Accidental Epiphytic Beauty

Cenchrus setaceus

In December 2020, I discovered a grass that was perched between two large branches of a tree.

This made me start thinking about why the Poaceae, even though it's the 4th or 5th most speciose plant family, did not really have real epiphytic species. I discussed this mystery in that old post, and came to the conclusion that it probably has to do with the fact that grasses are creatures of the light and wind. True epiphytes are pretty much all animal pollinated, and tend to occur in forested areas.

But "accidental" grass epiphytes do occur, and I came upon an instance of this again when strolling around a neighborhood and canvassing the many ornamental grasses that graced its grounds.

Cenchrus setaceus inflorescence (white stigma and yellow anthers)

Varieties of Cenchrus setaceus (subfamily Panicoideae) were in evidence everywhere. They have beautiful cylindrical flowerheads that are tinged with purple, and I was gazing at a group of the ornamental C4 grasses when I was astonished to find that two of the specimens were literally growing from the trunk of nearby palm trees! Not only that, but both had flowerheads rising from their tops, a testament to the tenacity of the individuals.

Flowering accidental epiphyte (red arrow points to base of grass)

I examined one of them (see image below), and found that the shoots of the grass emerged from what I think are balls of moss that had adhered to the trunk. The moss piece felt hard to the touch and crumbled slightly when I handled it. So it is possible that seeds from this species had landed on the moss, and had been able to grow to maturity in such an unusual location.

Rooted in moss (Cenchrus setaceus)

Although Florida is considered a humid area, it does have a dry season when rain does not occur for many days or even weeks on end. But the air must retain enough moisture that allows not only mosses to survive on the exposed palm trees, but other more complex plants as well, such as the ferns and Tillandsia "air plants" that decorate many of the tree limbs here. In addition, this is a suburban community, and I have a feeling the various underground sprinklers that dot the landscape contribute some water as well. Finally, this species has been known to become invasive, and thus might possess some rugged attributes that belie its graceful appearance and allow it to colonize inhospitable locations.

But whatever the reason for their growth and survival, the two C. setaceus specimens certainly prove that the Poaceae might not have many true epiphytes, but it's not because of lack of trying.  

Mutual Assured Destruction: Revisiting an unlikely occupation

Flowering inflorescence of Imperata cylindrica, with orange anthers and purple stigmas

About a year ago, I wrote about how an invasive grass (Imperata cylindrica) started taking over an island in the parking lot of a building complex.

March 2022

A month or so after I posted that, the owner of the lot acted and when I next saw the lot in May, the entire island had been stripped of its vegetation and probably drenched in herbicides. They had pulled the trigger and given up on being able to selectively weed out the invasive, assuring the destruction of both the invasive grass and all the ornamental plants around it. Even so, I still saw a few blades of cogon grass poking out of the scene of destruction.

May 2022

I visited the area again last week, and the island was still bare, with even the two trees seemingly dead. The owners must have been repeatedly treating it in order to prevent any new regrowth of I. cylindrica. This repeated treatment and monitoring for a minimum of 2 years is a common practice when treating I. cylindrica infections, in order to ensure total eradication.

March 2023

I decided to revisit this old haunt because I had encountered another cluster of I. cylindrica that was weirdly similar to the situation in that parking island last year. In this new case, the invasive grass had grown on the mulched beds of two sidewalk Palm trees, and covered almost 20 m² at the bases of the trees. 

I. cylindrica cluster around the bases of sidewalk Palm trees

I had spotted it even from a distance because some of the ramets in the cluster were flowering, even though they had been cut close to the ground. When I came near I noticed that the white flowerheads were covered in orange anthers and purple stigmas.

I'm very surprised the cluster had avoided being eliminated by the groundskeepers in the neighborhood, who are usually quite liberal with the use of herbicides to keep most of the area weed free. Perhaps the presence of the palm trees, which are also monocots and thus susceptible to the same types of chemicals as grasses, had so far dissuaded them from acting.

I'm also slightly surprised that the thick mulch (tree bark) around the tree bases have had very little effect in preventing the spread of the invasive. The tenacity of this species can be admirable, even as the authorities curse its weedy nature, and I'll be sure to revisit the cluster occasionally when I can to see how it fares.

A nearby field of flowering I. cylindrica

Poaceae on the App: Grass Pro SA

Summary: It's a fantastic mobile app that went far beyond my expectations, and would be a great help for anyone who wants to learn about grasses in the southern part of Africa.

