1 42 POACEAE 



B. Panicle narrow, often spike-like, its branches erect or appressed. 

 Second empty scale 1-nerved. 



Lateral nerves excurrent in short projections, the nerve-hairs less than 1 



mm. long. 

 Panicle exceeding 1.5 dm. in length : spikelets not turgid, the palet- 



nerves not gibbous at the base. 

 Sheaths, at least the basal, villous ; spikelets loosely arranged, the 



empty scales broad, % as long as the spikelet or less. 6. T. DrummondiL 



Sheaths glabrous : spikelets crowded, the empty scales narrow and 



often equalling or exceeding the flowering scales. 7. T. str ictus. 



Panicle less than 1 dm. long: spikelets turgid, the palet-nerves abruptly 



and strongly gibbous at the base. 8. T. congestus. 



Lateral nerves of the flowering scale vanishing below the apex : nerve-hairs 



about 1.5 mm. long. 9. T. muticits. 



Second empty scale 3-5-nerved. 



Spikelets 8-10- flowered, 10-14 mm. long, the hairs on the margins and mid- 

 nerve of the flowering scales copious. 10. T. elongatus. 

 Spikelets 3-5-flowered, 5-8 mm. long, the hairs on the margins and midnerve 



of the flowering scales scanty. 11. T. Buckleyanus. 



1. Tridens eragrostoides (Vasey & Scribn. ) Nash. Stems tufted, 3-12 dm. tall, 

 smooth : leaf-sheaths overlapping, rough ; blades erect or ascending, 2-3 dm. long, 4-7 

 mm. wide, long-acuminate, rough : panicle loose and open, 1.5-3 dm. long, its rough 

 branches ascending, the larger 3-12 cm. long: spikelets loosely arranged, 7-10-flowered, 

 4-5 mm. long, 2.5 mm. broad, ovate ; empty scales 1-nerved, acuminate, hispid on the 

 keel, the first much narrower than the second ; flowering scales about 2.5 mm. long, oval 

 and about 1.5 mm. wide when spread out, the apex rounded or nearly truncate, denticulate, 

 the hairs on their margins and midnerve about 0.2 mm. long, the midnerve usually excur- 

 rent, the lateral nerves vanishing at the- margin. [ Triodia eragrostoides Vasey & Scribn. ] 



On hillsides, southern Florida and Texas. Also in Mexico. Summer and fall. 



2. Tridens Texanus (Thurb. ) Nash. Stems tufted, 2-7 dm. tall, more or less hirsute 

 toward the base : stem-leaves 2 or 3 ; sheaths glabrous to sparingly hirsute, pilose at the 

 summit ; blades 3 dm. long or less, 2-4 mm. wide, long-acuminate, often more or less hir- 

 sute : panicle loose and open, 6-17 cm. long, its brandies at length spreading, the lower 

 2-7 cm. long : spikelets loosely disposed, 8-11 -flowered, 8-10 mm. long, oblong to narrowly 

 ovate; empty scales rather broad, 1-nerved, acute; flowering scales about 3.5 mm. long, 

 oval and about 2.5 mm. broad when spread out, the apex obtusely 2-toothed, their nerve- 

 hairs about 0.7 mm. long, the lateral nerves barely if at all excurrent, the midnerve shortly 

 so ; palet with the ciliolate nerves gibbous below the middle. [Triodia Texan* t Thurb.] 



On hills and in valleys, Louisiana to Arizona and northern Mexico. Summer. 



3. Tridens ambiguus (Ell. ) Schult. Stems 5-9 dm. tall, smooth : leaf-sheaths smooth 

 and glabrous; blades 0.5-3 dm. long, 1-3 rnm. wide : panicle loose and open, 8-20 cm. long, 

 its branches ascending, the larger 4-10 cm. long : spikelets loosely arranged, 7-9-flowered, 

 about 5 mm. long, 2.5-3 mm. wide, oval ; empty scales rather broad, acute, 1-nerved ; 

 flowering scales 3-3.5 mm. long, oval and about 2 mm. broad when spread out, their 

 nerve-hairs about 0.7 mm. long, the lateral nerves slightly excurrent, and the midnerve in 

 an awn about 0.3 mm. long ; palet ciliolate on the nerves, the internerve broadly ovate- 

 oval, the rounded apex decidedly apiculate. [ Triodia ambic/im ( Ell. ) Vasey. ] 



In dry pine lands, South Carolina to Florida. Summer and fall. 



4. Tridens Langloisii Nash. Stems 5-15 dm. tall, smo.oth : leaf-sheaths glabrous, or 

 pilose at the summit ; blades minutely pubescent above, the basal 2-4 dm. long, 2.5-5 mm. 

 wide, those on the stem shorter and narrower : panicle narrow, 1-2 dm. long, about 2 cm. 

 broad, its branches erect or nearly so, the larger 6-10 cm. long : spikelets loosely arranged, 

 4-6-flowered, 6-7 mm. long, 3-4 mm. wide ; empty scales rather broad, acute, 1-nerved or 

 the second rarely 3-nerved ; flowering scales about'4 mm. long, elliptic and 2.25 mm. wide 

 when spread out, their nerve- hairs about 0.5 mm. long, the apex minutely 2-toothed, the 

 nerves excurrent in short tips ; palet ciliate on the nerves, the apex obtuse, the inter- 

 nerve elliptic or elliptic-ovate. 



In pine lands, western Florida to Texas. Summer and fall. 



5. Tridens seslerioides (Michx. ) Nash. Stems tufted, 5-16 dm. tall, smooth : 

 stem-leaves 2-6 ; sheaths smooth, villous at the summit, those at the base crowded, the 

 remainder shorter than the internodes ; blades elongated, the basal and lower ones 2-6 dm. 

 long, 5-15 mm. wide, the uppermost one 6-20 cm. long, long-acuminate, smooth ; panicle 

 loose and open, 1.5-4 dm. long, its branches from nearly erect to spreading, drooping at 

 the end, the lower from 7-25 cm. long, the axils more or less villous : spikelets usually 

 numerous, 5-8-flo\Vered, 7-10 mm. long, elliptic to linear-oblong ; empty scales rather 

 broad, acute, 1-nerved ; flowering scales about 4 mm. long, their nerve-hairs about 0.7 mm. 

 long, the apex 2-toothed between the excurrent nerves. [Triodia cuprea Jacq. ] 



In dry soil, New York to Illinois. Kansas, Florida and Texas. Summer and fall. T. seslerioides 

 Chapmdnii( Small) Nash, differs from the species in its smaller panicle with more rigid branches and 

 more densely villous axils, and in the more acute teeth of the flowering scale. It occurs in Georgia, and 

 from Texas to Oklahoma and the Indian Territory. KKD-TOV. 



