Monday, May 29, 2023

Psammophyte Beach Bum in a Barren Land: Sporobolus virginicus in Paracas, Peru

The area around the beach town of Paracas in Peru is pure desert, a desolate land with nary a plant beyond those weedy and cultivated critters that settled into the few human settlements in the region.

But close to the sea, various native plants clung to life against the all encompassing dryness. Precipitation is under 1 cm per year in the region (!), and the few areas with water are an oasis that attracts life.

One of the few plants that was not deliberately planted was Sporobolus virginicus, which thrived in large clusters next to the beach in town. It is called Seashore Dropseed in the USA.

This species is found all over the Caribbean and American coastal mainland, and is an extreme halophyte. That is, it is able to tolerate high salt concentrations, something that is advantageous in the saltwater drenched beaches where it loves to bum around. Some populations of this species can tolerate up to 1.5 M NaCl, which is 3 times the salt concentration of sea water!

In addition, the species is a psammophyte, which simply means that it can thrive in areas that are sandy and often unstable. This again makes it suitable for the changeable landscape of coastal beaches.

The grass itself is a short but tough looking critter, with stiff pointy leaves and a seemingly aggressive manner. Even its flowerheads are no nonsense structures bereft of any extraneous adornments. If this is a beach bum, then it's one that you don't want to tangle with. In fact, I saw one Paracas cluster sending ramets deep into  the midst of a neighboring plant, an act that seemed quite hostile. But appearances can be deceiving, and I have not seen any references that indicate the species has become invasive, or that it is even a particularly aggressive species in all the many places that you can find it.

It is also relatively easy to identify in beach settings, although one needs to see the flowerheads to differentiate it quickly from something like Paspalum vaginatum (which has the more typical Paspalum inflorescence). So the next time you are walking along a beach and see clusters of S. virginicus, think about its adaptability to both salt and sand, and marvel about the tenaciousness of this cosmopolitan beach bum.

Thursday, May 25, 2023

Rogue's Gallery of Exotic Grasses in Sacramento, CA

I was visiting a park yesterday in Sacramento (California, USA), and I chanced upon a scene that tickled my fancy.

Exotic and invasive grasses are not a rare sight in the state, especially since the so-called Golden Hills of the state are the direct result of the introduction of alien species - more on that in a later article. But by a fortuitous coincidence I managed to take a single photograph that had quite a few of the more infamous exotic grasses in it. 

 Included in the image is Taeniatherum caput-medusae, Aegilops triuncialis, Bromus diandrus, and Avena barbata/fatua. Click on the image to expand and try to see whether you can spot examples of each!

A couple of the specimens in the photograph are actually new to me. One was the beautiful (but invasive) Bromus diandrus., which is much larger than B. tectorum (cheatgrass).

Bromus diandrus
The other is Aegilops triuncialis, which is commonly called barbed goatgrass in the USA. 

Aegilops triuncialis

As an aside, in addition to seeing Aegilops spp for the first time ever, I also saw my first specimens of Bromus rubens (which has the common name Red Brome here in the USA). This species has an attractive inflorescence, but has proven to be quite invasive in desert shrub habitats and grasslands.

Bromus rubens

Bromus rubens

Wednesday, May 17, 2023

The Viking Syndrome: Why Grasslands (and Grasses) Became Wildly Successful

The open spaces, the open grasslands. Nothing could be better.

The overwhelming success of the Poaceae is not simply because of their well known habit of growing from the base, unlike many other plants. It is also because they exhibit traits that when taken together, researchers have termed the "Viking Syndrome", in honor of the ancient group that ranged far and wide, colonized many places, and had profound effects in areas where they landed.

One of the grasses I saw as I first stepped into the streets of Lima, Peru last month was a species that I had seen many times in many different places. There was no mistaking the distinctive digitate inflorescence, nor the wiry stoloniferous habit that was one factor that allowed the grass to become a fearsome competitor and so valuable to turf grass managers. I had seen the same species in New Jersey, in Florida, in several Caribbean Islands, and even in the Philippines. It was the common Cynodon dactylon (called Bermuda grass in the USA), and its success is one that is repeated time and time again in the Poaceae.

Cynodon dactylon in Peru
The discovery of this species in Peru was not even a surprise to me, because I have grown accustomed to seeing grass species that are extremely cosmopolitan in their distribution.

