HITCHCOCK AND CHASE NOKTH AMEEICAN PANICUM. 



305 



DESCRIPTION. 



Vernal plants commonly purple-tinged; culms in clumps of few to many, 40 to 75 

 cm. high, rather stout, erect, glabrous or sometimes softly (not crisp) puberulent; 

 nodes puberulent; sheaths shorter than the long internodes, ciliate on the margin - 

 and with a densely puberulent ring at the summit, otherwise glabrous or puberulent 

 between the nerves; ligules nearly obsolete; blades usually firm, spreading or ascend- 

 ing, 5 to 12 cm. long, 12 to 25 mm. wide, the lower and upper smaller than those of the 

 midculm, rather abruptly tapering to an acuminate apex and slightly narrowed 

 to the cordate-clasping base, glabrous on both surfaces or puberulent beneath or 

 sometimes also above, the margin ciliate at the base; panicles usually long-exserted, 

 6 to 12 cm. long, as wide or wider, loosely flowered, the axis glabrous or nearly so, 

 the flexuous branches spreading; spikelets 2.6 to 2.8 mm. long, 1.3 mm. wide, oblong- 

 elliptic, obtuse, softly pubescent; first glume about one-fourth the length of the spike- 

 let, triangular, acute or obtuse; second glume and sterile lemma barely covering the 

 fruit at maturity; fruit 2.2 to 2.3 mm. long, 1.2 mm. wide, elliptic, minutely umbonate. 

 Autumnal form erect or leaning, branching from the middle nodes, the portion of 

 the primary culm above the uppermost branch commonly falling away, leaving the 

 branch, with its shortened internodes, crowded, rather loose sheaths, scarcely or not 

 at all reduced blades, and hardly exserted panicle, as the apparent termination of the 

 primary culm; secondary branchlets crowded toward the summit, the reduced blades 



exceeding the partly included, much reduced 

 panicles; winter rosette appearing rather early, 

 the blades firm, ovate. 



This species is typically almost glabrous, 

 with stiff culms and firm blades, but puberu- 

 lence occurs rather commonly and is not found 

 to be associated with any other character. 

 The type of P. currani is puberulent through- 

 out and has somewhat broader blades than 

 common in P. commutation, but these charac- 

 ters are too variable to allow of separating this 

 form as a species. In some specimens the 

 culms only are puberulent, in others the 

 sheaths or the lower surface of the blades only. 

 The puberulence can not be coordinated with the wide blades. Some puberulent 

 specimens have ordinarily wide blades and other specimens with wide blades are 

 glabrous. 



Early autumnal specimens in which. the upper branch has replaced the terminal 

 portion of the main culm sometimes appear very different from vernal specimens, 

 owing to a somewhat unsymmetrical broadening of the middle of the crowded upper 

 blades. The type of P. subsimplex is such a specimen. A plant collected by Scribner 

 at White Cliff Springs, Tenn. (in Hitchcock's herbarium), shows several culms of 

 typical P. commutatum, the terminal portions widely divaricate, but not yet fallen, 

 and the upright branches with the unsymmetrically broadened blades as in the type 

 of P. subsimplex. 



A few southwestern specimens such as Hitchcock 1104, 1253, Langlois 39, and 41 in 

 part, Nealley in 1887 and Tracy 4577, differ in appearance from P. commutatum, having 

 rather slender culms and narrower blades and seem to approach P. joorii, but the 

 spikelets are not over 2.8 mm. long. 



Most of the Florida specimens are taller and more robust and have blades sometimes 

 as much as 20 cm. long and spikelets 3 to 3.2 mm. long. This form can not be satis- 

 factorily separated even as a subspecies, though extreme specimens differ sufficiently 



41616°— vol 15—10 20 



Fig. 344.— P. commutatum. From type speci- 

 men of P. nervosum Muhl. in Elliott Her- 

 barium. 



