A New Invader: "Villainous" Ventenata and the Invasion of a Native Ecosystem

Wispy inflorescence of Ventenata dubia in foreground

In an earlier post I discussed how a group of winter annual grasses are spreading like wildfire in the vast Sagebrush ecosystem in the western part of the USA. 

This armageddon is destroying not only the pristine sagebrush shrubs which are critical to numerous animals like the sage grouse, but it also is significantly lowering the forage value of the land as palatable perennial grasses are replaced by the mostly unpalatable invasives.

In addition to earlier invasives like Bromus tectorum (cheatgrass) and Taeniatherum caput-medusae (medusahead grass), a newer species has been creating problems for land managers.

Distribution of V.dubia (EDDMaps, 2022)

Ventenata dubia was first discovered in Washington State in the early 1950s.  It is native to Southern Europe and North Africa, and it has rapidly spread at the rate of 1.2 million hectares per year (Native Invasive Plant Council, 2001), which means an area three times the size of Rhode Island is being invaded every year! It now is found in 11 states and 5 Canadian provinces, and land managers are frantically trying to slow its spread while it is still possible to do so.

Invasion by Ventenata dubia (photo credit: Novak et al)

Like other winter annual grasses that have caused havoc in the local ecosystem, V. dubia tends to create a so-called grass-fire cycle, where its presence increases the probability of fires, which in turn removes its competitors and allows it to overran the area. Another way that winter annuals can outcompete other plants is by germinating in fall or early winter, and senescing by mid-summer. This gives it a head start when it comes to taking advantage of the early spring moisture.

The grass-fire cycle of T. caput-medusae

This species has only recently arrived in Montana, and while botanizing in a local park in the city of Bozeman, I stumbled on a small cluster hidden amongst the other grasses.

On first look, the grass does not exactly inspire dread. Unlike T. caput-medusae with its alien looking inflorescence, or B. tectorum with its multitudes of sharp spear-like awns, V. dubia looks like a puny weakling that would roll over with the smallest puff of wind.

The sharp spear-like awns on B.tectorum is more intimidating than the diffused panicles of V. dubia

The inflorescence of this species is a spread out panicle, and its thin culm ends at the base with very shallow roots. But its outward appearance belies the heart of a bully. Some studies have shown that invasion by V. dubia in hay fields can result in losses of up to 50% (Prather and Steele, 2009), and like other hegemonic invaders, the diversity of native species suffers when it starts taking hold in an area (Jones et al, 2020).

Ventenata dubia whole plant. Notice weak shallow roots

Even more frightening is the fact that this new invader seems to be able to successfully dominate habitats that earlier invasives like T. caput-medusae and B. tectorum cannot. In one study researchers found that it had invaded dry forest, woodland, and forest scablands ranging from 1250-1665 m of elevation, places which previously had been relatively immune to winter annual grass invasions. This is important to note, because it means that the spread of this species has increased the overall footprint of invasive annual grasses in the already battered Western USA (Applestein et al, 2022; Tortorelli et al, 2020).

Very long ligule of V. dubia and the remnant dark red color of a node

I must admit I was lucky in finding the small cluster in that park in Bozeman, MT. The small size of V. dubia and its open diffuse panicles made it hard to distinguish from the masses of other dried grasses that dominated the landscape. 

But the specimens I found had panicles with horizontal branches that almost diverged at 90 degree angles, and the spikelets (the structure that holds the grass flowers) on the panicles were restricted to the ends of these branches, both of which are characteristics of the species. A quick check of the ligules (the membrane between the top part of a blade and the culm) also pointed to them as being V. dubia: the species has relatively long and large ligules. The very shallow roots of one specimen that I carefully uprooted is another characteristic of V. dubia, as is the dark nodes that were red earlier in its life cycle.

Dried spikelets of V. dubia with ribbed glumes and lemma with long awns.

Magnification also offered other clues as to their identity. The dried spikelets had no seeds, but each spikelet had a conspicuous lemma (a bract like  structure enclosing a flower) with a protruding awn, and the glumes (the two bracts enclosing the spikelet) were distinctly ribbed along the long axis.