My first experience with a mobile app for grasses was for the grasses of Montana, and I found it useful and quite portable, since I brought my phone everywhere.

So when I heard about a new app called Grass Pro SA that focused on South African grasses, I immediately downloaded it from the Google PlayStore for my Samsung Android smartphone, and was immediately appreciative of its quality.

The home screen has a rotating background of very nice images of various grass inflorescence, and displays all the main sections of the app.

The Grass List is simply a long list of all the species in the app (there were 324 species when I tested it, but I assume they add to it over time), with the capability to search for specific species by name. The subsections within it contain more detailed info on each species, including nice images, the distribution, and personal sightings. More about this features later below.

Grass List

The Sightings section allows the user to submit and sync sightings of species that they find to the common database. This is a great feature that is not in the more basic Montana app, and allows users to participate actively in the building of the database.

Help and About gives very detailed information about using the app, as well as credits to those people responsible for its creation.

The Settings section is interesting, because it allows you set the language options for the species and common names. It was cool to be able to see what the common name of Imperata cylindrica is in Afrikaans for example (Donsgras), although most of the African common names seem to be missing (I tried Zulu and Xhosa).

Settings Section

The Location Section is one of the best features of the app, and it is not available in the free evaluation version. In the main page you can select whether you want to see grasses in your current location (I assume the app uses the phone GPS), from a selected area in a map, or whether you want to see all grasses in South Africa.

Location Main Page

I decided to try out the Select from map subsection. As you can see from the image below I selected an area in the southwest corner of Namibia (by just tapping at it), and the app immediately noted that it has records of 20 grass species in that area.

Finding species in a specific map location

I then tapped the search icon next to the label "20 grasses", and it brought me to a page where I was able to filter the results by specifying particular traits (see image below). The app allowed filtering using 8 different methods, and this was something that was really amazing to me. 

Ability to filter results via 8 methods

Not only can you filter via the usual structural traits, but you can also filter using such unusual ways as ecological information (grazing value, plant succession stage. ecological grazing status, weeds), and even via common uses! (see image below).

Filtering via common uses

Just to show how the process works, I went the route of using the major physical attributes to identity a specimen.

In this case, I got the option of filtering the 20 species using such features as plant height, inflorescence, spikelet, and leaf blade width (see image below).

Filtering using major or main plant features

I decided to go with inflorescence, and tapping it took me to another subpage, where I was able to select from various types, such as unbranched, panicle, and digitate flower spikes (see image below).

Selecting type of inflorescence

A small icon ("i") next to each image allowed me to go to a help and information page that went into detail about the inflorescence types, which was really helpful.

Info page about inflorescence types

After selecting unbranched, rounded inflorescence, I was taken to a list of 3 grasses that met my criteria.

Since I knew the species Cenchrus ciliaris, I picked that, and I was taken to a species profile page (see image below). This page not only contained full descriptions of C.ciliaris, but it also had several nice photographs showing the habit and fine detail of the species. In addition, it also displayed the full distribution of the species in southern Africa.

I cannot emphasize enough how cool this little mobile app was. It went far beyond my expectations, and a lot of work and effort must have gone into creating it. I highly recommend it for anyone who would like to identify and learn about the Poaceae in the southern part of Africa, and I hope similar apps are created for other regions of the world. 

I think my only minor gripe is that a lot of the African languages did not seem to have common names for the species, but both Afrikaans and English common names were included. The app was also a bit confusing when I used Current Location to try to see species near me. Since I am located in the USA, I thought that it would note down zero grass species nearby, but it seemed to indicate the presence of all 324 species. 

The evaluation version is free, but to see all the species in the database (324 species when I tested it), and be able to use the Location feature, the cost is an annual subscription of around US $10 (including tax).

A Flowery Conundrum: Allergic Beauty

Purple pollen bearing anthers in T. dactyloides

 It's that time of the year again when the world conspires to make me as miserable as possible.

This year, the slow change in global climate has resulted in an even earlier start to the allergy season, and pundits note that this will also stretch the season, something that is bad news indeed to countless allergy sufferers like myself.

Nevertheless, I like taking long walks in the afternoon, and while i was strolling along the landscaped sidewalks of our suburban community, I noticed how the rows of ornamental Trypsacum dactyloides (with the common name Eastern Gamagrass)  had started flowering.

The colorful purple anthers of this species are borne on white filaments, and when I stood in front of masses of the columnar spike-like inflorescence, my allergy suddenly took a turn for the worse. I started sneezing, and my eyes started to water somewhat.

