Aquatic and Wetland Vascular Plants of the Northern Great Plains
63. Poaceae, the Grass Family
23. Poa L. -- Bluegrass1. Poa arida Vasey -- Plains bluegrass
Glaucous perennial 3-8 dm tall, with short to long rhizomes, the culms arising singly or tufted, erect, terete or somewhat flattened but not 2-edged, smooth. Leaf blades flat or involute-folded, 1-4 mm wide; sheaths glabrous, not keeled, closed only near the base; ligules 2-5 mm long, acute. Panicles usually contracted, sometimes rather open with the branches spreading-ascending, 2.5-15 cm long. Spikelets 3- to 9-flowered, often attractively tricolored owing to the glaucous glumes and the purple sides and whitish or bronzed tips of the lemmas, pale with age, 4-9 mm long, 1.5-3.5 mm wide; glumes ovate to ovate-lanceolate, obtuse to rounded at the tip, glabrous or scaberulous on the midnerve, somewhat unequal, the first glume 2.3-3.6 mm long, 1- to 3-nerved, the second glume 2.8-4.2 mm long, 3-nerved; lemmas 2.3-4 mm long, weakly keeled to rounded on the back, obtuse to rounded and somewhat erose at the tip, villous on the mid- and lateral nerves, pubescent between the nerves on the lower back, lacking cobwebby hairs at the base; anthers 1.2-2 mm long. Grain brown, obovoid, ca. 1 mm long. Jun--Aug. Alkaline wet meadows, shores and seepage areas, often abundant in such places, also drier upland sites; common in the c and w parts, less so in the e part; (Man. to B.C., s to IA, TX, NM and UT).
Three similar species of Poa are occasionally found in wet or moist, often alkaline habitats mainly in w part of our region. These share the glaucous coloration, narrow panicles and weakly keeled to rounded lemmas of P. arida and can thus be confused with it.
Most similar to P. arida is P. glaucifolia Scribn. & Williams, and like P. arida, P. glaucifolia is rhizomatous. The latter differs in its longer, more slender and more pointed lemmas mostly 3.5-5 mm long, usually less than 1/5 as wide in side view. The lemmas of P. arida are usually shorter and usually more than 1/5 as wide as long in side view.
P. juncifolia Scribn. and P. canbyi (Scribn.) Piper both differ
from the above in their tufted, generally nonrhizomatous habits. (P. juncifolia
sometimes has very short rhizomes.) P. juncifolia is distinguished
by its glabrous to scabrous lemmas, not having the pubescence on the nerves
and lower back like P. arida and P. glaucifolia. P. canbyi
is strictly tufted with lemmas that are short-pubescent or strigose on the
back, especially toward the base. A recent study by E. A. Kellogg (1985. Variation
and names in the Poa secunda complex. J. Range Management 38:516-521.)
suggests that P. juncifolia and P. canbyi are merely variants
of P. secunda Presl (formerly P. sandbergii Vasey) and should
be included under that name.
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