Legal note: I simply did not have the time nor the inclination to shrink the pics I uploaded for this post. They are all copyright me, 2017. Please don't use them or take them and sell them for profit without my permission to thousands of rabid, grass-appreciating people out there. Thanks.
Grasses and People
While the many of the organisms discussed on this blog are relegated to the periphery of our experiences (e.g. lichens, bryophytes), the grasses are front and center in our everyday lives. Grasses are estimated to cover about 1/3 of the land surface of the Earth(2), and are present in some form in every terrestrial ecosystem. Grasses are evolutionarily diverse, with more species than any plant family except Asteraceae and Orchidaceae which have the most and second most respectively. Grasses are also heavily used in a number of capacities by humans: where for some posts I've had to scour the literature to find any note of ethnobotanical interest for even entire phyla (e.g. lichens and bryophytes), most species of grass of any size have some use for cordage, basketry, food, construction (thatch, brick-making), animal feed, or any number of other uses. In modern times, most of our most economically important crops continue to be grasses. It is estimated that 13% of all land in Colorado is used for cultivating cereal grains and/or for hay production(2). These important crops, in turn, are nearly single-handedly responsible for the feeding necessary for modern (and ancient) animal husbandry(2).
Anywhere, CO. Grasses are hugely successful here and make up a significant percentage of our local flora. I have not been able to identify the species in this picture, although it appears to be one of a number of species which are referred to as wheatgrasses.
Cultural references to grasses in literary contexts abound: the Bible speaking of the "grass of the field" (Matt 6:30) as fuel for fires. The "Amber waves of grain" in the song America the Beautiful of course refer to any number of grass plants such as wheat and barley. Grasses have also been noticed by poets such as in "Grass" by Carl Sandburg. The most obvious poem citing grass is Walt Whitman's Leaves of Grass, in which he states that "I believe a leaf of grass is no less than the journey-work of the stars*." While mosses lie sullenly underfoot and other organisms such as mushrooms are viewed as fearful or bizarre, the grasses are exuberantly celebrated (rightly so) as one of the founding elements of human civilization.
*While Whitman was referring to the transcendental convention of seeing large truths and patterns in small things, he was on to more than he knew. Leaves of Grass was published in 1855; almost exactly 100 years later Fred Hoyle proposed the now widely accepted theory that the chemical elements are created by nuclear processes present in the life and death of stars. The carbon, nitrogen, and oxygen in the above leaf of grass are indeed the journey-work of the stars.
Morphology of Grasses
For a large and dominant group of plants, grasses are seldom identified by the lay person to the species level. This is because the correct identification of grasses demands its own terminology alongside what Weber (3) calls a willingness to "make measurements of very small things (p. 267)." Many of the structures necessary for the identification of grasses, while not hard to learn, demand accurate measurement and discrimination varying by only fractions of a centimeter. Indeed, Charles Darwin, Mr. Evolution himself, had this to say(4):
I have just made out my first Grass, hurrah! hurrah! I must confess that Fortune favours the bold, for as good luck wd [sic] have it, it was the easy Anthoxanthum odoratum:
nevertheless it is a great discovery; I never expected to make out a grass in all my life. So Hurrah. It has done my stomach surprising good.—
This is to say the scientist who was soon (in 1859) to integrate all extant knowledge of life and in so doing create the field of modern biology with his Origin of Species even had trouble identifying grasses. This is not to intimidate or discourage any of you who want to try, but more of an exculpation for myself for not wading into the minutia of grass identification. Try as I might, a working knowledge of the structures of grass flowers has not enabled me to get to the bottom of a dichotomous key even once, and I have found myself resorting to picture hunting in order to do most of the heavy lifting of identification.
Measure this, Darwin! The spikelets (flower clusters) of the "wheatgrass" from the first image. Each spikelet in the picture is <1cm long, and the accurate measurement of fractions of a centimeter can help to differentiate species.
The individual parts of a grass flower have their own special terminology which is well illustrated here, with a good example from an actual photograph here, and for good measure some line drawings here. Another (supposedly) useful diagnostic feature is the point of attachment of the leaves to the culm, known as the ligule; a sampling of ligules are illustrated here. Again, while these parts are not hard to learn in theory, I have found trying to actually measure all of the them and use them for keying out to be a tedious and confusing process. For the amateur, there is ultimately little better than hunting through pictures until something clicks: to do even this successfully with grasses you need a rudimentary knowledge of leaf shape and texture, habit of growth, habitat, and above all the morphology of grass inflorescences.
The most salient feature of a given grass tends to be its inflorescence. This is the first field feature that jumps out at one as they start to take note of the grasses in their environment: swirly, hairy, nodding, erect; the flower arrangements of Colorado grasses are rich in character and can make a useful jumping off point for identification. Worth knowing is that inflorescences of grasses tend to have a hierarchical organization: flowers (composed of tiny, measurable parts) cluster in many different numbers to form spikelets; spikelets are ordered on the inflorescence with or without petioles in distinctive arrangements. I have illustrated some of these arrangements which I have found useful below:
From left to right (red dots represent spikelets): spike, raceme, spicate raceme, panicle. While most of the grasses I've encountered in CO have an alternate orientation for flowering organs, there are many which have opposite arrangements too.