Masses of anthers and filaments in the stamens of T. dactylodes inflorescence

My reaction was not surprising, given that some of the inflorescence were positively groaning under the weight of tons of pollen-producing anthers. 

If you remember from previous posts, this species is monoecious, with imperfect (or unisexual) flowers. Monoecious means that there are both male and female flowers on the same individual plant, and unisexual flowers have only either male or female parts. Most grasses have perfect flowers, where both stamens and pistil are present in a flower. 

The stamen is composed of anthers and filaments and is the male part of the flower, and the pistils are the female part of the flower. The stigma is the outermost portion of the female pistil, and in this species it is feathery in appearance, and also an attractive purple color. The stigma is involved in capturing pollen from the air, and its feathery appearance probably aids in this function.

A spider hides near a spent stigma and some anthers

In Trypsacum dactyloides, the male flowers are located on the upper part of the inflorescence, while the female flowers are near the base. I noticed that in some plants, some of the inflorescence have matured anthers, while in the rest of their inflorescence, it is the stigma which is showing first. In other specimens, both anthers and stigma are present at the same time.

Stigma of T. dactyloides

T. dactyloides is native to the area, and I love how landscapers have used it extensively in both commercial and residential properties here in Central Florida. Its dark green leaves and fascinating floral structures make it a very attractive addition to the scenery. But the same colorful flowers that I enjoy so much might also be a major contributor to the misery I feel every time Spring rolls around. Such is the paradoxical nature of life!

Stigma of T. dactyloides

The perplexing case of the spiral leaves

Spiral leaves

I was walking along a sidewalk path during one of my afternoon strolls, when I suddenly spotted a specimen that seemed to be a bit unusual. 

It was growing next to a construction area, and when I came closer to take a look at it, I realized it was because the plant had quite attractive spiral leaves.

Was this a genotypic attribute of the species or variety, or a result of some abiotic or biotic condition that was fleeting and would disappear when the condition was removed?

When I got home I immediately started googling for any other cases of this phenomenon. 

I did find a sedge that had really twisty leaves called Juncus effusus 'Spiralis', but the specimen I found looked different. There was also talk about how such a form seems to be prevalent in arid and windy regions, perhaps in order to resist the damaging effects of wind. Others hypothesized that such a form would be optimized for photosynthesis, since no matter the location of the sun, some part of the leaf would be placed to intercept its rays. The grass Danthonia spicata has twisted wiry leaves when dried, but these leaves were fresh looking and new, and not wiry at all, so I did not think it was this species.

Twisting or spiral appearance of the flag leaf can be caused by low temperatures (Lindsey et al, 2020)

I also found a paper that noted that the flag leaf of winter wheat (usually Triticum aestivum) can form a spiral when damaged by freezing temperatures (Lindsey et al, 2020, see image above). This effect was accompanied by yellowing or browning of the leaf, something which I did not see in the specimen.

Intrigued by this mystery, I took the specimen home with me, noting that the soil on which it lodged was extremely dry and hard. After placing it in a pot with potting soil, I watered it thoroughly and have been keeping watch on whether any new leaves would bear the same twisting phenotype, and whether the spirals on the older leaves would disappear. It would also give me the chance to identify the plant once it flowers or grows enough blades to be minutely examined.

More on this mystery later, I am sure.

Literature Cited

Lindsey, Laura & Alt, Douglas & Lindsey, Alexander. (2020). Freeze symptoms and associated yield loss in soft red winter wheat. Crop, Forage & Turfgrass Management. 7. 10.1002/cft2.20078. 

Ideas are like Grass

Osage Plains Prairie in Missouri, by Pat Whalen. To learn more about the importance of protecting original prairie in Missouri, and how you can get involved, please visit www.moprairie.org

I was scrolling through some posts about the Disney Plus TV show Willow when I came upon a quote that immediately resonated with me.

It is seemingly a direct quote from a novel by the well known author Ursula K. Le Guin, in her 1974 novel The Dispossessed.

I admit that I have never read any of her novels, although perhaps I now should, but the quote went thus:

It is of the nature of idea to be communicated: written, spoken, done. 

The idea is like grass. It craves light, likes crowds, thrives on crossbreeding, grows better for being stepped on.

I like the analogy, and her science is mostly correct as well.

Grasses are creatures of open habitats. Most despise the low lit interiors of forests. Grasses crave light, much as we do.

