POACEAE 



85 



branches erect to spreading : spikelets, exclusive of the awns, 2.5-3 mm. long, the longer 

 awns 6-8 mm. long. 



In low woods and swamps, Georgia to Texas. Also in tropical America. Summer and fall. 



31. PANICUM L. 



Annual or perennial grasses, varying much in habit, with elongated or flat and broad 

 leaf-blades, and the spikelets in open or contracted panicles. Spikelets 1-2-flowered, lance- 

 olate, oblong, ovate to obovate or globose, obtuse to acute or acuminate. Scales 4, the 

 3 outer membranous, the first and second empty, the first usually much shorter than the 

 spikelet, sometimes minute, the third one empty or enclosing a shorter hyaline palet and 

 often also a staminate flower ; fourth scale shorter and usually more obtuse than the others, 

 chartaceous, glabrous and shining, at length indurated, enclosing a palet of similar texture 

 and a perfect flower. Stamens 3. Styles distinct. Stigmas plumose. 

 Herbs, varying in habit. 



Spikelets disposed singly or in pairs in one-sided racemes, the pedicels short. 

 Spikelets arranged in panicles but not disposed in one-sided racemes, the 



pedicels short or long. 



Basal leaf-blades long and narrow, similar to those of the stem : no rosu- 

 late tufts of leaves in the fall : spikelets lanceolate to ovate, usually 

 the former, acute to acuminate, rarely obtuse. 

 Spikelets manifestly tuberculate. 

 Spikelets not tuberculate. 



Basal leaf-sheaths round or but little flattened, not keeled. 

 Fourth scale smooth. 



Annuals or perennials, if the latter no rootstocks or stolons. 

 Perennial by long rootstocks or stolons. 



Rootstocks and stolons naked or with a few large scales : 



sandbinders. 

 Rootstocks, at least when young, and stolons covered with 



numerous small broad acute scales. 

 Fourth scale transversely rugose. 



Basal leaf-sheaths much compressed, broad, keeled, often equitant. 

 Basal leaf-blades commonly unlike those of the stem, ovate to ovate- 

 lanceolate : perennial by rosulate tufts which form in the fall at the 

 base of the stems : spikelets elliptic to spherical, usually obtuse, some- 

 times acute, never acuminate. VIII. DICHOTOMA. 



Much branched shrubs, with broad leaf-blades : spikelets large and turgid, the 



outer scales woolly-tipped. IX. LATIFOLIA. 



I. PASPALOIDEA. 

 Fourth scale of the spikelet smooth. 



Spikelets not ciliate with long hairs, the first scale % as long as the spike- 



let or less, excepting in no. 2. 

 Terrestrial grasses. 



Stems prostrate : leaf-blades short, ovate-lanceolate, spreading. 

 Stems erect : leaf-blades long and relatively narrow. 



Spikelets obtuse, turgid, the first scale very large, rounded at the 



apex, more than % as long as the spikelet. 

 Spikelets acute, the first scale small, acute at the apex, less than 



% as long as the spikelet. 

 Aquatic grasses. 



Spikelets singly disposed, about 3 mm. long, the first scale rounded 



or truncate at the apex. 



Spikelets in pairs, about 2 mm. long, the first scale acute at the sum- 

 mit. 



I. PASPALOIDEA. 



II. VERRUCOSA. 



III. CAPILLARIA. 



IV. HALOPHILA. 



V. VIRGATA. 

 VI. MAXIMA. 

 VII. AGROSTOIDEA. 



1. P. prostratum. 



2. P. obtusum. 



3. P. moUe. 



4. P. paspaloides, 



5. P. digitari&ides. 



6. P. ciliatissimum. 



Spikelets ciliate with numerous very long hairs, the first'scale narrow and 



acuminate, nearly as long as the spikelet. 

 Fourth scale transversely rugose : usually the outer scales of some or all of 



the spikelets with anastomosing veinlets. 

 Branches of the panicle terminated by a spikelet, no extension beyond 



them. 

 Spikelets 2.5-3 mm. long, broadly obovoid, obtuse or acutish, anasto- 



mosing veinlets numerous and prominent. 7. P. fuscum. 



Spikelets 4-6 mm. long, acute or acuminate, oval, anastomosing vein- 



lets few and faint. 



Spikelets about 4 mm. long, the first scale less than % their length. 8. P. fasciculatum. 

 Spikelets 5-6 mm. long, the first scale more than % their length. 9. P. Texanum. 



Branches of the panicle extending beyond the spikelets in an awn-like pro- 



jection. 

 First scale of the spikelet 1-nerved, or sometimes with a faint lateral 



nerve on each side. 10. P. Chapmanii. 



First scale of the spikelet 5-nerved. 



Spikelets 2.5 mm. long : leaf-blades usually short. 11. P. ramisetum. 



Spikelets 3.5 mm. long : leaf-blades usually elongated. 12. P. Reverchonii. 



II. VERRUCOSA. 



Spikelets about 2 mm. long, the tubercles not hair-bearing. 13. P. verrucosum. 



Spikelets about 3 mm. long, each tubercle bearing a short stout hair. 14. P. brachyanthum. 



