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Grasses of the Edmonton Region, Part One

On December 13, in another of the ENPS’ Zoom presentation series, grassland ecologist Lysandra Pyle presented on the subject of the Grasses of the Edmonton Region. 


She observed that temperate grasslands and savannas are among the least protected plant communities in the world, with a large number of their species therefore at risk. 


Here in the Edmonton region most grasslands that are protected are semi-native, that is, a mixture of native and non-native species, in a matrix of tame pastures. They support a generalist grassland fauna. Historically, the City of Edmonton’s grasslands were probably of (plains rough) fescue; now, natural or semi-natural stands of grassland are pretty much confined to saline, sandy or badland soils, as loamy soils have been used for cropping. 


Apart from “prairies” at Nisku and Fort Saskatchewan, natural grasslands worth visiting include some on the sandy soils near Gibbons and Gibbons badlands along the Sturgeon River, Natural Areas such as Opal and J.J. Collett (near Lacombe), Pipestone Creek near Gwynne and, farther afield, at Donalda and Big Knife Provincial Park. 


When asked about the effects of grazing on grassland Lysandra replied that grassland health can be improved at low stocking rates. She noted that wicking of non-native smooth brome with herbicide can be done when the grass is taller than the surrounding ground cover in the spring. (Non-native smooth brome and Kentucky bluegrass are frequently major components of our remnant grasslands.) However, in the U.S. some land managers have concluded that certain non-native grasses are to be tolerated as better alternatives to some other weeds! 


The presentation was well-attended, suggesting there is considerable interest in grasses. Accordingly, and because we didn’t cover the grass family in the wildflower course that was offered a couple of years ago, I have decided to take a look at some of our commoner grasses in the next few WN issues. I should add that many grasses can be recognized easily by eye once they are known; for a confident identification, however, some examination of floral structure is required, for which a x10 hand lens is a necessity, and a dissecting microscope nice to have, as well, of course, as a key. Some grass manuals also provide a vegetative key, very useful if you are an ecologist who has to be in the field before the grasses, the majority of them summer-flowering, head out. However, I suspect most of us can wait until the grass flowers, at least to make our initial acquaintance with the species. Like almost all plants, grasses are faithful to their habitat and its nuances, so that a wetland or a woodland habitat, for example, will automatically reduce your options as to species. 

The pictures below indicate some of the terms you will need to know to use a key or follow a description.




Grasses of the Edmonton Region: Part 1.


The local bluegrasses or meadow grasses, Poa species. 


The genus Poa gives its name to the grass family as a whole, Poaceae (formerly Graminae). With over 70 species (including a few hybrids) in North America, and with extensive apomixis and polyploidy in the reproductive system, Poa species are not easy to distinguish from one another. They cannot, however, be ignored: our most abundant and obvious grass is a Poa. Kentucky Bluegrass, Poa pratensis, is well known as a lawn and pasture grass in cooler regions of North America, as well as an invasive weed to those of us trying to grow native plant gardens or manage a “prairie” remnant. Of the 23 Poa species in Alberta, 12 are alpine (including two that are also montane), of which half are rare; and six are non-native, including three species that are common locally and need some description: Poa pratensis, Poa annua and Poa compressa. This leaves five species of which two are decidedly southern grassland denizens, meaning there are only a further three species with which we need only to be concerned with in the Central Parkland region, all native: Poa palustris, P. interior and P. secunda.


One character, although not always easily recognized on some of the finer-leaved plants, that defines all Poas is that the leaf tip is prow-shaped, as in the prow of a boat. The inflorescence is a panicle, that is, with branches bearing the stalked spikelets; these are usually flattened from side to side and consist of two to several florets borne on a short stalk above the two basal bracts or glumes. In many species there is a tuft of cobwebby hairs at the base of the lemma, so that its presence or absence is an important distinguishing characteristic. The distribution of hairs or otherwise on the veins and between-vein areas of the lemma is also significant. (The lemma and palea are the two bracts that surround the reproductive parts (anthers and pistil) proper in the floret.) 


