12 POACEAE. 



Spikelets alternate ; spikes remote. 29. Leptochloa. 



ft Spikelets in open or spike-like panicles or racemes. 

 Rachilla with tiairs longer than the flowering 

 scales and enveloping them ; tall reed-like 

 grasses. 30. Phragmites. 



Rachilla and flowering scales glabrous. 



Flowering scales 3-nerved ; first 2 scales of 

 the spikelets empty. 

 Inflorescence of long branches, along which 

 the appressed spikelets are arranged on 

 short pedicels : lateral nerves of the 

 flowering scales pubescent. 31. Diplachne. 



Inflorescence an open or contracted pan- 

 icle, rarely racemose ; lateral nerves of 

 the flowering scale glabrous. 32. Eragrostis. 



Flowering scales 5-many-nerved ; first 2-6 

 scales of the spikelets empty. 

 Plants not dioecious ; spikelets flat, 2-edged. 33. Uniola. 

 Plants dioecious ; spikelets compressed. 34. Distichlis. 



2. Stems woody, perennial ; leaves on short branches which 



form dense whorls at the nodes. 35. ArthrosU/Udium. 



1. TRIPSACUM L. Sjst. Nat. ed. 10, 1261. 1759. 



Tall perennial grasses with thick rootstocks, rather broad, flat leaves and 

 monoecious flowers. Spikelets 1-2-flowered, in terminal or axillary, solitary or clus- 

 tered, elongated spikes. Staminate spikelets in 2 's at each node of the upper part 

 of the axis, 2-flowered, consisting of four scales, the two outer coriaceous, the two 

 inner thinner, the palet hyaline; stamens 3. Pistillate spikelets in excavations 

 at the lower joints of the spike, 1-flowered; stigmas exserted; style slender. 

 Grain partly enclosed in the excavations of the spikes, covered in front by the 

 horny exterior lower scale. [Name from the Greek, in allusion to the polished 

 outer scales.] About 7 species, natives of America, the following typical. 



1. Tripsacum dactyloides L. Syst. Nat. ed. 10, 1261. 1759. 



Rootstock 1.25-2.5 cm. thick; culms stout, erect, 1-2 m. tall. Leaves 

 smooth and glabrous, 3 dm. or more long, 1.25-3.75 cm. wide; spikes terminal, 

 and in the upper axils, solitary or 2-3 together, 1-1.25 dm. long; outer scales 

 of the staminate spikelets linear and obtuse, 8 mm. long, about 2 mm. wide, 

 faintly many-nerved; exterior scale of the pistillate spikelets horny, shining. 



Scrub-lands, Inagua : — Rhode Island to Nebraska, Florida and Texas ; Hispaniola ; 

 Trinidad ; Mexico ; South America. Gama-grass. 



2. IMPERATA Cirillo, PI. Ear. Neap. 2: 26. 1792. 



Perennial grasses with elongated leaves, the spikelets in dense terminal 

 spike-like, silvery-hairy panicles. Spikelets 1-flowered, rarely 2-flowered, un- 

 equally pedicellate in pairs; scales 4, thin, hyaline, awnless, the 2 outer ones 

 empty, pilose, the third glabrous, usually empty, the fourth glabrous, subtend- 

 ing a perfect flower and its 2-nerved palet. Stamens 1 or 2. Styles distinct, 

 stigmas plumose. [Commemorates Ferrante Imperate, Italian naturalist of the 

 sixteenth century.] About 5 species of tropical distribution. Type species: 

 Lagurus cylindricus L. 



1. Imperata brasiliensis Trin. Mem. Acad. St. Petersb. VI. 2: 331. 1832. 



Culms 8 dm. high, or less; sheaths glabrous; leaf-blades erect, 1-4 dm. 

 long, less than 1 cm. wide, the upper surface densely hirsute near the base, the 