Grasses also tend to exist in numberless crowds. There are of course times when individual shoots are the norm, such as when environments are not ideal, or the flow of a species' history channel it into a solitary existence. But for the most part, grasses thrive in crowds.

Grasses share. Not only via the usual hybridizations, but also through fascinating processes like lateral gene transfer.

Her contention that a grass "grows better for being stepped on" is a bit more complicated. Trampling on first look is not that good for individual grasses. However, when viewed from the perspective of entire populations or grassland ecosystems, trampling can be very beneficial.

This is because some grasses and their ecosystems have evolved to benefit from grazing. For example, trampling by herds of animals can maintain grasslands by removing weeds (such as tree saplings). Herds can also help mulch the soil through the trampling of vegetation into the soil, and break hard soil crusts. So in that sense, Ursula K. Le Guin's contention that ideas and grasses benefit from trampling is quite tenable.

 Now, excuse me while I go and see whether I should buy one of her novels...

A Taxonomist's Conundrum (Or, A Poem on How I Lost My Hair Identifying ^$%^#^%!!! Grasses)

Thanks to Paul Marcum of the Facebook group "Midwest Graminoids - Grasses, Sedges, and Rushes, Oh my!" 

The Identification of Grasses

by H.D. Harrington

A grass can be “glumey” in more ways than one,

When its classification remains to be done;

You pull off the parts, and soon feel your age

Chasing them over the microscope stage!

You peer through the lenses at all of the bracts

And hope your decisions agree with the facts;

While your oculist chortles with avid delight

As you strain both your eyes in the dim table light.

You are left on the horns of quite a dilemma,

When you count the nerves on the back of the lemma;

Then you really get snoopy and turn each one turtle,

To see if the flower is sterile or fertile.

And then the compression, no problem is meaner —

Is it flat like your wallet or round like a wiener?

“How simple,” you think, “for a mind that is keen” —

But what do you do when it’s half-way between?

You probe and you guess how the florets will shatter,

For you know later on it is certain to matter;

You long for the calmness of labor that’s manual,

When the question arises — “perennial” or “annual”?

And that terrible texture, the meanest of all,

Is one of the pitfalls in which you can fall;

“Cartilaginous” maybe — or is it “chartaceous”?

Has even the experts exclaiming “Good gracious!”

Then you wail as you wade through the long tribal key,

“Oh, why must this awful thing happen to me?”

“Grasses are easy,” our teacher declares,

As he mops off a brow that is crowned with gray hairs!

(B) is the bent awn of the fertile floret that is being hidden between the enclosing glumes, and (A) is the rudimentary spikelet which sits on a pedicel. The axis segment that connected the unit to the next spikelet pair is labeled (C), and you can see at the top where it was detached from the raceme.

The use of open grasslands as a movie trope in epic quests (Willow 2022-2023)

The start of the quest (Willow 2022)

The new Disney Plus series Willow is a sequel to the beloved 1980s movie of the same name. It is an epic fantasy where the heroes go on a journey to rescue a prince from the clutches of a rising evil.

I had decided to watch the show during a particularly slow day. I was not expecting much from it, because I tend to like science fiction, but I was very pleasantly surprised when the series captivated me, and I now highly recommend it.

It was funny, deliberately cheesy, and somewhat campy in that the creators of the show introduced modern colloquialisms and music into the episodes. I also learned that the deceptively simple storyline was actually replete with symbolism and layers of complexity after watching a fantastic podcast called What the Force.  

Like many other high fantasy shows, the plot involves an epic quest. Interestingly enough, the director of the show depicted the start of the long journey by using wide angle shots of the protagonists on horses as they travelled across the open expanse of beautiful grasslands (the show was shot in Wales, and featured gorgeous scenery throughout the series). This scene was reminiscent of some other movies and shows that I had watched, and I realized that open grasslands are oftentimes used as a trope to characterize long epic journeys.

The quest continues (Willow 2022)

Movie or film tropes are a way of telling a story by using metaphorical language and scenes. They are used fairly often, and some common examples of cinematic tropes include the use of black for villains, and the frequent use of comedic sidekicks.

The use of open grasslands in Willow and in other shows made me think of why such landscapes are frequently selected to depict journeys or quests. I seldom see long epic journeys on fantasy films starting out with the protagonists hacking their way through the thick constricted underbrush of some deep dark forest.

