142 POACEAE 
B. Panicle narrow, often spike-like, its branches erect or appressed. 
Second empty scale I-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. 7. Drummond. 
Sheaths glabrous: spikelets erowded, the empty scales narrow and 
often equalling or exceeding the flowering scales. 7. T. strictus. 
Panicle less than 1 dm. long: spikelets turgid, the palet-nerves abruptly 
and strongly gibbous at the base. : 
Lateral nerves of the flowering scale vanishing below the apex : nerve-hairs 
about 1.5 mm. long. 9. T. muticus. 
Second empty scale 3-5-nerved. 
Spikelets 8-10-flowered, 10-14 mm. long, the hairs on the margins and mid- 
8. T. congestus. 
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. 
1l. 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 l-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. — [ T’riodia eragrostoides Vasey & Scribn.] 
On hillsides, southern Florida and Texas. Alsoin Mexico. Summer and fall. 
2. Tridens Texànus (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 em. long, its branches at length spreading, the lower 
2-7 em. long: spikelets loosely disposed, 8-11-flowered, 8-10 mm. long, oblong to narrowly 
ovate; empty scales rather broad, I-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 Tecana '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 mm. wide: panicle loose and open, 8-20 em. 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 ambigua ( EM.) Vasey.] 
In dry pine lands, South Carolina to Florida. Summer and fall, 
4. Tridens Langloisii Nash. Stems 5-15 dm. tall, smooth : 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 em. long, the axils more or less villous: spikelets usually 
numerous, 5-8-flowered, 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. [Z'riodia cuprea Jacq. | 
In dry soil, New York to Illinois, Kansas, Florida and Texas. Summer and fall.— 7. seslerioides 
Chapmánii (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. RED-TOP. 
