomfield and Boulder, landscapers have integrated traditional lawn and ornamentals with natural fields of grass and forbs around residential and commercial buildings. In the picture above for example, traditional turf grass that remain cropped close to the ground stands next to an open field. 

Turfgrass lawn backstopped by natural grass field, in front of residential building

These hybrid prairie lawns (HPL) are quite attractive, and the natural fields pull the eye away from the rather dull and relatively boring turfgrass. Unlike turfgrass lawn, the natural fields changes in appearance over the course of the season, with more green tints in the earlier parts of the year, before the golden light browns of summer and fall as the grasses senesce. Another big positive is the significant savings to the property owner, since the fields are not irrigated, and mowing of the fields is kept to a minimum.

As far as I can tell, the fields in HPLs are kept quite natural, with most of the grasses being the usual naturalized exotics such as Bromus inermis, mixed in with natives such as Panicum virgatum and Sorghastrum nutans.

Bromus inermis, which is normally a big part of fields here

I kept wondering whether the HPL concept would fly in some other states. This part of Colorado is lucky because the area is naturally high desert, where open savanna and pure grasslands are natural parts of the landscape.

In a place like New Jersey for example, which does not normally have lots of natural grasslands, any space left untended would soon become a big mess of brambles and forbs and weedy plants, which isn't as "attractive" as prairies. Energy and money would be needed to maintain a "cleaner" look, and this would probably discourage landscapers from exploring possibilities.

I did notice even here in Colorado that parts of some natural fields have a proliferation of weedy looking forbs in them, but on the whole, the system seems to maintain a nice equilibrium of small and medium tall grasses, with some forbs mixed in.

This plus the heavily maintained turfgrass next to it proves that such HPLs are a great alternative to the more boring landscapes with pure turfgrass. 

 Now, that's a "lawn" that I would love to have all year round.

Panicum virgatum, another species that forms part of the field

Thursday, August 17, 2023

Barley and Millet: Yes, Some Foods Do Grow like Weeds

Hordeum vulgare (Barley)

Barley is the 4th largest in terms of grain production, behind the other grass crops such as maize/corn, rice, and wheat. The species was domesticated around 10,000 years ago in the Eurasian region, and most barley is used for animal fodder, with the rest being used as food or for the making of fermented products such as beer. 

I was walking along one of the sidewalks here in Broomfield, CO, when I noticed quite a few attractive looking grasses along the sides of a building construction site. They weren't the usual Hordeum jubatum (commonly called foxtail barley here), which is pretty abundant in the area, and instead looked like some kinda short wheat (Triticum aestivum).

Spikelets of H. vulgare

Intrigued by the specimens, I started looking more into it. In terms of identification, I like trying to figure out the various wheat-like species only about a bit more than I like trying to make some sense of the different wheatgrass species. But after poring over identification guides and some apps, I finally decided that what I was looking at was the common barley.

Well-developed auricles of H. vulgare

Hordeum vulgare is an annual from the subfamily Pooideae, and the fact that this crop species also grows as a weed is a revelation to me. It's like coming upon a vast field of rice that grew naturally, without any help from the hand of people. Nevertheless, it turns out that this species, even though cultivated for millennia, does indeed have the capacity to still grow adventitiously along roadsides and other off-field areas.

The specimens seemed to be concentrated in that small block, as I have not really seen it elsewhere in the area, which is also intriguing. In fact, close to this cluster (the next block over) I found a second grass species that is also used as a food crop.

Panicum miliaceum (commonly called Proso Millet) is in the subfamily Panicoideae, and is just one of the many species that make up the group of food crops called "millet".

Panicum miliaceum (commonly called Proso Millet)

Proso millet was first domesticated around 8000 years ago in Northern China. There are some suggestions that this species, because of its ability to be harvested in as little as 45 days after planting, as well as its ability to produce crop in very little moisture, may have formed the bridge between hunter gatherer lifestyles and more sedentary agriculture. 

Panicum miliaceum

The domesticated crop has a tendency to revert to wild type, and the single specimen that I found was growing near a construction site, next to some landscape plantings on the sidewalk. It formed an arresting sight, with the heavy flowerheads drooping in thick bunches almost to the ground.

