GRAMINEAE (GRASS FAMILY) 97 



larger, glumes many-nerved ; sterile lemma subrigid ; 

 fertile lemma and palea much indurated, acuminate, 

 m;in:ins of lemma neither hyaline nor inrolled. Erect 

 annuals or perennials with flat leaves. (Name from 



iros, doubly fruit-bearing.') 



1. A. Piirshii Kuntli. Annual ; culms erect, branch- 

 ing, 3-6 dm. high ; sheaths and blades coarsely hispid ; 

 terminal panicle contracted ; spikelets about 4 mm. long ; 56. A. Purshii. 



fertile spikelets solitary, about 6 mm. long, at the ends sterile spikelet closed x 

 Df the slender subterranean branches. (Dfilium Amphi- Same wide open x2. 

 tarpon Pursh ; A. Amphicarpon Nash.) Moist sandy Basal fertile sptkelet, 

 pine barrens, N. J. to Fla. Sept. FIG. 66. partly open x2. 



9. PASPALUM L. 



Spikelets 1-flowered, plano-convex, nearly sessile, solitary or in pairs, in 2 

 rows on one side of a continuous narrow or dilated rhachis, forming simple spike- 

 like racemes ; spikelets placed with the back of the fertile lemma toward the 

 rhachis ; first glume obsolete (rarely present) ; lemma and palea chartaceous- 

 indurated, margins of the lemma inrolled. Perennials, with 1-several racemes 

 digitate or racemose at the summit of the culm and branches. (ncunrdXos, a 

 Greek name for millet.) 



a. Racemes 1-several, 1 terminal and often 1 or more lateral ft. 

 b. Rhachis inembranaceous, 2 mm. or more broad. 



Spikelets 1.5 mm. long, elliptical, pubescent . . . 1. P. mucronatum. 



Spikelets 2 mm. long, oval, glabrous 2. P, dissectum. 



b. Rhachis narrow, not membranaceous, less than 1 mm. broad 



(except in P. Eoscianum) c. 

 c. Axillary peduncles 1 or more from uppermost sheath ; leaves 



ciliate on the margin d. 

 d. Spikelets 2 mm. long e. 



e. Leaves glabrous on both surfaces . . . . 5. P. ciUatifolivm. 



e. Leaves pubescent on one or both surfaces /. 

 f. Spikelets glabrous. 



Leaves densely long-pubescent. 



Culm hirsute below raceme 6. P. pube,*ctn*. 



Culm glabrous 7. P. Muhlenbergii. 



Leaves puberulent and sometimes sparsely villous . 8. P. utraminevm. 

 f. Spikelets pubescent ; leaves short-pubescent. 



Culms erect 9. P. Buhii. 



Culms prostrate . 10. P. psammopMlnm. 



d. Spikelets 1.5 mm. long. 



Spikelets glabrous 8. P. longipedunculatvm. 



Spikelets pubescent 4. P. setaceum. 



C. Axillary peduncles none g. 

 g. Spikelets glabrous h. 



h. Spikelets singly disposed so as to appear in 1-2 rows. 

 Spikelets 2.5 mm. long. 



Plants glabrous or sparingly pilose. 

 Leaf-blades of culm 1-2 dm. long ; racemes 8-6 



cm. long 11. P. laene. 



Leaf-blades of culm 2-4 dm. long; racemes 8-10 



cm. long 12. P. angustifolivm 



Plants with pubescent sheaths and blades . . .18. P. plenipilum. 

 Spikelets 3 mm. long; sheaths papillose-hirsute . . 14. P. circulare. 

 Spikelets 4 mm. long. 

 Leaf-blades less than 1.5 dm. long .... 16. P. difforme. 



Leaf-blades 2-t dm. long 15. P. Jtoridanum. 



h. Spikelets in pairs so as to appear In four rows. 



Spikelets stramineous at maturity . . . . . 17. P. laeviglumf. 



Spikelets dark brown at maturity 18. P. JBoncianum. 



g. Spikelets ciliate 19. P. dilatatum. 



a. Racemes a pair at the summit of the culm . . . . . 20. P. dittichum. 



* Racemes with a broad, thin-membranaceous, or foliaceous and keeled, rhachis, 

 2 mm. wide or more, the incurved margins partly inclosing the small 2-rowed 

 spikelets. (Aquatic or nearly so, decumbent or floating.) 



1. P. mucronatum Mulil. Sheaths papillose-hirsute or nearly smooth, in- 

 flated ; blades lanceolate, 2.5-15 cm. long, 6-14 mm. wide, scabrous; raceme* 

 10-50, finally spreading ; rhachis extending beyond the spikelets, which are ellip- 

 GHAT'S MANUAL 7 