Kentucky bluegrass, Poa pratensis, is rhizomatous, and this character, along with its broad, flat, spreading basal leaves makes it an excellent sod grass, widely used in cooler parts of the world as a lawn and pasture grass, although it is native only to the temperate regions of Eurasia. (Over 60 commercial cultivars have been developed.) It grows 30-80 cm tall, its stems usually in tufts, has flat leaf blades 2-4 mm wide, and pyramid-shaped inflorescences (panicles) whose lower branches are usually in a whorl of five. The spikelets are flattened, 3-6 mm long and consist of 2-5 florets. The lowermost lemmas in each floret are 2-4.6 mm long, keeled, and distinctly nerved; the keel and the marginal veins, particularly, bear white hairs. The base of the lemma (or callus) has a tuft of cobwebby white hairs. As can be seen in the picture, the upper portions of the lemmas are often purplish, with a transparent (hyaline) tip. When a large patch of the grass is in flower, these lemma tips give the sward a bluish hue, hence the North American name of Kentucky bluegrass. (It was widely imported into the eastern U.S. states during settlement, as a forage grass.) Its name in Britain is smooth meadow-grass. 


The plants that we commonly encounter are the non-native subspecies, subsp. pratensis. However, two native subspecies exist, although they are apparently uncommon: ssp. alpigena and ssp. agassizensis. Whether it would be possible to replace the non-native, introduced subspecies with native ones in our grasslands is an intriguing question and one that I believe requires further study.



Poa pratensis with panicles not yet fully expanded, at Bunchberry Meadows on 2021-06-11. The prow-like tips of the leaf blades can be observed in this picture.


photo by Stefan.lefnaer, of spikelet of Poa pratensis. Note the upper and lower glumes, the 4 florets with purple and transparent (hyaline) tips, and in the third pane the keel on the lemma and the cobweb of hairs at the base.


Canada bluegrass, Poa compressa, is also a non-native perennial that is strongly rhizomatous, sending up solitary shoots to 60 cm from long rhizomes. It shares a lot of features in common with Poa pratensis, especially qualitatively, and so can be hard to distinguish from the much commoner species. However, its narrower, more congested panicle, with 1-3 erect and shorter branches, gives it a different look that may attract attention. The branches bear very short, stiff bristles, a character known as scabrous, whereas those of many pratensis specimens are smoother. Its slender, ovate spikelets, which tend to have more florets (up to 7) than pratensis, also add to the congested appearance of the panicle. However, it is the easily observed flat (as opposed to cylindrical) stem that is its main distinguishing feature. It is often sown for soil stabilization and locally it occurs occasionally on disturbed ground that has been cultivated. Recently it has appeared in numbers in the planted eco-islands in Wagner Natural Area in a field that was last cultivated with timothy grass. 


Flat-stemmed or Canada bluegrass collected in Wagner Natural Area, 2020-09-04; left, whole plant minus roots;


showing slender-ovoid spikelets, mostly with seven florets, and flat stems.

Annual bluegrass, Poa annua, is best recognized by its habitat, and its low, sprawling habit. (Erect flowering stems grow up to 20 cm tall.) It occurs commonly along wet, often muddy, trails and in places like boat ramps, as it appears resistant to trampling. It is native to Eurasia, but has spread throughout much of the world. An annual as it name indicates, it grows from a tuft of fibrous roots, although it can occasionally also produce stolons. The panicles range from 1-7 cm long and have 1-2 smooth branches at each node. The lemmas differ from those of the previous two species in having no web of hairs at the base, although the keel, marginal veins and often the lateral veins are white-hairy. Annual bluegrass is among the earliest of our Poas to flower, often showing ripe anthers during the May Count at the end of May. By contrast, Kentucky bluegrass reaches peak flowering around mid-June.  



Left, mounted specimen of annual bluegrass, collected at Lynn Lake, Manitoba 1974-07-24;


right, specimen of inland bluegrass, Clyde Fen Natural Area, collected 2003-07-27.

Inland bluegrass, Poa interior, is another tufted grass, lacking rhizomes or stolons, but is a perennial, native to North America. It produces several stems in the clump, up to 80 cm high. The panicles can be long, up to 15 cm, and are lance-shaped to ovoid with 2-5 branches up to 8 cm long at each node. Although the range of spikelet size is similar to that of Poa pratensis, the spikelets contain only 2-3 florets. The web of hairs at the base of the lemmas is scant; the keels and marginal veins are short-hairy. The lemma tips are usually bronze-coloured. This species prefers drier soils, and locally seems to be most common on sandy soils, although often with some shade. Flora North America (page 576) notes: “It is sometimes difficult to distinguish from P. palustris (p. 574), but differs in having lemmas with wider hyaline margins and straight or gradually arched keels, a densely tufted habit, and scantly webbed calluses.”



Left, herbarium specimen of Poa secunda from saline area at Van Es Prairie, near Cooking Lake, 2004-07-05;



right, close up of part of panicle of a specimen from Medicine Hat, 2003-06-22.