A barrier between the open grasslands (Willow 2022)

When one thinks about the start of an epic fantasy quest in the movies, one cannot help but imagine that the journey will be filled with wondrous adventures and travels to exciting and far off lands for the protagonists. Thus, the director of such films needs to match his vision with the expectations of the avid watchers of the show, and the use of dark, cramped, and confined landscapes (such as the interiors of forests) would likely not entice them to ease happily into the story. 

Instead, he or she would opt for wide open spaces, panoramic scenery, and limitless vistas, attributes which are inherent to vast grasslands, as anyone who has ever stood in awe in the middle of old growth grasslands (or even grain fields) knows.

So the next time you watch high fantasy, such as LOTR, the Hobbit or Willow, see whether you can spot the ways the film producers use open ecosystems as a trope to entice and settle viewers into their equally expansive and sweeping world creations. 

The heroes meet up with the "Chosen One", Elora Danan (Willow 2022)

A new domain name (grass.keyapa.com)

Andropogon glomeratus (syn. Andropogon tenuispatheus)

You'll probably notice that I added the site to its own subdomain at grass.keyapa.com.

So from now on, instead of being at poasession.blogspot.com, Sejarah Poaceae will be at this new subdomain.

Just a little administrative note from the maintainer of the site.

It's Flowering Time for Imperata cylindrica!

It is January here and many of the Imperata cylindrica (cogongrass) stands are in flower.

Imperata cylindrica is known locally as Cogongrass here in USA, and it is a C4 member of the subfamily Panicoideae.

The species has a bad rep in many places. It is notorious for being listed as one of the top 10 weeds in the world, and its ability to compete and dominate its surroundings is well known, both in areas where it is an exotic, and even in its native range.

But a wind-blown field of flowering I. cylindrica is a beautiful sight.

The inflorescence at first are slim spikes of almost pure white, their pencil-thin shapes like missiles rising from the surrounding greenery. 

As the flowerhead matures it becomes more fluffy and rounded, the spikelets coming loose as the time for them to fly off to distant lands comes close. 

The callus hairs at the base of each spikelet are so fine and numerous that when the wind finally knocks one loose from the flowerhead, it usually drags others with it, so a somewhat roundish tangled ball of seeds is what one finds stuck to the ground once it alights. 

Seeds coming loose

Studies have shown that these seeds can be deposited by wind as much as 110 m away from the parent plant, with a possible total dispersion of up to 20 km away in open country!

Lift off!

The spikelets come in pairs, and each spikelet is 2 flowered, with the fertile and sterile flowers being enclosed in 2 similar glumes.

For a summary of spikelet components, you can read this short article.

I tried dissecting a spikelet using a pair of sewing pins, and I have to say it was quite difficult. Not only because it was so light and tiny (with a length of around 3 mm) that my breath alone caused it to be blown away, but because the callus hairs made it almost impossible to manipulate the tiny, fragile structure. It was a frustrating exercise.

Microscope image showing spikelet glumes surrounded by callus hairs

After repeated tries I finally managed to isolate some of the miniscule parts after cutting off much of the hairs. Under the pair of glumes, the fertile flower is protected by fragile looking and almost transparent lemma and palea, while the sterile flower has only the lemma.

Microscope image showing parts of spikelet (palea, stigma, and anthers/filament missing)

I separated out what looked to be the two lemma, as well as possibly the ovary with a long style. There were no anthers.

I have to say that after that arduous set of exercises, I have learned to really admire the fortitude and perseverance of grass taxonomists!

Rare inflorescence of Japanese Blood Grass (variety of I. cylindrica)

Finally,  I have to note that although the common varieties of I. cylindrica have an overall all-white inflorescence, an ornamental variety called Japanese Bloodgrass that I had in my garden in NJ had amazing looking purplish flowerheads. In this case, the numerous anthers were all fat and purple.

Rare inflorescence of Japanese Blood Grass (variety of I. cylindrica)

I. cylindrica is one of the few warm season grasses here in this semi tropical area that flowers during Spring. When it does flower it puts on quite a show, and I've gotten to look forward to its mass flowerings every year, much like I've eagerly anticipated the flowerings of the native Andropogon spp in Fall.

Family Ties - Grass Phylogeny I

Phylogeny of the Poaceae (Gallaher et al, 2022)

I bet we've been together for a million years, And I bet we'll be together for a million more...(from the TV series Family Ties)

Updated (2023-01-18) : Added table of subfamilies with number of genera and species.

I've discovered the joys of being able to identify some grasses to species. And I know how important such skills are in expanding one's knowledge. But there is just as much merit to studying the larger picture, and studying the way species are grouped together. This means that in order to truly understand a group of organisms, you have to study the relationships between the members of the group, as well as their evolutionary history.