The small infestation that I found may not remain so small, given the nature of V. dubia. But perhaps the much larger grasses around it will contain its spread, or perhaps it will be eradicated after its presence has been reported. Only time will tell.

As a last note, the spread of V. dubia is another major problem in an endangered ecosystem that many people don't even know about. But there is nothing "evil" or even "villainous" about the species, notwithstanding the title of the post. We tend to anthropomorphize other organisms when in the heat of emotion, but this species (like all the other "weedy" plants) is simply doing what it needs to do  in order to survive and prosper, with no malice in whatever green heart it has.

Literature Cited

Applestein, C., Germino, M.J. Patterns of post-fire invasion of semiarid shrub-steppe reveals a diversity of invasion niches within an exotic annual grass community. Biol Invasions 24, 741–759 (2022). https://doi.org/10.1007/s10530-021-02669-3

EDDMapS. 2022. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed August 26, 2022.

Jones, L., Davis, C., & Prather, T. (2020). Consequences of Ventenata dubia 30 years postinvasion to bunchgrass communities in the Pacific Northwest. Invasive Plant Science and Management, 13(4), 226-238. doi:10.1017/inp.2020.29

Stephen J. Novak, Massimo Cristofaro, Dorothy Maguire1, and Rene F.H. Sforza. The Invasive Grass Ventenata (Ventenata dubia): A New Threat for Nevada

Prather, T. S., and V. Steele. 2009. Ventenata control strategies found for forage producers.

Tortorelli, C, Krawchuk, M, Kerns, B. Expanding the invasion footprint: Ventenata dubia and relationships to wildfire, environment, and plant communities in the Blue Mountains of the Inland Northwest, USA. Appl Veg Sci. 2020; 23: 562– 574. https://doi.org/10.1111/avsc.12511

Cuddly Purple Cuties at Logan Pass

Anthers decorate the surface of its flowerheads. The "spikes" are the awns of each spikelet

We hiked the famous Hidden Lake trail in Glacier National Park's Logan Pass (in Montana, USA) a few days back, and the path to the lake  was through absolutely gorgeous and vast meadows.

Wildflowers were in bloom, and the land was covered in a riot of colors. The trail itself was a combination of raised boardwalks and packed earth, and along the sides I noticed grass flowerheads that I at first thought were from Phleum pratense (Timothy grass).

Meadows to Hidden Lake

But these were much smaller and shorter, and some had a dark color as they matured that I had not seen in the more common species.

When I started taking macro shots I discovered that the flowerheads were a beautiful purplish color under magnification. I typed it as Phleum alpinum, a circumboreal species that normally inhabits alpine and subalpine wetland environments. 

Phleum alpinum

This small cutie is a perennial that has awned glumes with one floret per spikelet. It loves less sandy soil, and seemed to form a healthy population up in the meadows of Logan Pass (elev 2000 m). Like many grasses, it seems unassuming at first glance. But a careful examination reveals a hidden beauty, which is made all the more precious by the work needed to uncover their allure.

If you ever visit the park (and I have to say it is one of the more majestic mountain destinations I have ever visited), then be sure to say hi to this cuddly purple blooming grass.

Peeking up from beside the boardwalk 

An Unexpected Insect Slaughter

Idyllic setting of the massacre

Note: Gruesome photograph below. The squeamish have been warned.

Praying mantis, spiders, and other predators sometimes lurk in flowers in order to ambush visiting pollinators. But because grasses are mostly wind pollinated, they are usually spared the drama of such interactions. 

But two days ago while going through the sights in Glacier National Park's "Going to the Sun" road (in Montana,  USA), I stumbled upon the grisly remains of some past feast.

Masses of Phleum pratense (Timothy grass) formed an impressive foreground to one of the many majestic mountains that decorate the park, and while taking photographs I noticed one particular inflorescence seemed to have unmoving insects on it.

The grisly remains of four insects 

When I took macro shots of the specimens, I was surprised to discover that they were the desiccated remains of what looked like flies. As noted in a past post, insects like hoverflies do visit flowerheads of grasses like Phalaris arundinacea (Reed Canary Grass) to collect pollen. 

