POACEAE 61 



Spathes narrow, long-acuminate, much exceeding the slender ra- 

 cemes : sessile spikelet 3-4 mm. long, lanceolate. 9. A, tetrastachyus. 

 Spathes broad, acuminate, equalling or shorter than the stout 

 racemes : sessile spikelet about 4.5 mm. long, broadly lanceo- 

 late. 10. A. Mohrii. 

 2. Racemes, at least some of them, entirely exserted from the spathes. the 



common peduncle thus visible. 

 Sheaths at the summit of the stem and also sometimes at the upper 



nodes much enlarged, crowded and imbricated. 

 All the flowering stems with enlarged upper sheaths ; lower sheaths 



shorter than the internodes, hence distant. 

 Basal sheaths and those of the innovations glabrous; enlarged 



sheaths in 2's or 3's, 3 mm. wide or less. 11. A. gracilior, 



Basal sheaths and those of the innovations densely hirsute ; en- 

 larged sheaths in 4's or more, 4-6 mm. wide. 12. A. Ettiottii. 

 Only some of the flowering stems with enlarged upper sheaths ; lower 



sheaths much exceeding the internodes, hence overlapping. 13. A. campyloracheus. 

 Sheaths not enlarged. 



Spathes exceeding 10 cm. in length : racemes long and lax, the inter- 

 nodes much exceeding the spikelets. 13. A. campylorachcus. 

 Spathes less than 8 cm. long : racemes short and stout, the internodes 



equalling or shorter than the spikelets. 

 Inflorescence much branched, branches much divided ; sheaths 



glabrous. 

 Racemes 1-2 cm. long, the spikelets about twice as long as the 



rachis-internodes. 14. A. brachystachyus. 



Racemes 3-4 cm. long, the spikelets equalling or little exceed- 

 ing the rachis-internodes. 15. A. Floridanus. 

 Inflorescence not much branched, the branches little or not at all 



divided. 



Sheaths glabrous ; racemes silvery white. 16. A. subtenuis. 



Sheaths hirsute ; racemes brown. 17. A. arctatus. 



b. Stamens 3. 



First scale of the sessile spikelet appressed-hispid between the keels, rather 



thin : sheaths sometimes pubescent. 



First scale nerveless between the keels, or if intermediate nerves occur, 

 not running the entire length of the scale : terminal hairs of the 

 internodes about twice their length. 18. A. argyraeus. 



First scale with 2 or 3 nerves between the keels, the nerves running the 

 entire length of the scale : terminal hairs of the internodes about 

 equalling them. 19. A. Cabanisii. 



First scale of the sessile spikelet glabrous and shining between the keels, 



firm : sheaths glabrous, and, with their blades, glaucous. 20. A. Scribnerianus. 



B. Pedicellate spikelet as large as the sessile, or larger, consisting of 4 scales and 



a staminate or rarely perfect flower. 

 Stems tufted, no rootstocks. 



Rachis-internodes of the racemes smooth : pedicellate spikelet staminate. 

 Outer 2 scales of the sessile spikelet more or less hispidulous all over : 



hairs on the internodes usually 2 mm. long or less. 21. A. furcatus. 



Outer 2 scales of the spikelet glabrous, excepting the nerves and also 

 toward the summit of the first scale : hairs on the internodes 3-4 

 mm. long, usually yellow. 22. A. chrysocomus. 



Rachis-internodes of the racemes strongly hispidulous : pedicellate spike- 

 let perfect. 23. A. Tennesseensis. 

 Stems from long horizontal rootstocks. 24. A. geminatus. 



1. Andropogon glomer^tus (Walt.) B.S.P. Stems 5-15 dm. tall, commonly 

 stout, the branches repeatedly and fastigiately branched, the lower ones somewhat elon- 

 gated but considerably shorter than the stem, thus forming a large oblong glomerate pan- 

 icle : leaf -blades 4 dm. long or less, 7 mm. wide or less, rough : spathes 2. 5-3 cm. long, 

 equalling or somewhat exceeding the racemes, smooth and glabrous, fastigiately crowded 

 at the summit of the stem and ends of the branches : racemes in pairs, 1-2 cm. long : ses- 

 sile spikelet 3-4 mm. long, the awn 10-15 mm. long, straight ; pedicellate spikelet want- 

 ing, or present as a subulate rudimentary scale. [A. macrourus Michx.] 



In low ground, Florida to Texas, New Mexico and Mexico. Fall. A form with the racemes usu- 

 ally more or less exserted from the apex of the narrow spathes which are tightly enrolled on the com- 

 mon peduncle of the racemes, is known as A. glomeratus tenuispdtheus Nash. 



2. Andropogon corymbosus (Chapm. ) Nash. Stems 4-10 dm. tall, rather stout, 

 from a little exceeding to twice as long as the basal leaves, the branches much divided, 

 the lower ones elongated and nearly equalling the upper, thus forming a corymbiform 

 panicle : leaf -sheaths keeled, those at the base much compressed and equitant, rough, often 

 more or less papillose-hirsute, especially the shorter and crowded ones of the inflorescence ; 

 stem-leaves with blades 3 dm. long or less, 5 mm. wide or less, rough : spathes very rough, 

 narrow, tightly enrolled around the common peduncle of the raceme which is densely his- 

 pidulous toward the summit and rather stout : racemes in pairs, more or less exserted from 

 the summit of the spathes, 2-3 cm. long : sessile spikelet 4-5 mm. long, the awn 12-13 

 mm. long, straight or nearly so ; pedicellate spikelet usually present as a subulate scale 

 12 mm. long. [\4. macrourus var. corymbosus Chapm.] 



In wet soil, District of Columbia to Florida and Mississippi. Fall. A form differing from the type 

 in having the spathes generally about equalling the racemes and few if any of them narrow and in- 

 rolled on the peduncles is known as A. corymbosus abbrerwtwt (Hack.) Nash. It ranges as far north as 

 Long Island, N. Y. 