This is where phylogeny becomes useful, because it is the study of how organisms are related to one another via evolution.

Our understanding of the relationships between grasses and their evolution has progressed in leaps and bounds. In many ways, the Poaceae are the most extensively studied plant family, due to the economic importance of some of its members (rice, wheat, corn sugarcane, etc), and this is reflected in the many phylogenetic and evolutionary studies of the group.

A few recent studies in 2022 in particular have expanded on the detailed evolutionary history of the Poaceae (Gallaher et al, 2022; Huang et al, 2022).

Some of the more recent discoveries:

• Grasses originated at the Early–Late Cretaceous boundary, with plastome studies finding a crown date of 98.54 mya (million years ago), and nuclear genome studies dating it to 101 mya. Both are consistent with fossil phytolith studies.

• Grasses probably first evolved in West Gondwana (Africa and South America).

• The ancestral habitat of the family was either the deep shade of the tropical forest understory or forest margins.

• Forest margins provided the transition zone before grasses moved to open habitats, and this move was independently evolved several times.

• Some grasses shifted back to closed habitats, but this is a lot less frequent than the move to open spaces.

• There are 12 subfamilies in the family Poaceae, which are grouped into 3 larger clades: the BOP, PACMAD, and the APP clades (much more on these groupings below). All the subfamilies are monophyletic, with the possible exception of one subfamily (Puelioideae of the APP).

• C4 photosynthesis evolved independently multiple times in the family, but only in the PACMAD clade, and only in 4 subfamilies within this clade: the Aristidoideae, Chloridoideae, Micrairoideae, and Panicoideae (the PACM of PACMAD). There is evidence it first evolved in the Chloridoideae 41-50 mya.

• Specialized freezing tolerance evolved in the Pooideae (BOP clade) in the Northern Hemisphere, and the Danthonioideae (PACMAD clade) in the Southern Hemisphere.

In order to more easily remember and thus understand the relationships between these subfamilies and the species under them, the different subfamilies are grouped into 3 major clades.

Each of the clades are monophyletic (ie. all the members of a clade are derived from a single common ancestor), and each clade name is an acronym of the names of the subfamilies within that clade. They are easily memorized using easy acronyms that you should remember.

1. APP
2. BOP
3. PACMAD

I'll skip the APP clade for later, as it represents the earliest diverging grasses that most people never encounter.

The two major grass clades are the BOP and the PACMAD groups, which represent more than 99% of the species in the family.

The BOP acronym stands for Bambusoidea (the bamboos), Oryzoidea (rice and its relatives), and Pooideae (many of the cold season turf grasses like Kentucky Bluegrass).

Now some may balk at trying to remember such tongue twisting subfamily names, but I use a trick that makes it somewhat easier. That is, every single subfamily name ends in "eae", and the 4 letters before that are always slight alterations of "oid", including "soid","coid","doid" or "zoid".

This makes it relatively easy to remember the names. For example, bamboos are BAMBU-zoid-EAE. And the rice subfamily is ORY-zoid-EAE. Finally, the turf grasses and other Northern Hemisphere cool season species are PO-oid-EAE.

Easier right?

Bamboo sp of the subfamily BAMBUSOIDEAE

The PACMAD clade is the other large grouping of grasses, and the acronym stands for the Panicoideae (e.g. many of the warm season grasses in USA tallgrass prairies like Andropogon spp), Aristidoideae (Aristida spp in Pine Savannahs in the Southeast USA), Chloridoideae (e.g. Muhly grasses), Micrairoideae, Arundinoideae (e.g. Phragmites), and the Danthonioideae (e.g. Pampas grasses of Cortaderia spp). The names can be easily remembered using the same rules as for the BOP clade:

PANI-coid-eae

ARISTI-doid-eae

CHLORI-doid-eae

MICRAI-roid-eae 

ARUNDI-noid-eae

DANTHONI-oid-eae 

Schizachyrium scoparium of the PANICOIDEAE

The relationships between the subfamilies and the time they diverged are summarized in the diagram below (mya= millions of years ago). The phylogeny is derived from studies of chloroplast DNA sequences in the paper by Gallaher at al, 2022, which has some differences from that presented by the equally recent Huang et al, 2022. 

Click here for image by itself.