In an earlier article, I had summarized some of the reasons why grasses can be considered the most successful plant family in the world, even not taking into account their economic importance to humanity (e.g. rice, wheat, maize/corn, etc). 

Grasses are only the fifth most species-rich angiosperm family with about 12,000 species (Clayton et al., 2015). And yet ecologically, grasses are by far the most dominant plant familyAreas dominated by grasses cover up to 43% of the surface of the world (Gibson, 2009), and they are found in almost every ecological habitat, including Antarctica. Up to 37% of the land area of the USA is dominated by grasses! Entire ecosystems of animals and other plants depend on grasses for their continued health and existence.

In fact, although grasses account for only 3% of plant species on Earth, grass-dominated landscapes contribute 33% of global primary productivity, the amount of CO2 removed from the atmosphere every year to fuel photosynthesis (Beer et al., 2010).

The overwhelming success of the Poaceae is not simply because of their well known habit of growing from the base, unlike many other plants. It is also because they exhibit a suite of invasive traits that when taken together, researchers have termed the "Viking Syndrome," in honor of the ancient group that ranged far and wide, colonized many places, and had profound effects in areas where they landed (Linder et al, 2018). 

Specifically, grasses have:
  1. Efficient dispersal, 
  2. Rapid population growth, 
  3. Environmental flexibility 
  4. Flexible growth forms and phenotypic plasticity
  5. The ability to transform environments to benefit themselves
It is this combination of invasive traits that have allowed grasses to become the most successful plant family in the world today.

1. Efficient Dispersal

Grasses certainly are able to disperse far and wide. The method of dispersal after pollination varies among species, but include wind dispersal (anemochory), dispersal via animal coats
(epizoochory), and dispersal after ingestion by an animal (endozoochory). The ability of grass species to be efficiently dispersed is almost everywhere in evidence. 

For example, the dune grass Leymus arenarius was one of only 4 plants to appear during the first decade after the formation of the volcanic island of Surtsey in 1963 (Magnusson et al, 2014). Some grass species like Phragmites australis are also hailed as being perhaps the most widely distributed angiosperm in the world, with a range that extends from 70 degrees N to the tropics (Holm et al, 1977). 

The unit of dispersal is the inflorescence in whole or part. This "diaspore" includes the basic unit of the grass flowers, which are the spikelets. In many grasses these are frequently tiny and lend themselves to easy dispersal, but beyond that grass spikelets can show various modifications that enable them to be carried far and wide. The most common have long awns that help in wind dispersal, but some Cenchrus spp have sharp barbed "thorns" that can easily catch on animal fur or clothing.

The deadly spines of Cenchrus sp

In some others like Oplismenus undulatifolius the awns exude sticky droplets of liquid which can also adhere to passing traffic. Studies have found that a dog running through this grass could pick up 12000 or more seeds on its fur! People are also used as vehicles for dispersal, with one study showing that around 800 seeds adhered to fleece within 30 seconds, while even denim pulled in around 300 seeds within the same timespan (Beauchamp et al, 2013)!

The sticky awns of Oplismenus undulatifolius helps in its dispersaL

2. Rapid Population Growth

The ability to create enormous populations very quickly might be another trait that helps in their invasive success. Such rapid population growth can be the result of shorter generation times and early reproduction. This allows pioneer populations in new habitats to quickly overrun the area, and the shorter generation times also creates more rapid responses to directional selection.

Although no definitive study has been made to compare entire plant families, many grasses have extremely short generations times. For example, the weedy and cosmopolitan Poa annua can flower just six weeks after germination (Cope et al, 2009) . In the same way, the weedy and extremely invasive Bromus tectorum (called cheatgrass in the USA) also can flower within 5 weeks (Meyer et al, 2004).

Interestingly enough, the grass embryo might be one factor that contributes to their reproductive success. Unlike other plants in their order (the Poales), which consist of undifferentiated cells, the embryos of grasses is already differentiated into specialized tissues, including the root, a shoot with leaf initials, and a specialized structure called the scutellum, which digests endosperm and moves it to the rest of the embryo. 

Bromus tectorum can flower within 5 weeks of germination 

3. Environmental Flexibility

The Poaceae as a whole occupy all the environmental niches available to angiosperms. This ability is related to the amazing flexibility of the grasses when it comes to adapting to various environments.

