keys to the vascular plants of east texas - Botanical Research ...

1082 POACEAE/TRIDENS
REFERENCES: Tateoka 1961; McKenzie et al. 1987b; Peterson et al. 1997; Valdés-Reyna 2003a.
1. Panicle contracted, densely-flowered or elongate and spike-like, the panicle branches usually
with spikelets nearly to base or apparently so (branches usually tightly appressed at base).
2. Glumes much longer than the lower lemmas, usually extending to tip of distal florets or beyond
(i.e., glumes usually as long as or longer than rest of spikelet); plants 50–170 cm tall
______________________________________________________________________________ T. strictus
2. Glumes slightly longer than to shorter than lower lemmas, not extending to tip of distal florets
(i.e., much shorter than rest of spikelet); plants 20–80(–100) cm tall.
3. Lemmas glabrous or hairy only at extreme base, awnless ____________________________ T. albescens
3. Lemma veins ciliate or puberulent to well above the base (at least lower third of lemma
with hairs), awnless or awned.
4. Lemmas awnless, the veins usually with pubescence to well beyond middle; panicle 6–
20(–25) cm long, 10 mm or less wide ____________________________________________ T. muticus
4. Lemmas short-awned, the midvein excurrent (= extending slightly beyond margin), the
veins with pubescence only on lower 1/3–1/2; panicle 5–8(–10) cm long, 12–25 mm
wide ___________________________________________________________________ T. congestus
1. Panicle open, � loosely-flowered, neither densely-flowered nor spike-like, the panicle branches
conspicuously bare of spikelets at base.
5. Lateral spikelets (= those not terminating an inflorescence branch) with pedicels ca. 1 mm or
less long; inflorescence branches stiffly ascending; species of Pineywoods and Gulf Prairies
and Marshes _________________________________________________________________ T. ambiguus
5. Lateral spikelets (at least some) with pedicels � 1 mm long; inflorescence branches (at least
some) spreading and/or flexuous; including species widespread in East TX.
6. Lemmas 2–3.2 mm long; species known in East TX only from Bexar and Hays cos. near
extreme sw margin of area _________________________________________________ T. eragrostoides
6. Lemmas 4–6 mm long; including species widespread in East TX.
7. Lemmas with lateral veins usually not reaching the lemma margin (use hand lens or
dissecting scope); spikelets with 3–5 florets; species known in East TX only from Bexar,
Comal, Hays, and Travis cos. on extreme sw margin of area _______________________ T. buckleyanus
7. Lemmas with lateral veins reaching the lemma margin and often extending slightly
beyond it (= excurrent) as short points (= mucros); spikelets with 4–12 florets; including
species widespread in East TX.
8. Leaf blades (3–)5–10(–13) mm wide; panicle mostly 15–35(–40) cm long; plants 60–
180 cm tall; spikelets 5–9(–10) mm long, with 4–8 florets; species widespread in East
TX _______________________________________________________________________ T. flavus
8. Leaf blades mostly 1–3(–5) mm wide; panicle mostly 5–16 cm long; plants 20–75 cm
tall; spikelets usually 6–13 mm long, with 6–12 florets; species known in East TX mainly
from sw margin of area ____________________________________________________ T. texanus
Tridens albescens (Vasey) Wooton & Standl., (whitish), WHITE TRIDENS, WHITETOP, WHITE FLUFF
GRASS. Plant 30–60(–100) cm tall, glabrous; leaf blades 1–4 mm wide; panicle 6–30 cm long;
spikelets 4–10 mm long; lemmas white, often purplish distally, the spikelets thus often appearing
banded. Low prairies, ditches, swales, and other periodically wet areas, often in clay soils;
nearly throughout TX except the Pineywoods; sc U.S. from KS s to TX w to AZ. Mar–Nov.
[Rhombolytrum albescens (Vasey) Nash, Triodia albescens Vasey]
Tridens ambiguus (Elliott) Schult., (uncertain, doubtful), PINE-BARREN TRIDENS, PINE-BARREN
FLUFF GRASS. Plant 60–125 cm tall, nearly glabrous; leaf blades usually 2–5 mm wide; panicle 8–
20 cm long; spikelets 4–6 mm long. Wet pinelands and adjacent areas; Hardin, Red River, Tyler
(BRIT), Liberty (SBSC), Angelina, Jasper, and Newton (Turner et al. 2003) cos. in the
Pineywoods; se U.S. from NC s to FL w to TX. Sep–Nov. [Poa ambigua Elliott, Triodia ambigua
(Elliott) Benth. ex Vasey, Triodia elliottii Bush]