More Evidence of Potential Animal Pollination In some Grasses

Purple stigma on the upper left of the hoverfly, as it looks around for yellow anthers

In previous posts, the topic of animal pollination of grasses was discussed.

Life without Animal Pollinators: Why Grasses Embraced the Wind

Bee mimicking fly on flowers of Phalaris arundinacea cultivar

I was looking at what I thought to be a small specimen of Andropogon sp. here near Boulder, Colorado, when I noticed that many small insects were landing on the flowerhead and spending time perusing through the yellow anthers.

The insects that buzzed and crawled among the yellow anthers and purple stigma seemed to all be hoverflies, similar to those that I had seen frequenting the flowerheads of Phalaris arundinaea in New Jersey. 

Hoverfly eyes a good meal

As I noted in the previous posts, the insects seem to eat the pollen directly using its extended proboscis, and this could facilitate pollination when pollen sticks to it and transfers to a stigma during its visit to another flower.

Like all grasses, A. gerardii relies on wind pollination for the dispersal of its pollen, and the reason behind its lack of dependence on animals is discussed elsewhere. But it would not make sense to turn down the services of insects and other animals when they could enhance delivery, and this is perhaps what is happening in this case.

Interestingly enough, there have been reports of other insects such as bees also rummaging among grass flowerheads, but I have yet to see such cases.

Winter is Coming: How Grasses Conquered the Long Freeze

Tundra (By Education Specialist)

There are vast areas of the world where cold temperatures create problems for plants.

Such "cold stress" happens when temperatures that are below what are optimal for plants creates physiological problems for the individual plants. Depending on the species, optimal growing conditions usually hovers between 10℃ and 30℃. 

There are two types of cold stress, depending on the temperatures involved.

Chilling refers to cold stress where the temperatures range between 0℃ and 15℃, whereas freezing refers to cold stress where the temperatures are below freezing (0℃). 

In the case of freezing, plants can respond via two different methods. Freezing avoidance is when the plant is able to delay or even prevent freezing altogether in their tissues. In contrast, in freezing tolerance, the plants do not prevent ice crystal formation, but they avoid damage by controlling the size of the crystals and/or where the crystals are formed. Freeze-tolerant plants can survive even freezing of their tissues, and represent the extreme adaptation to conquering the cold over long time periods.

Deschampsia antartica (c) Lomvi2 - Wikipedia

Grasses initially evolved as tropical plants that loved the warmth. But over time, the grasses have managed to adapt to the cold and have become the most widespread vascular plant family, and present in all continents. Indeed, the grass Deschampsia antartica is only one of two vascular plants that are native to Antarctica, and its optimal growing temperature is an amazing 10℃!

Freezing can kill grasses via the formation of ice crystals. At first, ice crystals form in the extracellular spaces between cells, which causes water to be pulled from the cell interior. The loss of intracellular water (and later solutes) results in dehydration and osmotic stress. As ice crystals continue to form into the interior of the cells, the cell membranes start to degrade and programmed cell death occurs.

The evolution of the ability to tolerate freezing in the Poaceae is fascinating, and is confined mostly to species in two different subfamilies of the Poaceae. Grasses in the subfamilies Pooideae (in the Northern Hemisphere) and Danthonioideae (in the Southern Hemisphere) live in cold temperate continental regions, and they have solved the problem in two different ways. 

Hordeum jubatum of the subfamily Pooideae (Northern Hemisphere)

The grasses in subfamily Pooideae in the Northern Hemisphere all use the C3 mode of photosynthesis, and are commonly called the cool season grasses. They include many turf grasses (such as Poa pratensis or Kentucky Bluegrass), as well as food staples such as Triticum aestivum (wheat), Avena sativa (oat), and Hordeum vulgare (barley). 

The ancestors of the Pooideae evolved about 67 million years ago in small niches during the formation of the Eurasian mountain ranges. In this group, ice binding proteins evolved which decreased the rate of the formation of ice, as well as altering the shape of the ice crystals being formed. These anti-freeze proteins prevent the formation of large crystals that can physically damage cells and tissues.

Cortaderia selloana from the subfamily Danthonioideae (Southern Hemisphere)

In contrast, cold-acclimated grasses from the subfamily Danthonioideae in the Southern Hemisphere have evolved a different method for conquering the cold. The members of this group are also C3 grasses, and include the large ornamental grass Cortaderia selloana (Pampas grass). The freeze tolerant members of this subfamily produce ice-nucleation proteins that allow them to control where ice crystals form. Thus, they can prevent damage by limiting crystal formation in the extra-cellular spaces and the leaf surfaces, but not within the cell interiors.

The independent evolution of such mechanisms by the Danthonioideae and Pooideae to tolerate freezing have enabled grasses to dominate large areas where there are extreme seasonal fluctuations in temperature, and contributed to the grassy world we live in today. 

