Monday, September 6, 2021

How roads are aiding our worst plant enemies

Japanese stiltgrass growing on abandoned railroad tracks along Ashokan Rail Trail
I was hiking the Ashokan Rail Trail in New York and noticed how the gravel path was frequently lined with masses of the invasive grass Microstegium vimineum (Japanese Stiltgrass), which crowded out other invasives, as well as the native flora.

This predilection of the species for roadsides and paths is one that I am familiar with, and so once I got home I looked up whether there was any reason for its behavior. My first thought was that roadsides created an environment with higher light levels than the interior of the canopy, but it turns out there are other reasons why such man made strictures aid invasive plants in general

The characteristic silver midrib of Japanese stiltgrass
Large scale studies have shown that M. vimineum presence in forests was strongly correlated with the presence and proximity of roads and other man-made paths. The probability of finding this species along the east facing sides of roads was as high as 83% in one study area. In addition, experiments revealed that the natural spread of this species was greatest in patches closer to roads, and that these patches also tended to have higher populations.  There was something in the areas around roads and paths that proved advantageous to the proliferation and spread of this invasive species,

Japanese stiltgrass lining the sides of a hiking path
One interesting and important finding from studies of M. vimineum is that the species if left to itself spreads very slowly, with seeds landing only 1 to 2 meters away from the parent plant. This was perplexing because land managers noticed that Japanese stiltgrass can quickly spread throughout an entire forest within a few years, which implied a rate of invasion that was orders of magnitude faster than it should be.
Japanese stiltgrass expanding from roadside into forest interior

It turns out that human activity along the forest roads is one of the major causes of the rapid and unnatural spread of stiltgrass in invaded forests, whether it's from hikers picking up seeds as they trudge along hiking paths, or vehicles doing the same along passable roadways.

In addition, the forest roads themselves can create conditions that are environmentally advantageous for this invasive grass. For example, the use of limestone gravel in many unpaved roads can raise the pH of the surrounding soil, which is favored by M. vimineum.

Unfortunately, it is neither possible nor perhaps even desirable to completely remove all human structures from parks and other forested areas in a quest to return the forests to their original pristine condition, But we can at least minimize the negative impact we have on these environments through more studies that delineate the many ways our presence in the natural world affect the denizens of the forests.

Sunday, September 5, 2021

Andropogon gerardii as an ornamental

Andropogon gerardii "Blackhawk"

 I've been interested in using various ornamental grasses in my yard, and last year I finally decided to test some of the Andropogon gerardii cultivars in the market.

I was not convinced this species had what I wanted in an ornamental grass, but I wanted to at least make sure I wasn't missing something.

Andropogon gerardii "Blackhawk"

I bought an A. gerardii "Blackhawk" and an A. geradii "Raindance". The former surprised me this Spring by prematurely coming out early, but then seemed to have problems and its above ground structures wilted. It was reduced for awhile to a few small stems that sprouted from the periphery, and I fully expected the plant to die completely or to only come back next Spring.

However, several months later the ornamental grass had come fully back, and had even pushed out tall inflorescence that towered above the shorter leaves.

Andropogon gerardii "Blackhawk"

I took some time to take some macro shots of the flowerheads of the 2 cultivars, but I must admit I am not a big enthusiast of the species as an ornamental. The flowerheads came up at different heights, and I just could not shake the feeling that the "Raindance" especially looked like it was simply a grassy weed that had not been pulled out.

However, the cultivar "Blackhawk" has at least one redeeming feature, and that is its dark color. The leaves right now are a very darkish red, and they are supposed to turn almost black in late September. This unusual color of the cultivar perhaps makes up for the somewhat disappointing flowerheads.

Overall, I think the Andropogon cultivars do not match the beauty of other native ornamentals, such a Panicum virgatum or Schyzachyrium scoparium.

Sunday, June 6, 2021

Frankenstein's Plants: Natural Genetic Engineering in Grasses


Frankenstein foreground from Wikipedia (Universal Studios, NBCUniversal). Background is Phragmites australis

The grasses (Family Poaceae) are the most successful and economically important plant family today. They are supremely adaptable and hardy, and exist in numberless hordes from the rainforests of the equator, to the driest deserts of the American West, and even to the cold and almost lifeless vastness of Antarctica. 

The ability of species in this family to adapt to different environmental conditions has been one of the factors which has made it so successful, and researchers have recently elucidated one of the reasons for this adaptability.

A new study has discovered that many grasses can readily absorb novel genetic information from  their environment, and incorporate them into their own genome (Hibdige et al, 2021)! They do this via a process called Lateral Gene Transfer (LGT), where a species can acquire new adaptive genes and traits from completely different species without any sexual reproduction.