For example, grasses have the ability to survive in the widest range of temperatures among plants, with Deschampsia antartica able to live down to -10 degrees C (with an optimum of 10 degrees), and Dichanthelium thermale able to tolerate up to 65 degrees C in the active geothermal areas of Yellowstone National Park. The evolution of freezing tolerance in the family in particular opened up vast areas of the colder parts of the world to colonization by the grasses.

Another example of the ability of members of the Poaceae to exist in extreme environments is the large number of halophytes in the family. Halophytes are organisms that are very tolerant of high salt concentrations, and the grass family is second only to the Amaranthaceae in the number of species that are halophytes (Moray et al, 2015), with studies indicating that salt tolerance evolved independently at least 70 times in the family (Bennett et al, 2013).

This ability to flourish in a wide range of environments is founded on various traits. As an example, the Poaceae exhibits all 3 different types of photosynthesis (C3, C4, and CAM)an attribute it shares with only 8 other plant families. Since the the type of photosynthesis used by a plant greatly influences where it grows best, this means the Poaceae is capable of existing in innumerable and varied environments. 

The Poaceae also have a strong propensity to 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. Such instances of LGT are an amazing way for a grass to "leap frog" the slower evolutionary pathways and suddenly acquire traits that allow them to survive in extreme and varied environments.

Muhlenbergia capillaris is a salt tolerant dune grass

4. Flexible growth forms and phenotypic plasticity

Grasses have evolved  a variety of growth forms that allow them to adapt to almost any situation or event, whether it be (a) continuous defoliation, such as by herbivores, (b) periodic defoliation, such as in seasonal climates, or (c) competition against other plants such as in forests.

In terms of vertical reach, most grasses are low lying organisms, but some species are tall, and form towering grasslands that reach high above the height of a man (e.g. Saccharum spontaneum grasslands). Bamboos are even taller, and their woody stems allow them to reach the height of mature trees in shaded forests.

In terms of horizontal spread, some grasses are bunch grasses that form tussocks, while others spread horizontally via stolons (above ground horizontal shoots) or rhizomes (below ground horizontal shoots) to form (for example) the typical lawns. This type of growth is controlled mainly by whether the species has intravaginal innovation (new shoots originate from axillary buds within the leaf sheaths) or extravaginal innovation (new shoots grow from axillary buds outside the leaf sheaths). In the latter case, the result is the ability of the grass to spread horizontally and blanket an entire area.

The vast majority of grasses also exhibit hemicryptophyte growth, which means that their buds are at or near the soil surface. This is one of the key mechanisms that allows grasses to withstand repeated defoliation via grazing or fire, and thus create climax communities that demonstrate an alternative biome state. This trait also means grasses do not necessarily need to maintain above ground structures during periods of extreme stress, such as droughts and cold, and it is the common reason that people assume grasses are so successful.

Bamboo sp (probably Bambusa vulgaris)

5. Transformation of Environments

The ability of members of the Poaceae to significantly transform their environment is perhaps the primary key to their success. By changing their surroundings, grasses create a hostile environment for other plants (including trees and shrubs) that may usurp their dominance, and even relegate them to minor components of the biota.

The way grasses transform the environment is rooted in their makeup. The reproductive fecundity of the grasses allows them to exist in numberless hordes, and their growth forms enable them to blanket entire habitats in contiguous swards, denying food, water and sunlight to competing plants. Their enormous populations, enabled via wind pollination, also allows them to use biotic feedback mechanisms that utilize fire and herbivore grazing to transform closed canopy forests into grasslands, and later maintain this alternative climax state

African Tropical Grassland (Savanna), by Gossipguy)

All the factors above combine to give to the Poaceae an invasive and aggressive quality that is perhaps unmatched in the plant kingdom. It allowed the grasses to range far and wide, colonizing all four corners of the world, and transforming vast lands into the wide open spaces that we see today. 


Beauchamp, Vanessa B.; Koontz, Stephanie M.; Suss, Christine; Hawkins, Chad; Kyde, Kerrie L.; Schnase, John L. (2013). "An introduction to Oplismenus undulatifolius(Ard.) Roem. & Schult. (wavyleaf basketgrass), a recent invader in Mid-Atlantic forest understories". The Journal of the Torrey Botanical Society. 140 (4): 391–413.