As an interesting aside, at the other end of the temperature spectrum, C4 grasses such as those in the grass subfamilies Chloridoideae and Andropogoneae - which include corn/maize (Zea mays), the bluestems (Andropogon spp), sugarcane (Saccharum officinarum), and cogon grasses (Imperata cylindrica) - have extended the range of environments conquered by the Poaceae to much warmer and drier climes. 

For a quick look at the difference between C3, C4 and CAM photosynthesis in grasses, click here.

Muhlenbergia sericea of the subfamily Chloridoideae, a C4 grass

Finally, to read more about the fascinating topic of cold adaptation in grasses in depth, check out the references below.

Note: In addition to the specialized mechanisms of freezing tolerance above, grasses can deploy other additional mechanisms for coping with the cold that are beyond the scope of this shirt post, such as accumulating fructan in their vacuoles, using supercooling (for shorter cold spells), and increasing anti-oxidant enzymes.

Phalaris arundinacea of the subfamily Pooideae

References:

Timothy J. Gallaher, T. J. Gallaher, Paul M. Peterson, P. M. Peterson, Robert J. Soreng, R. J. Soreng, Fernando O. Zuloaga, F. O. Zuloaga, De-Zhu Li, D. Li, Lynn G. Clark, L. G. Clark, Christopher D. Tyrrell, C. D. Tyrrell, Cassiano A.D. Welker, C. A.D. Welker, Elizabeth A. Kellogg, E. A. Kellogg, & Jordan K. Teisher, J. K. Teisher. (2022). Grasses through space and time: An overview of the biogeographical and macroevolutionary history of Poaceae. Journal of systematics and evolution, 60, 522-569. doi: 10.1111/jse.12857

Schubert M, Humphreys AM, Lindberg CL, Preston JC, Fjellheim S. 2020. To coldly go where no grass has gone before: A multidisciplinary review of cold adaptation in Poaceae. In: Annual Plant Reviews online.Wiley.523–562.

The Tree and the Reed: How Wind Affects Grasses

Video above shows Phalaris arundinacea (Reed Canary Grass) being buffeted by wind.

There are many versions of Aesop Fable's The Tree and The Reed, a tale which first appeared in Ancient Greece, and whose moral about pride and humility still resonates to this day. One of the versions goes thus:

A Giant Oak stood near a brook in which grew some slender Reeds. When the wind blew, the great Oak stood proudly upright with its hundred arms uplifted to the sky. But the Reeds bowed low in the wind and sang a sad and mournful song.

“You have reason to complain,” said the Oak. “The slightest breeze that ruffles the surface of the water makes you bow your heads, while I, the mighty Oak, stand upright and firm before the howling tempest.”

“Do not worry about us,” replied the Reeds. “The winds do not harm us. We bow before them and so we do not break. You, in all your pride and strength, have so far resisted their blows. But the end is coming.”

As the Reeds spoke a great hurricane rushed out of the north. The Oak stood proudly and fought against the storm, while the yielding Reeds bowed low. The wind redoubled in fury, and all at once the great tree fell, torn up by the roots, and lay among the pitying Reeds.

The reeds mentioned in these tales were probably a hodge-podge of riverside-living graminoids. The original and most likely species that answers to this name is Phragmites australis (Common Reed), but the term may also refer to other grasses, such as Phalaris arundinacea (Reed Canary Grass), Arundo donax, Neyraudia reynaudiana (Burma Reed), various species of Calamagrostis, as well as a few other assorted members of the Poales. All these plants are herbaceous, with thin leaves that seem to support the central idea of the fable about wind resistance, but the reality is actually more complex. 

It is true that grasses are able to withstand gusts that would topple large trees, but they too can be negatively impacted by continuous strong winds, either due to shaking (seismorphogenic) or rubbing (thigmorphogenic) processes.

Some of the effects of wind include:

• Increased leaf transpiration, which means grasses lose moisture faster through their stomata. 
• Decreased leaf extension, which means the grasses produce less leaves.
• Slower growth rate.
• Damage to leaf surfaces, including displacement and smoothing of the epicuticular waxes, damage to the cuticle, collapse of epidermal cells and fracture of trichomes.

These effects increase with increasing wind speed, and older leaves are disproportionately affected.

In addition, studies of wind effects on wheat showed that there was significant reductions in grain yield when the grasses were exposed to strong continuous wind. There were less heads per sqm, less kernels per head, and each kernel weighed less than normal. All these negative effects show that Aesop's Fables was not exactly right when it marveled at the invincibility of reeds compared to the more arrogant trees during a storm. 

As an aside, I love seeing grasses swaying and dancing in the wind, especially when they occur in large masses. This is why I decorate my home with lots of ornamental grasses; their movement gives a very attractive active component to the home compared to static bushes and trees. But now that I know the effect of wind on these plants, I'm more careful about wishing for the stronger and damaging winds.