Echinochloa crus-galli had evidence of at least 10 LGT

The groundbreaking study showed that many grass species have been involved in lateral gene transfer of multiple genes, some of the genes coming from other grass species that are far removed in terms of  evolutionary relationship.

The researchers looked at 17 species for protein coding LGT, examining from 15,000+ to  well over 30,000 genes for each species tested. They found that most of the genes had an evolutionary history similar to the species that harbored them, indicating that they had been passed down through the generations from parent to offspring as expected. But more than a hundred genes were found where the evolutionary history of the gene did not match the species.

Zea mays (maize/corn) had at least 11 LGT

This evidence of LGT was found in 13 of the 17 species tested, with Alloteropsis semialata showing 20 instance of LGT! The species that showed evidence of LGT included not only wild species, but several domesticated ones as well, including maize, millet, and wheat. In this case, maize (Zea mays) had 11 LGTs received from Chloridoideae and Paniceae, while wheat (Triticum aestivum) had 10 LGTs received from Andropogoneae, Chloridoideae and Paniceae. The researchers noted that the LGTs may be beneficial for the crops, as the transferred genes included functions related to abiotic stress tolerance and disease resistance. 

Such instances of LGT are an amazing way for a grass to "leap frog" the slower evolutionary pathways and suddenly acquire traits very quickly, some of which are not only useful but staggering in their significance. For example, in another earlier study (Christin et al, 2012), researchers looked at the grass genus Alloteropsis, which contain species that  use C3 or C4 photosynthesis. They discovered  that fundamental elements of the C4 pathway (which is very adaptive in hotter and drier environments) were acquired via LGT from C4 grass taxa that diverged from the Alloteropsis group more than 20 million years ago!  

Distribution of LGT in tested grass species

The mechanism of this lateral transfer of genes is still unresolved, although the researchers noted that it seems to be more prevalent in species that have rhizomes. Such grasses have the capability of producing full individuals from broken pieces of their rhizomes, so one could imagine a situation where an LGT between these below ground structures and a concomitant separation of the rhizome later could lead to new separate individuals with sexual apparatus containing the gene. 

I am reminded again of the rhizomes of cogon grass (Imperata cylindrica), which have very pointed tips and have been shown to puncture other species of grass as the cogon expands. Perhaps such instances of hostility was a gateway to the prevalence of LGT in grasses, or perhaps it is only one of many multiple mechanisms for such an absolutely amazing phenomenon.

The sharp pointed rhizome of Imperata cylindrica

Literature Cited

Christin PA, Edwards EJ, Besnard G, Boxall SF, Gregory R, Kellogg EA, Hartwell J, Osborne CP. Adaptive evolution of C(4) photosynthesis through recurrent lateral gene transfer. Curr Biol. 2012 Mar 6;22(5):445-9. doi: 10.1016/j.cub.2012.01.054. Epub 2012 Feb 16. PMID: 22342748.

Hibdige, S.G.S., Raimondeau, P., Christin, P.-A. and Dnning, L.T. (2021), Widespread lateral gene transfer among grasses. New Phytol.

Sunday, May 30, 2021

Fat leaves and thin leaves: How they can tell us where grasses evolved

Correlation between leaf shape and habitat type across 578 grass species (Gallaher et al, 2019)

I hike a lot, and many of the places I hike into are in forests and woodlands, so it's no surprise that I've become somewhat familiar with the grasses that inhabit the shaded interior of these forested environments. 

One thing I have noticed is that the denizens of these habitats tend to have wider leaves compared to species that live out in the open, and I just read a paper that used this fascinating fact to try to resolve the evolutionary origins of the family Poaceae.

The wide leaves of Oplismenus undulatfolius, which inhabit the shady undergrowth

The evolutionary origins of grasses are still under intense study, but differing hypothesis place their original habitat either in forest interiors, in the open, or in forest margins. A new study sought to delineate these options by looking at the various leaf shapes in grass species (Gallaher et al, 2019). Forest grasses it turns out, do tend to have wider leaves than those species in the open, but unfortunately such changes in leaf shape might also be affected by other factors, such as climate and the photosynthetic pathway used by each species (whether C3 or C4).

The broad leaves of Dichanthelium clandestinum, another denizen of more shaded areas

In order to determine how various factors influenced leaf shape and size, the study generated phylogenies for 578 grass species representing all the Poaceae tribes and subtribes, and approximately 75% of all grass genera. Leaf shape for the various species in this phylogeny was then correlated with precipitation, solar irradiance, temperature, photosynthetic pathway, and habitat.