Noting the figure above, the most common orientations for flowers in local grasses are as follows:
- Spike: flowers (typically arranged in spikelets of more than one flower, although not always; from a casual vantage a spikelet appears to be more or less a single structure) arise directly from the culm (special grass-speak for "stem with a flower") without a discernible petiole.
- Raceme: flowers arise from petioles which attach to the culm.
- Spicate Raceme: flowers arise directly from the stem at axillary nodes of petioles and from petioles.
- Panicle: flowers arise from branching petiolate structures which arise from the culm. This is far and away the most common type of flower arrangement for grasses here in Colorado.
I have also provided some examples of inflorescences from pictures I have taken below; I was unable to find a picture of a species with a spicate raceme, but the three most important types are included.
At left: an unidentified grass with a raceme; it is difficult to see, but each flower in the photo is subtended by a petiole. While reportedly common, I have seen fewer grasses with this or a spicate raceme arrangement than with spikes or panicles. The "hairs" extruding from each flower are called awns; the awns of a given grass can be useful for identification and have important implications for how people and animals interact with it.
A panicle; note the many branches. Panicles are the most common inflorescence type for grasses in Colorado. The purple clumps at the end of each petiole are spikelets;each spikelet is made of multiple flowers.
A spike: note how none of the flowers are attached to the culm by a petiole. Numerous distinctive species of the plains and high desert sport this arrangement. This is also the flower arrangement of the most familiar of cereal grains: wheat.
Arrangements of flowering structures do oftentimes become more complex (along with their accompanying language); here is a non-comprehensive sampling courtesy of Grasses of Colorado:
Top row from left: panicle of digitate spicate primary unilateral branches; panicle of subdigitate spicate primary unilateral branches; panicle of verticilate spicate primary unilateral branches
Bottom row from left: panicle of alternate spicate primary unilateral branches; panicle of generally alternate racemose branches; alternately branching panicle at the disco.
Armed with a basic knowledge of infloresence morphology, an enterprising budding grass enthusiast can readily identify several local species of grass by sight without the benefit of a dichotomous key. I like to think of these as "sight grasses." Just as sight words are helpful as we start to learn to read the confusing, inconsistent words of English, the process of grass identification can be expedited by looking for helpful gestalts. I have treated my favorites of these below. Unless otherwise specified, information on these grasses has been gleaned from Grasses of Colorado.
Colorado Sight Grasses
Hordeum jubatum (Foxtail Barley)
H. jubatum grows in distinctive, highly visible clumps along roadsides and elsewhere.
Sunlight refracting through a forest of awns. H. jubatum has a highly appealing,
shimmering appearance when disturbed by wind.
The most prominent feature is the awns, which can be from 10 to 90 mm long. The sprays of awns give this grass a shimmering, almost iridescent quality as they scatter light passing over and through them. Some people will grow this grass as an ornamental for this reason, although I have not seen plants or seed for sale in any garden centers in the Denver area. The awns are also a tremendous source of headaches for ranchers and other keepers of livestock; each hair is tremendously long and also has minuscule barbs which can cause injuries to the nose, eyes, and mouths of animals. This means that having this native species growing on your land is not only a liability from a grazing perspective, but also that having H. jubatum contamination in cut hay can reduce its value.
A close-up of H. jubatum's awns (click to enlarge!). Looking closely you can
see tiny bumps on each awn; these are the barbs which cause
ranchers and animals so much grief.
Bromopsis inermis (Smooth Brome) syn. Bromus inermis
B. inermis panicles nodding in the breeze near Deer Creek Canyon park. I this instance it was the
primary grass next to a trail on an open arid grassland, although it seems equally at home in damp
riparian strips. B. inermis is considered invasive many places, although Colorado has not classified it as a noxious weed. Many of the articles I found referenced it out-competing prairie grasses, and while we certainly have prairies here,
it is possible that it is a bigger problem in states with wetter prairies. The fact that it is still planted as a pasture grass and soil stabilizer here in CO suggests that it is either less of a problem, or that the regulators have not caught up with the science!
Anthers are visible in this picture of another panicle. Many grasses will display bright yellow anthers when in full bloom, but the robust B. inermis is where I first took note of them. The styles of this grass are not visible in this photo; I have generally found it much easier to see grass anthers than styles.
The Smooth Brome is a solitary to loosely tufted perennial plant reaching heights of 1.3 meters, although most I have encountered are more on the order of 0.5M. Its spikelets are held in large, loose panicles which tend toward a nodding habit. Leaves are 15-40cm x 4-15mm and hairless or pilose (having a covering of soft hairs). It propagates both by seed and by tenacious, brittle, white rhizomes. My initial interest in this grass was a result of a hateful admiration for its resistance to eradication in my garden; its rhizomes are almost impossible to completely root out, and the slightest particle of surviving tissue will rapidly grow into a new plant (see caption under photo above for information on invasiveness/not). It is possible that this is why this plant is a popular choice for soil stabilization projects. It is also a popular pasture grass, providing excellent early season forage for livestock and for cutting to make hay.