Hoverfly  visits P. arundinacea

I've also photographed spiders lurking menacingly in the inflorescence of Cenchrus purpureus (Napiergrass).

Spider lurks in C.purpureus

In the case of P. pratense there are even studies that show native bumblebees collect pollen from this species, although whether or not they aid in its pollination is uncertain. 

Such visitations allowed some predator (likely a spider) to take advantage of this behavior in order to nab a few unwary victims. Fortunately, I'm no big fan of flies, but it was a gruesome find anyways.

Uncovering the lair of the sand centipede

I love my wife, but whenever I hike with her my botanizing is reduced to a minimal level.

So when I got the chance to explore a nearby trail on my own, I jumped at the opportunity and took my Nikon 3400 DSLR and  macro lens with me.

The beginning portion of the trail featured a wide sandy path, and on a previous excursion I had noticed really interesting critters that seemed to be slithering under the sand.

The trail covered with "sand centipedes"

It was the usual hot and humid Florida summer day, but this time I literally knelt to observe the little critters. The ground was really hot, but I was entranced by what I saw.

The long bodies of this grass formed sinuous patterns, the leaves half submerged in the sand and looking like the segmented legs of a centipede. I had to be careful not to keep stepping on one, although I knew that they were tough hombres that could take a few adversities and keep on ticking.

A half buried sand centipede as it crawls along the burning ground

Amazingly enough, many of them were in bloom or past bloom, and multitudes of flower and seedheads rose from the ground like the compound eyes of arthropods. They really did look like segmented critters!

Like a stomatopod with 2 eyes peering up from the sand

I identified the species as Eremochloa ophiuroides, which is a turf grass here in the southeast USA. It was introduced to the country in 1916 from China, and these specimens must have "escaped" from nearby lawns. Its common name in the area is "centipedegrass", which either refers to the overall body form or the segmented appearance of the inflorescence.

Inflorescence and stoloniferous culm that had been half buried in the sand

The species looks superficially like Stenotaphrum secundatum (which is called St. Augustine Grass here), but it is smaller and the inflorescence looks quite different.

Interestingly enough, I saw an ant going up and down the flowerheads, and I photographed what looked like aphids perched at the base of the rows of spikelets. The ant seemed to be attracted to the lumpish specks, and I was reminded of some recent research that hypothesized that  E. ophiuroides might be pollinated by various insects (Joseph et al, 2020).

Ant cultivating aphids on the inflorescence?

The spikelets themselves were quite small, but the silvery stigma and purple anthers were cute, and I spent some time getting macro shots of the structures. 

Purple anthers and silvery stigmas

I must have spent an hour or more in the heat and sun examining this population of "sand centipedes". I love tiny critters, and the small size of this species was quite attractive. True, it might only be a common turfgrass to some, but the exotic location that I found them in and the fact that they were in bloom captivated the explorer in me. Beauty lies all around us, even in the most common of things.  You just need to open your mind's eye and see.

Literature Cited

V Joseph S, Harris-Shultz K, Jespersen D. Evidence of Pollinators Foraging on Centipedegrass Inflorescences. Insects. 2020 Nov 13;11(11):795. doi: 10.3390/insects11110795. PMID: 33202733; PMCID: PMC7696019.

Life without Animal Pollinators: Why Grasses Embraced the Wind

Phalaris arundinacea grass inflorescence with white anthers and stigmas and foraging hoverfly.

Some people might be surprised to discover that grasses are flowering plants. That's because when they are compared to the large flowering structures sported by some other angiosperms such as orchids, grass flowers are miniscule indeed. They are not as large and showy as the flowers in some other plants because they are specialized for wind pollination, and thus have no colorful sepals or petals.

This reliance on wind for pollination is called anemophily, and it is in contrast with pollination via insects (entomophily) or vertebrates (zoophily). Around 10-12% of flowering plants are wind-pollinated (Ackerman, 2000), and such plants seem to have evolved specific traits that together make up a "wind pollination syndrome".