They found that leaf shape in the grass family was strongly correlated with the habitat of the species, and that leaf shapes across the entire family converged towards certain shapes becoming associated with specific habitats. So for example, open habitats tended to have grasses with linear leaves, and ovate leaves tended to be present in grass species in the forest understory. Meanwhile, species that lived in forest margins tended to have lanceolate leaf shapes, an intermediate form between the shadier forest interior and the more open plains. They also found out that leaf shape is not strongly related to all other variables, whether it be temperature, precipitation, solar radiation levels, or even photosynthetic pathway. In addition, they noted that grasses have smaller leaves in open and drier areas, and in areas with high solar irradiance.

Ammophila breviligulata with narrow leaves. Habitat is open beach areas.

Interestingly as well, they noticed that the evolution of leaf shape closely tracked habitat changes over the course of grass evolution, and their estimates placed the forest understory as the most likely ancestral habitat of the grasses. Looking within the family, they found that the most probable habitat of the bistigmatic clade, core grasses, BOP clade, Oryzoideae, and Bambusoideae was forest margins, while the crown node of the Pooideae was either derived from open areas or the forest margins,

In addition, they estimated that there were between 12 to 41 transitions by grasses in the move to open habitats over evolutionary time, and all of them were from forest margins. This highlighted the importance of the forest margin ecotone as a launchpad to the eventual diversification and movement of many in the family to having more linear leaves as an adaptation to open environments. Linear leaves are advantageous in these less restrictive habitats because they allow faster heat loss to avoid damage to leaf tissue, as well as help prevent mechanical damage due to wind and other stresses. 

All these changes in leaf shape as grasses moved from the forest margins to open habitats occurred in the Cretaceous or Paleocene, which was long before the first signs of grass-dominated ecosystems in the Eocene, and the eventual dominance of grasslands beginning in the Miocene. 

So the next time you are hiking, take note of the grasses and how their leaf shapes tracks the environment, and marvel at the evolutionary changes that allowed this family to escape the shadier environments of the forest to eventually claim dominance of the wider open spaces.

The narrow leaves of Panicum virgatum, another typical denizen of open areas

Literature Cited:

Gallaher, T.J., Adams, D.C., Attigala, L., Burke, S.V., Craine, J.M., Duvall, M.R., Klahs, P.C., Sherratt, E., Wysocki, W.P. and Clark, L.G. (2019), Leaf shape and size track habitat transitions across forest–grassland boundaries in the grass family (Poaceae). Evolution, 73: 927-946.

Tuesday, May 18, 2021

Ya picked the wrong plant to mess with pardner!

Phalaris arundinacea in 2020, with Yellow Flag Iris behind and to the right
Iris pseudacorus (Yellow Flag Iris) is a non-native that is found in semi-aquatic and aquatic habitats throughout North America. It is an attractive plant with yellow flowers that nonetheless can use its rhizomes to form dense monotypic stands that displace other plants in the area.

I was interested in the fact that the species co-existed with Phalaris arundinacea (Reed Canary Grass) along the shores of a nearby pond, and I have been watching the two species grow quickly this Spring.

Yellow Flag Iris surrounded by yellow border, and P. arundinacea to the left
There are large groups of Yellow Flag Iris around the pond, but the one I was interested in sat right next to and behind a big stand of Reed Canary Grass, their respective ramets almost intermingling with one another.

The Iris seemed to have sprouted tall earlier than the grass, but the latter quickly made up the difference and at this time is more than double the height of its erstwhile competitor.

Yellow Flag Iris (foreground), P. arundinacea (back), cattails (tall plants to right)
Both species are weedy invasives, and both have been known to aggressively outcompete and take over wetlands and other semi aquatic and aquatic environments. So I am very much interested in how the meeting between these two plants will resolve itself over time.

One thing I already noticed is that the Yellow Flag Iris clump next to the grass seems to be smaller than the one farther away, and have yet to bloom while their brethren have already pushed out their yellow flowers. But perhaps this is simply because that group is younger, and not because of competition from the Reed Canary Grass.

On first glance, the much larger P. arundinacea seems to be the clear favorite. I can almost see it looking at the Iris and saying "Hmmmmm...ya picked the wrong plant to mess with this time pardner!" 

But there are reports that show allelopathic activity in Yellow Flag Iris, and it is fairly common in the plant world for seemingly innocuous smaller plants to be the more aggressive and successful competitor, so I will definitely be looking with interest on this spot over the summer.