Fowl bluegrass, Poa palustris, is a tall (to 120 cm), tufted, loosely growing perennial grass that is also frequently stolon-bearing. It is a common grass of wet places, marshes, shores, wet meadows and ditches. The panicles are long, up to 20 cm, and open at maturity with whorls of 2-9 wide-spreading branches. There are 2-5 florets per spikelet, but the lemmas are small at 2-3 mm. The lemma callus is sparsely to moderately webbed and the keels and marginal veins are short-hairy. The lemma tips are characteristically bronze-coloured, incurved and blunt, with narrow hyaline margins. Poa palustris is native to cool-temperate North America and northern Eurasia, but has been introduced into parts of North America, often for soil stabilization and waterfowl feed. It resembles Poa interior but can be distinguished from it by its habitat, looser growth habit, better developed webs and narrow hyaline margins on the lemmas


Left, alpine bluegrass specimen from near Nordegg, 1981-06-28, showing short, broad basal leaves with prow tips, and short stem leaves;


right, panicle in flower showing typical Poa-type spikelets with keeled glumes and lemmas, at Prospect Creek, Cadomin, 2010-07-29.

Sandberg’s bluegrass, Poa secunda, is a native, tufted perennial growing 15-120 cm tall. Leaf blades are up to 3 mm wide, and can be flat, folded, or inrolled. The panicle can reach 25 cm in length, and is narrowly lanceolate to ovate, contracted except at flowering time, with 1-3 branches of varying lengths per node. The spikelets are 5-10 mm long with 3-5 florets; they are somewhat rounded in contrast to the distinctly flattened spikelets of most other Poas, and this is a distinguishing feature. The lemmas are large at 3.5-6 mm and have a wide hyaline border; they are weakly keeled, the keels and marginal veins and the spaces between the veins bearing hairs. The web is lacking. In our area, the species is mostly found in saline wetlands or areas of solonetzic soil, but it is more common further south and occupies more diverse habitats. It is a highly variable species that includes four taxa that were recognized as separate species in Flora of Alberta (1983): P. canbyi, P. juncifolia, P. nevadensis and P. sandbergii. Two subspecies of P. secunda are all that are now recognized, subsp. juncifolia and subsp. secunda. Complicated, eh? 


As I’ve mentioned, distinguishing Poa species is not easy, but hopefully readers will now be able to recognize the genus Poa, at least. Full descriptions and images of all these species can be obtained by searching Flora North America and the species scientific name, or from other online sources. 


I am inclined to mention one other species, not local, that demonstrates the typical characteristics of Poa very well. It is alpine bluegrass, Poa alpina, which is so common that it will be seen by all visitors to the mountains, north and south, and thrives at montane altitudes low and high.



References

Kershaw, Linda and Lorna Allen, 2020. Vascular Flora of Alberta: An Illustrated Guide. Self-published. Kindle Direct Publishing.


Moss, E.H. 1983. Flora of Alberta. 2d ed. edited by J.G. Packer, Toronto, University of Toronto Press. 


Flora of North America. Treatment of Poa occurs in volume 24. To obtain online information, search on scientific name followed by Flora of North America. 


Key to species described above, modified from Kershaw and Allen:


1a. Plants annual; low plants of wet, disturbed areas, e.g., paths, trampled shorelines;

usually in flower by the end of May/early June………………………………………….. Poa annua


1b. Plants perennial; habitats various; flowering mid-June to July…………………………… 2


2a. Lemmas with white, cobwebby hairs at base……………………………………………………… 3


2b. Lemmas lacking white, cobwebby hairs at base or hairs small and sparse………….. 5


3a. Plants with rhizomes…………………………………………………………………………………………. Poa pratensis


3b. Plants without rhizomes…………………………………………………………………………………….  4


4a. Plants usually 40-100 cm tall, in loose clumps, panicle 13-30 cm long; web well developed; plant of wet habitats, e.g., wet meadows, swales…………………………. Poa palustris


4b. Plants 20-30 cm tall, in dense clumps; panicle 5-15 cm long; web scant; plants of drier habitats ………………………………………………………………………………………..Poa interior

5a. Stems conspicuously flattened; plant strongly rhizomatous; plants of disturbed habitats; non-native …………………………………………………………………………………………………….  Poa compressa


5b. Stems not flattened, cylindrical; plant tufted; native plants of moist, saline habitats…Poa secunda


I usually look first for rhizomes (a grass forming patches is indicative of the presence of rhizomes or stolons) which if present would allow separation of Poa pratensis and Poa compressa off from the other species without the need to look at floral morphology. These two species could then be separated by the flattened stems of Poa compressa. The presence of a conspicuous lemma web would confirm the much more common Poa pratensis







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