As can be seen from the diagram above, the crown dates for the core grass subfamilies (BOP and PACMAD) range from 74 mya (million years ago) for the Oryzoideae, to 14 mya for the Aristidoideae. In the PACMAD clade, the Panicoideae is sister to the rest of the clade, while in the BOP, the Oryzoideae is the sister group to the Bambusoideae and the Pooideae.

However, in the Huang paper (which looked at the nuclear genome phylogeny), the Aristidoideae is sister to PCMAD, and not the Panicoideae, and the Micrairoideae is possibly sister to Panicoideae. The Puelioideae may represent two separate subfamily lineages.

It would be interesting to see how this discrepancy is resolved in future studies.

It's also interesting to compare the subfamilies with regards to the number of species and genera within. As can be seen in the table below (Soreng et al, 2017), the largest subfamilies are the Pooideae in the BOP clade (with 4126 species), and the Panicoideae in the PACMAD clade, with 3325 species.

Subfamily	Major clade	Genera	Species
Bambusoideae	BOP	136	1698
Oryzoideae	BOP	19	117
Pooideae	BOP	219	4126
Panicoideae	PACMAD	242	3325
Aristidoideae	PACMAD	3	367
Chloridoideae	PACMAD	121	1603
Micrairoideae	PACMAD	9	192
Arundinoideae	PACMAD	14	36
Danthonioideae	PACMAD	19	292
Anomochlooideae	APP	2	4
Pharoideae	APP	3	12
Puelioideae	APP	2	11

Here is a list of the major subfamilies and some selected species within each.

Bambusoideae (B in BOP)

These are the bamboos, which many people don't realize are also grasses. 

This subfamily diverged 54 million years ago, and probably originated in the Indomalayan region. All are C3 plants, and there are more than 1600 species in this group.

The bamboos are grouped into 3 groups, with the temperate woody bamboos at one end, and the tropical woody and herbaceous bamboos at the other.

Bamboos are thè tallest grasses in the world, with some species more than 30 m tall!

Example of the bamboos include Bambusa, Phyllostachys, and Dendrocalamus.

Bambusa vulgaris in the BAMBUSOIDEAE

Oryzoideae (O in BOP)

This subfamily contains about 117 species, and includes the two domesticated rice, the Asian species (Oryza sativa) and the African species (Oryza glaberrima). It originated 74 mya, most likely in the Afrotropics, and all the species are C3 plants. 

Rice is one of the most economically important plants, with its grains feeding billions of people everyday.

Oryza sativa in the ORYZOIDEAE

Pooideae (P in BOP)

This is the biggest grass subfamily, with more than 4100 species! It includes all the cold season turf grasses common in the USA, as well as domesticated food species such as wheat (Triticum spp) and oats (Avena spp). It originated 62 mya, most likely in the Palaearctic.

It is one of two subfamilies that has evolved specialized freezing tolerance. 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. Thus, the Pooideae dominate cool areas in the Northern Hemisphere. All are C3 plants.

Some example genera in this subfamily include Calamagrostis, Avena, Briza, Phalaris, Festuca, Lolium, Poa, Phleum, Triticum, Elymus, Hordeum, Leymus, Bromus, Nasella, Stipa , Taeniatherium.

Briza minor  of the POOIDEAE

Phleum alpinum  of the POOIDEAE

Taeniatherum caput-medusae  of the POOIDEAE

Phalaris arundinacea of the POOIDEAE

Bromus tectorum of the POOIDEAE

Panicoideae (P in PACMAD)

This subfamily is the largest in the PACMAD clade, and second largest in the Poaceae with more than 3300 species). It includes many of the warm season grasses, such as the major tall grass prairie species in the USA, as well as ferocious global invaders like cogon grass. 

It evolved 62 mya in the Afrotropics, and this is one of the subfamilies that dominate warmer areas in the world, with many of its members using C4 photosynthesis. In fact, this subfamily contains the majority of grasses with C4 photosynthesis.

It also includes some of the most economically important plants like maize/corn (Zea mays) for food, and Saccharum officinarum (sugarcane).

Genera in this subfamily include Andropogon, Microstegium, Imperata, Schizachyrium, Miscanthus, Saccharum, Sorghum, Zea, Paspalum, Cenchrus, Setaria, Spinifex, Panicum, Oplismenus, Digitaria, Dichanthelium, Melinis, Chasmanthium,Chrysopogon.