Saturday, May 8, 2021

A rare flowering of Japanese Blood Grass - that isn't so rare after all...

Last year I posted about the flowering of my ornamental Japanese Blood Grass (Imperata cylindrica), and noted that such flowerings were supposedly very rare. 

Interestingly enough, I was surprised to find that the same cluster of JBG had again flowered this year (and at about the same date!), with 2 flowerheads coming out of some of the more peripherally positioned ramets.

The flowerheads were already a bit spent, and the drizzle that caused them to droop under the water load did not help when I first saw them, but there was no question that flowering of JBG may not be so rare after all. Although perhaps some unique environmental condition in that cluster's location is causing this annual flowering, it's certainly unusual for this to happen (according at least to reports on the web).

Monday, April 12, 2021

Sentinels of the Dunes

I posted awhile back about the importance of grasses in maintaining the dune ecosystems that are the foundation of coastal areas. Without such grasses, we would not have the wide sandy beaches that give people so much joy. In the northeast USA, the predominant species is Ammophila breviligulata, which I also discussed in an earlier post. During our trip to Florida I had ample opportunity to see another species that becomes dominant as one goes farther south.

Dried seedheads in Tybee Beach
Uniola paniculata is a larger species that can grow to 2 meters high, and it is easily identified by its seedheads. I encountered it first in Tybee Beach, near Savannah, GA. It was March, so the inflorescences were all dried and brown, but no one can mistake the beautiful seedheads for anything else.

Like other dune grasses, this species accumulates sand around it, and in fact grows much more rapidly when buried in it. It reproduces mainly by asexual means, by forming buds along the bases, but it also produces seeds. The seeds reportedly can be carried long distances by ocean currents! 
A provider of nesting for various birds at Tybee Beach
As I walked along Tybee beach, I looked in wonder at the tall dunes that dominated the rear of the beach, each topped by stands of U. paniculata. They looked almost elven amidst the whitish desolate sands, and I gave thanks to these Sentinels of the Dunes, who stand watch to protect the integrity of the beach, and thus gift us such blessings.

Sunday, April 4, 2021

Rapid expansion of an invasive grass as viewed using Google StreetView

Cogon grass flowering
Last month I talked about using Google Street View as a tool to view the progress of invasive species over time. The example I used showed how a row of Neyraudia reynaudiana (Burma Reed) appears and fills the side of a road over the course of several years, but one cannot tell from the images whether it was outcompeting other plants or simply filling an empty niche.

In contrast, the series of images that I viewed in Google Street View recently clearly shows another invasive grass actively displacing other species as it expands. The location in this case is along a roadside in Kissimmee, Florida, and the invasive species is Imperata cylindrica (Cogon grass).

Cogon grass in 2011
Cogon grass is much smaller than Burma Reed, but it shows a characteristic form when seen even from a distance. It forms dense clusters of relatively straight blades, and the earliest image from 2011 has this invasive grass occupying only around 25% of the distance between two electrical poles.

Cogon grass in 2014 (in red)
However, images from 2014 show that the dense cluster of I. cylindrica had expanded to cover perhaps 50% of the distance, and by 2015 the invasive grass had seemingly already bridged the gap. By 2016, there is no doubt that the Cogon grass had managed to reach the opposite electrical pole and had displaced other plants.

Cogon grass in 2015 (in red)
I visited the area recently, and I measured the distance between the two poles as approximately 50 meters. This means that the Cogon grass cluster expanded laterally at around 7.5 meters per year.

Cogon grass in 2016 (in red)
Interestingly enough, this cluster continues to expand along the roadside even today. In 2018, the vegetation that lies to the left of the images above does not seem to show any Cogon grass infestation (see below).
No clearly visible cogon grass in 2018 between these 2 poles

But when I visited the location in March 2021, the cogon grass had occupied the area all the way to an optical cable line marker, which was placed about halfway between the poles. 

Cogon grass reaches halfway point by 2021
It would be interesting to continue to monitor the expansion of this invasive cluster later, when I again drop by the location in late 2021.

Saturday, April 3, 2021

Flowering of Imperata cylindrica (Cogon grass)

I love seeing a grass flowering en masse, and this goes double for a species with a beautiful inflorescence.

Although Imperata cylindrica (Cogon grass) is an invasive, it has quite attractive flowerheads, which are white spikes that look fluffy as they mature (see image below).

A single flowerhead
A closer look at the seeds show silky hairs rising from the spikelet. The hairs aid in dispersing the seed by wind (see image below). 