Imperata cylindrica inflorescence with purple anthers

Some of the traits in this syndrome are those which grasses exemplify, and include:

1. Having many pollen grains compared to animal-pollinated plants
2. Pollen grains are usually unornamented
3. Having many flowers compared to animal-pollinated plants
4. Petals are usually small or absent
5. Nectaries are absent.
6. Flowers are unscented
7. Styles and stigma are feathery.
8. Anthers with the pollen tend to have long filaments and are held away from the leafy structures to aid in wind dispersal
9. Plants tend to occur in open habitats where wind is plentiful.

Panicum virgatum inflorescence with reddish-brown anthers and pink stigmas

On first look, people might think that wind-pollination is less effective and more "primitive" than pollination by insects and other animals. Indeed, Charles Darwin himself expressed surprise that any plant should display this type of pollination, given how "wasteful" it seemed to him (Darwin, 1876).

But amazingly enough, not only is wind pollination the derived condition (that is, plants started out as being animal-pollinated, but then evolved wind pollination), but studies have shown that anemophily is about as effective as animal pollination when it comes to the percent of pollen that manages to be captured by receptive stigmas! (Harder, 2000).

Andropogon gerardii inflorescence with yellow anthers and purple stigmas

The impetus for the evolution of wind pollination in plants that used to have animals as pollinators has been hypothesized to be situations where animal pollinators become unreliable. For example, some areas that are newly-colonized by a plant may have scarce or absent animal pollinators. In this case, this "pollen limitation" can result in the evolution of wind pollination in the species. Preliminary studies have supported this notion and have shown that pollen limitation is less of a problem in wind pollinated plants than in animal pollinated ones (Friedman and Barrett, 2009).

Paspalum notatum inflorescence with blackish purple stigmas and anthers

In the case of grasses, the very attributes that partly define the family - high density populations that dominate and saturate the environment - may necessitate the use of wind for pollination.  The lack of enough animal pollinators to assure reproduction in these relatively dense populations have pushed the Poaceae to use wind as the primary mechanism for the dispersal of their pollen.

So the next time you get an allergy due to pollen, don't blame the plants. Blame the lack of animal pollinators! ;-)

Cenchrus spp inflorescence with yellow-orange anthers and purple stigmas

References

Ackerman JD. Abiotic pollen and pollination: ecological, functional, and evolutionary perspectives. Plant Systematics and Evolution. 2000;222:167–185.

Darwin C. The effects of cross and self fertilisation in the vegetable kingdom. 2nd edn. London: John Murray; 1876.  

Friedman, J., & Barrett, S. C. (2009). Wind of change: new insights on the ecology and evolution of pollination and mating in wind-pollinated plants. Annals of botany, 103(9), 1515–1527. https://doi.org/10.1093/aob/mcp035

Harder LD. Pollen dispersal and the floral diversity of monocotyledons. In: Wilson KL, Morrison DA, editors. Monocots. Melbourne, Australia: CSIRO; 2000. pp. 243–257.

The Many Faces of the Inflorescence of Bahia Grass (Paspalum notatum)

Paspalum notatum (aka Bahiagrass) is one of the species used as a perennial turfgrass here in the southeastern USA. It is also a forage grass, and is native to the southern parts of the American continent.

I was walking to the gym last week when I noticed that a lot of the wild grasses along the sides of homes under construction had the very distinctive inflorescence of this species rising up from the ground like little black penants. 

The two spike-like racemes of P. notatum bifurcate from a common point to form the rather attractive digitate flowerhead and seedhead. Each spikelet has two florets in it, one being fertile and the other sterile. 

The immature flowerhead is all green it seems, and as it develops you start seeing the black purple anthers and feathery stigmas (looking like the usual purple caterpillars) coming out of the spikelets.

P. notatum reproduction depends on the ploidy level of the individual plant. Those that are tetraploid (four sets of each chromosome)  are normally apomictic, with unfertilized but viable seeds being produced, while those that are diploid (two sets of chromosomes) are wind-pollinated and cross-pollinate. Seed production is high, and the species is highly successful in its distribution.

After fertilization, the spikelets seem to become darker colored, and after awhile dry out as light brown seeds, which are ready to be dispersed. 

I must admit, I really like this grass. Its flowerheads are distinctive and cute, and as a turfgrass it does not look as coarse and rough as Stenotaphrum secundatum (St.Augustine Grass), which is the other type of grass in our community.