90 POACEAE 



Plant green . s t e ms slender : leaf-blades 



rather sparingly pubescent. 102. P. pcdicellatum. 



Plant purplish : stems stout : leaf-blades 



densely pubescent. 103. P. malacon. 



Pubescence of widely spreading hairs. 



Stems, as well as the leaf-sheaths, densely 

 velvety pubescent, usually 6-8 dm. 

 tall. 106. P. scoparium. 



Stems, as well as the leaf-sheaths, papil- 

 lose pubescent with rather stiff long 



hairs, usually less than 4 dm. tall. 115. P. malocophyllum. 

 ** Middle leaf-blades of the main stem more than 1.5 cm. wide, some- 

 times 3-4 cm. in width, the base cordate and clasping. 

 Spikelets 3 mm. long or less. 



Leaf-blades glabrous, or sometimes ciliate on the margins. 



Spikelets 1.5 mm. long. 92. P. polyanthes. 



Spikelets 2-3 mm. long. 



Leaf-sheaths glabrous, or sometimes ciliate on the margin. 

 Basal leaf-blades smaller than those of the stem. 



Stems erect, even in the late state, sparingly branched: 



spikelets obtuse or acutish. 111. P. commutatum. 



Stems finally much-branched and prostrate, forming 



large mats : spikelets very acute. 110. P. Manatense. 



Basal leaf-blades usually very long, larger than those of 



the stem : 



Their margin naked. 113. P. Joorii. 



Their margin ciliate with long hairs. 112. P. mutabile. 



Leaf-sheaths, at least the lower ones and those of the 



branches, densely papillose-hispid. 114. P. clandestinum. 



Leaf-blades pubescent : 



Ovate-lanceolate: stems pubescent with short ascending 



hairs. 109. P. ovale. 



Linear: stems densely velvety pubescent with spreading 



hairs. 106. P. scoparium. 



Spikelets exceeding 3 mm. long. 



Pubescence on the stem and leaf-sheaths, if any, of soft weak 



hairs. 



Nodes naked : leaf-blades usually ciliate on the margin. 120. P. macrocarpon. 



Nodes densely barbed with spreading hairs : leaf-blades usu- 

 ally naked on the margins. 



Lower surface of the leaf-blades paler, glabrous. 121. P. Porterianum. 



Lower surface of the leaf-blades pubescent, as are also the 



sheaths and stems. 122. P. pubifolium. 



Pubescence on the stem and leaf-sheaths of coarse rigid hairs 



arising from manifest papillae. 119. P. RaveneUi. 



IX. LATIFOLIA. 

 Tropical plants represented in our range by a single species. 123. P. latifoUum. 



1. Panicum pro-stratum Lam. Stems prostrate and creeping, leafy, branching, the 

 summit ascending : leaf-blades ovate, glabrous or pubescent, ciliate on the margin near the 

 cordate-clasping base, usually 1-3 cm. long, sometimes larger : racemes 4-6, ascending, 

 one-sided, 1.5-2.5 cm. long : spikelets about 2mm. long, elliptic, glabrous, acute, the first 

 scale broader than long, truncate at the apex, the fourth scale transversely rugose. 



Along roadsides, Louisiana. Introduced from tropical countries. Summer and fall. 



2. Panicum obtusum H.B.K. Glabrous. Stems erect, simple, or branching at the 

 base, 3-6 dm. tall : leaf-blades usually erect, long-acuminate, 6- -22 cm. long, 2-6 mm. wide: 

 panicle linear, 5-15 cm. long, its branches appressed, one-sided : spikelets about 3 mm. long, 

 crowded, oval or obovoid, obtuse, turgid, in pairs, the one short- the other long-pedicelled, 

 glabrous, the first scale shorter than the rest, 5-nerved. 



In dry usually sandy places, Kansas and Colorado to Texas and Arizona. Also in Mexico. Sum- 

 mer and fall. 



3. Panicum mdlle Sw. Sterile stems 1-2 m. long, rooting at the nodes, the fertile 

 stems erect, 6-10 dm. tall or more, the nodes densely barbed : leaf-sheaths often overlap- 

 ping, papillose-hirsute : blades 1-3 dm. long, glabrous or pubescent, 7-15 mm. wide : 

 panicle 1.5-2 dm. long, its branches spreading or ascending : spikelets about 3 mm. long, 

 glabrous. 



In fields and along roadsides, Florida to Texas. Introduced from tropical America. Summer 

 and fall. 



4. Panicum paspaloides Pers. Aquatic. Stems 6-12 dm. long, usually clothed with 

 sheaths below : leaves glabrous ; blades 2.5 dm. long or less, 6-10 mm. wide: racemes 

 10-20, one-sided, the rachis broadly winged, appressed, 2-3.5 cm. long : spikelets about 2.5 

 mm. long, ovate, acute, glabrous, singly disposed in 2 rows, the first scale broader than 

 long and clasping the spikelet at its base, truncate at the apex, the fourth scale transversely 

 wrinkled. 



In shallow water, southern Florida and Texas. Also in tropical America, Asia and Australia 

 Spring to fall. WATER GRASS. 