Seeds of Cogon grass
When I visited Florida in March 2021, I managed to see some examples of mass flowering for this species. It is actively controlled as an invasive weed, but the fluffy flowerheads are so distinctive that I have repeatedly spotted even small clusters of this species along the roadside as I sped by in a car!

I'd like to share with you some photographs of the mass flowerings that I saw. Enjoy!

Monday, March 29, 2021

Neglecting the natural

This is going to be a short rant, so if you hate rants, please feel free to skip the post.

I am staying in Kissimmee near Orlando in Florida. As some people may know, this city hosts the theme park Walt Disney World. What most may not know is that there is a nearby preserve that is called the Disney Wilderness Preserve, which is maintained by the non-profit Nature Conservancy.   

I visited this preserve and I was amazed at the beauty of the place.

The major part of the preserve is open Pine lands with absolutely gorgeous fields of grasses (dominated by the usual Andropogon and Aristida spp), and sprinkled with multitudes of shrubs and forbs and other plants. Even though it was a scorcher of a day, I barely noticed as I was busy glancing around and taking pictures of the colorful landscape.

The sad part was that there was barely any visitors to the park. A handful of cars dotted the parking lot, and  we did not meet any other hikers in the trails themselves, although a couple followed in our wake for a short while.

Meanwhile, I am sure the nearby theme park was packed with people (or at least semi packed, given the still potent sting of Covid-19), who probably would not give a darn that this preserve exists. We live in a world where artificial pleasures reign supreme; a time when virtual excitement through videogames and other activities far removed from the natural are the norm.

I am not really mad about this. People are free to choose what fulfills their lives. But I am sad that such beautiful places as the Disney Wilderness Preserve barely attract notice in our modern frenetic world.

Sunday, March 28, 2021

A meeting of giants

Flowerhead of C, purpureus
I admit I am not your typical tourist. Sometimes I like to wander the streets of cities I visit, just looking at all the flora and fauna to be seen. This was the case when I visited Florida City in Florida, which is close to Everglades National Park and Key Largo.

I was walking along the sidewalk of a busy street in this smallish city (ok, it was Route 1, a state highway!), when I had to do a double take. Along a dead-end side street next to one of the many motels in that area was a long row of gigantic grasses! 

Long row of gigantic grasses
They were tightly packed and stretched in an unending row from the start of the street (SE 1st Ave) to its end near the motel back. The grasses rose to 4 meters in height or more, and above some were whitish flowerheads.

Schoolbus parked next to C. purpureus for scale. 
My first thought was that I stumbled on Arundo donax, but a quick inspection of the flowerhead nailed the species as Cenchrus purpureus (syn. Pennissetum purpureum), which has various common names such as Napier grass, elephant grass, and Uganda grass.

Young C. purpureus spreading across a recently fallow lot
The grass had spread from the row to infest a field of trees behind it. The land looked abandoned, but a quick look at Google Street View from previous years showed that it had once been carefully tended, with palms planted in neat rows. Now young Napier grass sprouted from all over the field, and I was thinking that without tending that the lot would soon be filled with it. I also encountered another large stand of Napier grass east of the motels, along with smaller clusters that must have been derived from the larger stands (see image below).

C. purpureus in yellow, N. reynaudiana in red.
Interestingly enough, I spotted other large grass stands in the distance in the empty lot, but a quick look showed that they were a different species!

I trudged into the lot and found out that the new grasses were Neyraudia reynaudiana (Burmareed), their gigantic forms topped by huge plumes of brownish flowerheads. They were scattered in small clusters, and the nearest group was about 30 meters away from the equally tall Napier grass.

Neyraudia reynaudiana
I wondered what would happen when the two species finally met in that empty lot. Would one species be dominant over the other, or would they coexist, the two groups forming a field of gigantic grasses with distinctly different flowerheads? Which grass would prevail in this clash of giants?

Another interesting thing is that I have seen both species all over Southern Florida, but they both become much rarer as one travels north. I have not seen Burmareed in Lake Okeechobee (though I have seen what I took to be Phragmites australis in the distance next to the lake), while Napier grass was quite abundant on the northern lake shore. However, once one gets closer to Orlando, the glimpses of giant grasses becomes rare to non-existent, and I have only seen one cluster of Napier grass in the Orlando area. The specimens were located in Shingle Creek Regional Park, and they seemed a bit unhealthy looking.

N. reynaudiana on the road to Everglades National Park
It is a change to the landscape that is quite evident, perhaps even to the eyes of laymen. The land of giant grasses transforms into a land filled with Andropogon sp. and Aristida sp., much smaller grass species that nevertheless dominate many areas in a way that even the giants might envy.

Spider lurking in a C. purpureus inflorescence