It is tempting to imagine how these food crops were first domesticated. Perhaps some hunter gatherers who had missed out on snagging a large prehistoric herbivore were dejectedly slouching back home, when they chanced upon fields of Panicum miliaceum, their tops overflowing with ripe grains. Or perhaps the discoverers of this new food crop were women who had been searching for edible berries and other vegetable goodies. Maybe people were getting tired of the vagaries of hunting and searching for food, and decided that planting food crops close to you might be a better idea. Or maybe a plant started as a weed infesting earlier crop plants, but was later seen to be another good food source and thus domesticated. This was what happened in the case of oats (Avena spp), which started as weeds in barley and wheat fields. The study of how agriculture started is endlessly fascinating, and one that I'll likely get into in a future post.

As an aside, the sight of food crops like these still growing wild reminds me that humanity's time here on earth is but a blip in the much larger time periods that some species inhabit. If ever our kind dies out, whether through disease or war or some unlikely event that we cannot fathom, it's likely that many of our "domesticated" plants will revert back to their wild ways, their brief tenure as indentured "servants" to the "raging apes" soon forgotten in the dim corridors of time.  

Tuesday, August 15, 2023

How Invasive Grasses Killed Hundreds of People in Hawaii During America's Deadliest Fire in a Century

Wildfire near Yosemite National Park, United States, in 2013. (Wikipedia, public domain)

Invasive grasses have long been known to create grass-fire cycles that allow these species to expand rapidly across the environment. In such a process, the grasses provide abundant tinder material for fires, whether started naturally via lightning or through artificial means. Generally, they are optimized for utilizing and promoting fires due to several factors:

(a) their creation of high fuel loads, which refers to how much fuel is present and available to burn. Grasses in general, and invasive grasses in particular can form very high density clusters.

(b) their low live to dead biomass. Annual invasive grasses in particular create vast fields of very dry dead matter after they flower and seed.  

(c) their high surface to volume ratios. Grasses generally have thin blades, which means they have a lot more surface area compared to their interior volume. Higher values are correlated to shorter fuel ignition times, and hence faster fire spread rates.

Add in the fact that grasses typically recover rapidly following fires, and the result is that fires kill off most of their potential competitors, and allow the grasses to expand their range and continue the cycle ad infinitum.

A prime example of such a cycle is one undergone by Taeniatherum caput-medusae (medusahead grass), which along with Bromus tectorum (cheatgrass) and others have devastated vast areas of sage habitats in the Great Basin.

Hawaii is no stranger to invasive grasses, most of which were deliberately introduced as potential forage or as ornamentals, but have since escaped into the wild and have outcompeted the natives in the islands. These include Megathyrsus maximus (called Guinea Grass in that area), Melinis minutiflora (called Molasses grass in some places), and Cenchrus setaceus (called fountain grass in some places).

Megathyrsus maximus spikelets (inset inflorescence), with purple stigmas and yellow-orange anthers

Last week, a massive fire destroyed the town of Lahaina in Maui and became the deadliest fire in the USA in a century. As of this writing, 99 people have been confirmed dead, but officials warn that the final tally could be double or triple that.

The initial cause of the fire is not known, but changes in the climate in Hawaii (including long-term declines in average annual rainfall and drought), coupled with the spread of invasive grasses to produce vast grasslands, are thought to be major factors in creating and maintaining the large wildfires after its initial start.

Escaped Cenchrus setaceus rows in Mulholland Dr, in Los Angeles, California

It's been a few years since I travelled to Hawaii, but I watched the popular TV series Lost a couple years back. This show was mostly shot in Hawaii, and it was interesting to see how many times I saw what seemed to be large expansive stands of Megathyrsus maximus, which is a large species and thus easier to see identify. The clusters were not only in savanna habitats, but also seemed to exist as smaller groups within forested areas.

I also remember visiting California this year, and seeing masses of escaped Cenchrus setaceaus along the roadsides in San Diego and even in Mulholland Drive in Los Angeles, where they doubtless increase the likelihood of spreading and exacerbating any incoming fire.