References

Pitcairn, C.E.R., C.E. Jeffree, and J. Grace. 1986. Influence of polishing and abrasion on diffusive conductance of leaf surface of Festuca arundinaceae Schreb. Plant, Cell and Environment 9:191-196.

Russell, G., and J. Grace. 1978. The effect of wind on grasses. V. Leaf extension, diffusive conductance, and photosynthesis in the wind tunnel. Journal of Experimental Botany 29:1249-1258.

Smika, D.E., and R.W. Shawcroft. 1980. Preliminary study using a wind tunnel to determine the effect of hot wind on a wheat crop. Field Crops Research 3:129-135.

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.

Bee mimicking fly on flowers of Phalaris arundinacea cultivar

I was taking macro photos of the flowers of my ornamental Phalaris arundinacea 'Strawberries and Cream" when I noticed several small (less than 5 mm) bee-like insects rummaging on the inflorescence.

The vast majority of grasses are wind-pollinated of course, but there have been cases of insect pollination, including by hoverflies.

The specimens visiting the grass flowers were identified as Toxomerus geminatus by Jeff Skevington in a Facebook group for hoverflies of the world.

In these hoverflies, the insect eats the pollen directly using its extended proboscis, and facilitates pollination when pollen sticks to it and transfer during its visit to another flower.

There were perhaps 3 or 4 total of the bee-mimicking hoverflies on the flowers at any one time, and  at first I was thinking they actually were small solitary bees, although a quick look at the photos shows the single pair of wings and stubby antennae that mark them as flies.

I have to admit it was interesting to see them at work, although taking good pictures was doubly difficult because of the high winds at the time.

A couple more pics below. Enjoy!

Bloom time for Phalaris arundinacea (Reed Canary Grass)

There is this small lake that has a paved path going around it, and we usually walk the path during our afternoon exercise.

When we visited the lake two days ago, I noticed a stand of tall (1.5 m or so) grasses that had started blooming. The grass had pushed aside other plants and formed a dense barrier along the side of the path.

I do not believe I had seen this stand in years past, and I noticed that scattered around the lake were other similar specimens, although much smaller and existing only singly or in somewhat small groupings.

I examined the plant and suddenly realized that these were wild Phalaris arundinacea!

This C3 invasive grass has somewhat loose panicles, and each spikelet has a single fertile floret and two much smaller sterile florets surrounding it. Under my macro lens the pink-purple anthers looked deflated, and here and there I could see white feathery stigma poking out. 

If you look closely at the macro shot above, in the spikelet in center you can see what looks to be 2 stigma and 3 clustered anthers poking out.

The ligule is membranous and around 5 mm in height, and the collar region has a pale yellow color.

This species has distinct populations that are both native and transplants from Europe, although there has been lots of mixing going on. But in general, P. arundinacea can become invasive in some wetland habitats, were its vigorous rhizome system allows it to exclude other plants and create the monotypic stands that I noticed in my lake.

I tried to remember whether this stand was here last year, and I don't believe it was. The pandemic perhaps has meant less maintenance of the surrounding area, and the species has suddenly become more visible. Nevertheless, it would be interesting to continue monitoring the stand and see whether it continues to spread and overwhelm the plants around it as time passes.

Phalaris arundinacea as an Ornamental Grass

Phalaris arundinacea (or Reed Canary Grass as it's known here locally) is a perennial C3 grass that has become invasive in certain wetland areas, where it forms dense monotypic stands as it spreads using its thick rhizomes.

The species has become important for various commercial uses. For example, its ability to grow in contaminated soil has made it a prime candidate for phytoremediation, and as a very fast grower it has also been used in biomass production.

The genus has also become infamous because of its ability to poison animals. P. arundinacea contains tryptamine alkaloids, and may also accumulate high levels of selenium. It has a history of poisoning cattle and sheep, and a related species was involved in the "drunken" behavior of kangaroos in Australia, which can end in the death of the animal.

The wild form of this species is green and very tall, reaching more than 2 meters high. But there are also several ornamental varieties which have become popular in the trade.

I bought P. arundinacea 'Strawberries and Cream' last Fall and planted it in an enclosed cement container. The grass thrived, and this Spring I had to transplant out some of the plants or it would have engulfed the Calamagrostis acutiflora (Karl Foerster?) that shared the enclosure with it.

I love the leaves of this grass, which are strikingly white and green, with some pinkish highlights. The species also seems pretty tough, and a few days after transplanting them out, the somewhat withered looking grasses had pushed out new culms.

New stems poking out soon after transplant

I expect they will soon spread quickly to fill the available space, hopefully before the heat of summer, as this is a cool season grass.

I love working with tough species!