120 POACEAE 



empty scales green, acuminate ; flowering scale about 1 cm. long, usually strongly papil- 

 lose-roughened, the callus about 4 mm. long and strongly pubescent with white appressed 

 hairs the awn 6-8 cm. long, spiral and very pubescent at the base, usually twice bent. 

 In dry soil, Texas. Spring and summer. 



2. Stipa avenacea L. Stems 3-8 dm. tall : leaf-blades involute-filiform, the basal 

 - as long as the stem, those on the stem 7-13 cm. long : panicle 1-2 dm. long, loose, its 

 branches lax and finally spreading : empty scales of the spikelet 8-12 mm. long ; flowering 

 scale shorter, black, hairy at the base, and with a ring of short hairs at the top, the awn 

 4-7 cm. long, bent, loosely spiral below. 



In dry woods, Rhode Island to Florida, mostly near the coast ; also in western Ontario and Wis- 

 consin. BLACK OAT GRASS. 



3. Stipa avenaceoides Nash. Stems 6-12 dm. tall, tufted, erect, slender : leaf- 

 sheaths glabrous ; blades involute-setaceous, glabrous, the basal ones about 3 dm. long, 

 those on the stem 2.5-12 cm. long : panicle simple, 1-2.5 dm. long, finally long-exserted, 



7-10 cm. long, pubescent below, spiral at the base, twice bent. 

 In dry sandy soil, peninsular Florida. Spring and summer. 



55. MUHLENBERGIA Schreb. 



Perennial or rarely annual grasses, various in habit, with flat or often involute leaf- 

 blades, and terminal contracted or open panicles, which are often slender, densely thyrsoid, 

 or almost spike-like, or diffuse with long capillary branches. Spikelets 1-flowered, small. 

 Scales 3 (or rarely 4), the outer 2 empty, persistent, membranous or hyaline, from minute 

 to almost equalling the third scale, keeled, acute, mucronate or rarely short-awned, the 

 second occasionally 3-toothed, the third scale somewhat rigid, convolute about the 2-keeled 

 hyaline palet and the perfect flower, at the apex entire or rarely 2-toothed, obtuse, acute, 

 mucronate to long-awned, the awn very often capillary, a fourth awned scale very rarely 

 present. Stamens usually 3, rarely fewer. Styles distinct. Stigmas plumose. 



Panicle contracted, its branches erect or nearly so : spikelets on short pedicels. 

 Empty scales at least % as long as the spikelet. 



Flowering scale not awned, but sometimes awn-pointed. 



Empty scales not awned, about % as long as the flowering scale, acute. 1. M. sobolifera. 



Empty scales long-acuminate, awn-pointed or awned. 



Empty scales about as long as the flowering scale, sharp-pointed, about 



3 mm. long. 2. M. Mexic.ana. 



Empty scales exceeding the flowering scale, usually twice as long, awned, 



about 5 mm. long. 3. M. racemosa. 



Flowering scale long-awned, the awn usually twice as long as the scale. 



Empty scales about equalling the flowering scale. 4. M. sylvatica. 



Empty scales %-% as long as the flowering scale. 5. M. tenuiflora. 



Empty scales minute, the first one often wanting. 6. M. diffusa. 



Panicle open, its filiform branches spreading or ascending : spikelets on very long 



capillary pedicels. 

 Stems erect, simple. 



Empty scales awnless, or awn-pointed : 



Awn of the flowering scale very short, rarely nearly equalling it in length. 7. M. trichopodes. 

 Awn of the flowering scale very long, often several times its length. 8. M. capillaris. 



Empty scales long-awned, the awns usually many times as long as the scale. 9. M. filipes. 

 Stems much branched and prostrate. 10. M. Porteri. 



1. Muhlenbergia sobolifera (Muhl.) Trin. Stems 3-9 dm. tall, erect, slender, 

 simple, or sparingly branched above : leaf -blades rough, those on the stem 1-1.5 dm. long, 

 2-6 mm. wide, those on the branches 2-8 cm. long and about 2 mm. wide : panicle 7-15 

 cm. long, slender : empty scales about 1 mm. long, the flowering one obtuse, scabrous, 

 the midnerve usually excurrent as a short tip. 



In rocky woods, New Hampshire and Massachusetts to Minnesota, Virginia, Tennessee and the 

 Indian Territory. Summer and fall. 



2. Muhlenbergia Mexlcaiia (L. ) Trin. Stems 6-12 dm. long, erect, or often pros- 

 trate, much branched : leaf-blades rough, those on the stem 1-1.5 dm. long, 2-6 mm. 

 wide, the branch blades smaller : panicle 5-15 cm. long, contracted : spikelets 2.5-3 mm. 

 long, the outer scales somewhat unequal, acuminate or short-awned, rough, especially on 

 the keel, the third scale acuminate, rough. 



In swamps and borders of fields, New Brunswick to western Ontario, North Carolina, Tennessee, 

 Nebraska and the Indian Territory. Summer and fall. 



3. Muhlenbergia racemosa (Michx. ) B.S.P. Stems 3-9 dm. tall, erect, usually 

 much branched : leaf-blades 5-13 cm. long, 2-6 mm. wide, rough: panicle 5-12 cm. long, 