Beer, C., Reichstein, M., Tomelleri, E., Ciais, P., Jung, M., Carvalhais, N., Rodenbeck, C., Arain, M. A., Baldocchi, D., Bonan, G. B., Bondeau, A., Cescatti, A., Lasslop, G., Lindroth, A., Lomas, M., Luyssaert, S., Margolis, H., Oleson, K. W., Roupsard, O., Veenendaal, E., Viovy, N., Williams, C., Woodward, F. I. & Papale, D. (2010). Terrestrial gross carbon dioxide uptake: global distribution and covariation with climate. Science 329,

Bennett TH, Flowers TJ, Bromham L. Repeated evolution of salt-tolerance in grasses. Biol Lett. 2013;9:20130029-20130029

Cope, T., Gray, A. J., Tebbs, M. & Ashton, P. (2009). Grasses of the British Isles. Botanical Society of the British Isles, London.

Estep, M. C., McKain, M. R., Vela Diaz, D., Zhong, J., Hodge, J. G., Hodkinson, T. R., Layton, D. J., Malcomber, S. T., Pasquet, R. & Kellogg, E. A. (2014). Allopolyploidy, diversification, and the Miocene grassland expansion. Proceedings of the National Academy of Sciences of the United States of America 111, 15149–15154.

Gibson, D. J. (2009). Grasses and Grassland Ecology. Oxford University Press, Oxford.

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

Holm, LeRoy G.; Plocknett, Donald L.; Pancho, Juan V.; Herberger, James P. 1977. The world's worst weeds: distribution and biology. Honolulu, HI: University Press of Hawaii. 609 p.

Linder, H.P., Lehmann, C.E., Archibald, S., Osborne, C.P., & Richardson, D.M. (2018). Global grass (Poaceae) success underpinned by traits facilitating colonization, persistence and habitat transformation. Biological Reviews, 93.

Magnusson, Borgthor & Magnússon, Sigurður & Ólafsson, Erling & Sigurdsson, Bjarni. (2014). Plant colonization, succession and ecosystem development on Surtsey with reference to neighbouring islands. Biogeosciences. 11. 5521-5537. 10.5194/bg-11-5521-2014. 

Meyer, Susan & Nelson, David & Carlson, Stephanie. (2004). Ecological Genetics of Vernalization Response in Bromus tectorum L. (Poaceae). Annals of botany. 93. 653-63. 10.1093/aob/mch088. 

Moray, C., Hua, X. & Bromham, L. Salt tolerance is evolutionarily labile in a diverse set of angiosperm families. BMC Evol Biol 15, 90 (2015).

Friday, May 5, 2023

If scientific names became common (the case of Avena in Peru)

Avena fatua spikelets in Ollantaytambo, Peru

I eat a bowl of oatmeal everyday, and during our trip to Peru I tried to keep the same daily routine. Thus, we visited small grocery stores and super mercados in search of this food item, as well as water and various veggies. 

During one such trip I was startled to notice that the oatmeal packages in the store shelves were all labeled "Avena"!

Oatmeal for 1.30 soles!

Avena of course is the genus name of the oats, including the cultivated species Avena sativa. I have been boning up on my Spanish, and it was a small revelation to find out that in that language, oatmeal is known by the genus name of the plant.

Avena fatua in the Moras Salt mines in the Sacred Valley of Peru

This is I think similar in the way Spanish (and several other languages) use modifications of the species name of corn to designate that particular food plant. The binomial is Zea mays, and in Spanish the word for corn is "maiz", just like some other countries call it "maize".

Spikelets in A. fatua, some showing empty glumes

I've found this custom eminently laudable and something that would help (in a very small way) introduce laypeople to scientific nomenclature. Wouldn't it be interesting if rice is called "Oryza", or barley called "Hordeum"?

Maybe even fictional novels and movies could help spread the use of such monikers. I remember Stephen King, in his Dark Tower novels, uses the word "Oriza" to designate various items in the work that are associated with rice. These included a society of women warriors called "Sisters of Oriza", who wielded plate-like throwing weapons called orizas, and whose founder was named Lady Oriza. 

Seeds between dried glumes

Finally, speaking of  "Avena", during the trip one of the most common field grasses was of the genus Avena, likely Avena fatua. I saw this species all over the Sacred Valley area, including at the ruins of Ollantaytambo and Moray, as well as the town of Urubamba and the Moras Salt Mines. Even though this is considered a weedy introduced species, I've found the plant quite attractive, with its many drooping large and awned spikelets.

Just because it's weedy, does not mean it can't be physically attractive!