B. inermis slowly covering the world. Tall stands like this are common
pretty much anywhere wild grasses are found.
Bromus tectorum (Cheatgrass) syn. Anisantha tectorum
This non-native is unambiguously unwelcome here. Cheatgrass is a winter annual, meaning that like the winter wheat which is grown in fields across the high planes, it germinates and does a reasonable amount of growing in the autumn. In spring, B. tectorum is leagues ahead of the native grasses which are just germinating, and it will rapidly take over large areas. One helpful identifying feature of this grass is that it tends to be one of the earliest-flowering grasses of the season.
Panicles of B. tectorum relatively early in the season (May). These well-developed flowering heads co-existed with other grass species nearby which were just beginning to bloom. Note the silvery color this grass lends to the scene.
To add insult to injury, cheatgrass is worthless as forage as soon as it has bloomed. As with H. jubatum, the awns can cause damage to the sensitive mouths of foraging animals. To add injury to injury, B. tectorum will quickly dry out and render large swathes of land which it invaded more prone to fires. The control and elimination of cheatgrass are much researched for these reasons.
Detail of a cheatgrass inflorescence. The spikelets in this image contain flowers
at this stage, not seeds.
The seeds of B. tectorum take on a stoplight palette which is beautiful in magnification.
The plant itself is actually rather attractive with nodding panicles of shiny spikelets held aloft by wispy culms ranging from 5cm to nearly a meter in height. Leaves are 4-16cm x 2-7mm and usually pubescent. Plants grow solitary to tufted. Each flower features three awns which are 1-1.8cm in length. As with H. jubatum, this grass has a pleasant optical quality to it when disturbed by wind; cheatgrass will make large areas look silvery and gossamer, while having a gilding effect later in the season.
Cheatgrass as it appears for most of the growing season after spring; golden, brittle,
and flammable.
Perspective: the golden background for this Helianthus annuus (i.e. common sunflower) is
actually nothing but rank upon rank of highly flammable cheatgrass plants; where this photo was taken
on the south slopes of North Table Mountain cheatgrass was dominant in large patches which would
easily have exploded into flame given a spark.
Achnatherum hymenoides (Indian Ricegrass) syn./formerly Oryzposis hymenoides
A. hymenoides is an instantly-recognizable native grass which has the distinction of being one of but a handful of species reported from all counties in Colorado. It has been reported by various authors to grow well in a huge variety of habitats and elevations; the common thread running through the reports seems to be environments with porous soil such as sand or shale. Where the previous species (cheatgrass) is maligned in virtually every way, A. hymenoides seems conversely to be blessed: It is an important source of forage for winter grazers as its vegetation apparently cures well; it has a long history of use by native peoples as a cereal grain food source; and it is a popular grass for use in native plant re-seeding efforts.
A. hymenoides starting to bloom near the Arkansas river in Buena Vista. Each widely
divided pair of flowers constitute one spikelet; to my knowledge nothing else out there looks like this. The
panicle is so cool I neglected to take any pictures of the plant itself: it's pretty much an easily-overlooked puff of grass with skinny blades.
The plant itself is a nondescript little tuft of grass with quite narrow blades (0.1-1mm wide) which then sprouts an unusual and distinctive inflorescence upon culms which range in height from 0.3-0.9M tall. The flowers are borne in a panicle, with each spikelet consisting of two flowers which are spread far from each other on long petioles. The petioles of A. hymenoides' panicle have an odd habit of twisting and turning so that up close it can create some really fantastic images. Each flower's ovary also has a pleasing plumpness to it; it is not hard to see how this plant was selected for a food source by hungry natives.
A closer look at a panicle; I find the twisting, weaving habit of this grass
to be absolutely hypnotic. Note the relative size of the grains in this
image compared to other species discussed thus far.
The inflorescence after the seeds have dropped; a blurry impression of the leaves can be
seen in the background. This image is one of the first I ever took of this species, years ago.
I found the ghostly randomness of the dry seed stalks to be fascinating.
Thank you for taking some time to learn about the wonderful world of grasses! My hope, as with all posts on this blog, is that it gives each of you dear readers a more granular (and dare I say, grainy?) appreciation of the plants all around us.
References
- Prasad, V.; Stroemberg, C.A.E.; Alimohammadian, H.; Sahni, A. (2005). "Dinosaur coprolites and the early evolution of grasses and grazers". Science. 310 (5751): 1177–1180. PMID 16293759. doi:10.1126/science.1118806.
- Shaw, R. B. (2008). Grasses of Colorado. University of Colorado Press: Boulder.
- Weber, W. A., & Wittmann, R. C. (2012). Colorado Flora: Eastern Slope. University of Colorado Press: Boulder.
- Darwin, C. (1855). To J. D. Hooker; June 5. [Letter]. Retrieved 7 July 2017 from https://www.darwinproject.ac.uk/letter/DCP-LETT-1693.xml