Panicum virgatum in the PANICOIDEAE

Andropogon gerardii  in the PANICOIDEAE

Oplismenus undulatifolius  in the PANICOIDEAE

Melinis repens  in the PANICOIDEAE

Paspalum fimbriatum  in the PANICOIDEAE

Imperata cylindrica of the PANICOIDEAE

Aristidoideae (first A in PACMAD)

This subfamily has around 367 species, and it is one of the four grass subfamilies that has C4 members.

 It originated fairly recently, an estimated 17 mya in the Afrotropics, and it includes some of the well known grasses that form the foundation of the Longleaf Pine savannas in the Southeastern USA, such as Aristida beyrichiana.

Aristida beyrichiana in the ARISTIDOIDEAE

Chloridoideae (C in PACMAD)

This subfamily evolved 55 mya in the Afrotropics, and includes many C4 plants. Along with the Panicoideae, it is one of the dominant grasses in the warmer parts of the world. The subfamily has around 1600 species.

Some of the grasses in my must-see list include species in this subfamily, including Swallenia alexandrae, which is found only in the Eureka Dunes in Death Valley National Park, CA, and the Orcutt grasses, which are endemic to ephemeral vernal pools in the same state.

Some genera in this subfamily are Muhlenbergia, Orcuttia, Eleusine, Cynodon, Chloris, Sporobolus, Swallenia, and Bouteloua.

Chloris virgata of the CHLORIDOIDEAE

Muhlenbergia sericea of the CHLORIDOIDEAE

Cynodon dactylon of the CHLORIDOIDEAE

Micrairoideae (M in PACMAD)

This is a relatively small family whose members are generally not known. It originated around 41 mya, probably in the Indomalayan region. It has around 200 species. It is sister to the Arundinoideae below.

Arundinoideae (second A in PACMAD)

This subfamily diverged 50 mya, probably in the Afrotropics. It only contains 36 species, but its most notable members are the well known genera Arundo and Phragmites.

Phragmites australis is a major invasive in some parts of the world, and might hold the title of the most widespread plant in the world. I have seen it in Florida and I have seen lots of it high north too. It is amazingly adaptable.

Phragmites australis in the ARUNDINOIDEAE

Arundo donax in the ARUNDINOIDEAE

Danthonioideae (D in PACMAD)

This subfamily diverged 51 mya, and contains around 300 species. I've always thought of them as the Pooideae equivalent in the Southern Hemisphere, although its sister group is the Chloridoideae.

Like the Pooideae, all species in this subfamily use C3 photosynthesis. And like the Pooidea, some members of this subfamily have independently evolved mechanisms for freezing tolerance. 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 most notable genus in this clade is Cortaderia, which includes the pampas grasses like Cortaderia selloana. 

Cortaderia selloana of the Danthonioideae

Knowledge about the relationships between members of the Poaceae, and how they are grouped together, allows us to derive general rules that govern the ecology and biology of these amazing organisms.  

So the next time you recognize or focus on a particular species, remember to find out where they belong in the subfamilies of the Poaceae. Are they in the PACMAD or BOP clade? What subfamily do they belong to, and when did this group originate? Which other subfamily is closest phylogenetically to that taxon? All questions that will surely help you understand that species in a deeper way. 

Chasmanthium latifolium of the PANICOIDEAE

References:

Gallaher, Timothy J., Peterson, Paul M., Soreng, Robert J., Zuloaga, Fernando O., Li, De-Zhu, Clark, Lynn G., Tyrrell, Christopher D., Welker, Cassiano A. D., Kellogg, Elizabeth A., and Teisher, Jordan K. 2022. "Grasses through space and time: an overview of the biogeographical and macroevolutionary history of Poaceae." Journal of Systematics and Evolution, 60, (3) 522–569. (The Biogeography of Grasses (Poaceae)) https://doi.org/10.1111/jse.12857.

Huang W, Zhang L, Columbus JT, Hu Y, Zhao Y, Tang L, Guo Z, Chen W, McKain M, Bartlett M, Huang CH, Li DZ, Ge S, Ma H. A well-supported nuclear phylogeny of Poaceae and implications for the evolution of C4 photosynthesis. Mol Plant. 2022 Apr 4;15(4):755-777. doi: 10.1016/j.molp.2022.01.015. Epub 2022 Jan 31. PMID: 35093593.

Soreng, R.J., Peterson, P.M., Romaschenko, K., Davidse, G., Teisher, J.K., Clark, L.G., Barberá, P., Gillespie, L.J. and Zuloaga, F.O. (2017), A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications. Jnl of Sytematics Evolution, 55: 259-290. https://doi.org/10.1111/jse.12262