In the end, this major tragedy again highlights the importance of not only implementing measures to curb and address global climate change, but it should also focus people's attention on the importance of stopping the spread of invasive grasses. 

Perhaps most people may (sadly) not care about the destruction of sage brush habitats by such invasive grasses, but they surely will care about people's homes and lives being lost to the same types of invaders. A good start would be to enact legislation that will address this problem now, including banning or regulating the sale of invasive ornamentals and forage.




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


Tuesday, July 25, 2023

Cogon in Colorado: An Alarming Case of Natural Reversion from the Ornamental Variety

Click here for a new update to this article.

The highly aggressive Imperata cylindrica is normally considered an invasive weed, but it is sold as an ornamental in some places due to an attractive variety called Japanese Blood Grass or Red Baron.

This variety has reddish leaves and is significantly smaller than the wildtype form. It is also notably less competitive than the latter. In addition, flowering in this variety is extremely rare, and it is cold tolerant. 

Ornamental form in New Jersey

The problem with the ornamental variety is that it has been shown to revert to the aggressive green form under certain environmental conditions, and so this variety cannot be sold, traded, or grown in certain states that have major cogon grass problems. The fear is that it might hybridize with the green form to form very aggressive, and cold tolerant, varieties that can become problematic even in cooler areas.

Cogon grass stand in Broomfield, CO. The dense mass has started to insinuate itself into the nearby shrubbery.

Natural conversion from the ornamental to the green form is probably very rare, and in the many years that I have known it in New Jersey, I never encountered such an event. However, I was walking along a street in Broomfield, CO, when I had to do a double take and take a closer look at a stand of grasses. Rising from the dense mass were flowerheads that looked similar to the distinctive inflorescence of I. cylindrica

Spent flowerhead

Most had already lost their spikelets, but a few still had the characteristic fluffy white seeds of the species sticking to them.

White hairy seeds of I. cylindrica from the reverted stand

There was no trace of red blades in the stand, and the grasses were up to more than 1 meter tall, which is significantly taller than I've ever seen the ornamental variety grow. All indications pointed to the fact that these were wild type cogon grass. In fact, the stand looked exactly like any cogon grass stand in Florida, the dense mass almost excluding all other plants from living in it.

Spent flowerhead with a few fluffy seedheads still attached

I surveyed the area and found at least two stands of reverted cogon grass in the vicinity. In the second stand, there was a mixture of both ornamental and green forms, with the green forms sprouting multiple flowerheads as well. In both stands, a few other plants managed to hold onto their spots, including Bromus inermis, which is normally one of the dominant naturalized exotics here in the Boulder area. Most will probably succumb to the much denser and more aggressive I. cylindrica over time.

Dense mass of reverted Cogon grass fills up all the available space. The brown flowerheads to one side are from a few Bromus inermis that have survived in their midst

Broomfield, CO is definitely not a subtropical or tropical location, so to say that I was surprised to find green-form cogon grass in the place would be an understatement. The ornamental variety of cogon grass seems to be used here though, probably because the assumption is that the cold and snow would keep it in "safe mode".

The reverted wild type form is significantly taller than the ornamental form, and is green in color.

However, the record heat prevalent in the southwest right now is probably increasing the average temperature in this area as well. Add in the wet winter and spring this year, and conditions might be optimal enough for the ornamental variety to revert. 

Ornamental form between Calamagrostis spp.

The origin of the cogon grass is likely ornamental forms that had been planted along the sidewalk. I found a couple of these sandwiched in between the usual Calamagrostis ornamentals. 

The question on whether these naturally-reverted forms will continue to survive is important. Will the cold and winter of Colorado convert these back to the ornamental form going forward, or will the warming climate allow it to flourish and start aggressively taking over swathes of the environment?

Time will tell.

Note: I have contacted the relevant authorities who can handle these clusters, so they will probably be extirpated going forward.

Unlikely pairing of Bromus japonicus and Imperata cylindrica "Japanese Blood Grass"