Part 7 - UNC Herbarium

POACEAE 924
Tridens Roemer & J.A. Schultes (Triodia, Redtop, Tridens, Fluffgrass)
A genus of about 14 species, native to the Western Hemisphere. References: Valdés-Reyna in FNA (2003a).
1 Panicle dense and spike-like, > 4× as long as wide, the branches ascending to appressed.
2 Plants from elongate rhizomes; lemma 4-5 mm long; spikelet 7-9 mm long ............................................. T. carolinianus
2 Plants cespitose; lemma 2.5-3 mm long; spikelet 4-6 mm long .......................................................................... T. strictus
1 Panicle open and spreading, < 4× as long as wide, the branches well-developed and spreading-ascending to reflexed.
3 Spikelets 4-5 mm long, 2.5-3.5 mm wide .......................................................................................................T. ambiguus
3 Spikelets 6-8 mm long, 1.5-2.2 mm wide.
4 Primary pulvini densely pubescent, the hairs encircling the base of the panicle branch; secondary pulvini
pubescent; spikelets mostly on pedicels 3-20 mm long; main branches of the inflorescence stiffly spreading...........
...............................................................................................................................................................T. chapmanii
4 Primary pulvini glabrous to sparsely pubescent, tufted only in the axil (the upper surface of the panicle branch);
secondary pulvini glabrous; spikelets on pedicels mostly < 3 mm long; main branches of the inflorescence
spreading, ascending or drooping.................................................................................................................. T. flavus
Tridens ambiguus (Elliott) J.A. Schultes, Pineland Triodia, Flatwoods Fluffgrass. Cp (GA, NC, SC): wet savannas, claybased
Carolina bays; uncommon (rare north of GA) (NC Rare). August-October. S. NC south to FL, west to e. TX. [= RAB,
FNA, GW, HC, K; = Triodia elliottii Bush – S]
Tridens carolinianus (Steudel) Henrard, Carolina Triodia, Carolina Fluffgrass. Cp (GA, NC, SC): mesic swales in
sandhills; rare (GA Rare, NC Rare). August-October. S. NC south to FL, west to LA. [= RAB, FNA, HC, K; = Triodia
drummondii Scribner & Kearney – S]
Tridens chapmanii (Small) Chase, Chapman's Triodia. Cp (GA, NC, SC, VA): loamy sands of disturbed longleaf pine
woodlands, roadsides; rare (NC Watch List). August-October. NJ south to FL, west to TX and OK. [= HC; = Tridens flavus
(Linnaeus) A.S. Hitchcock var. chapmanii (Small) Shinners – RAB, C, FNA, K; = Triodia chapmanii (Small) Bush – F, G; <
Triodia flava (Linnaeus) Smyth – S]
Tridens flavus (Linnaeus) A.S. Hitchcock, Redtop, Tall Redtop, Purpletop Tridens, Greasy Grass. Cp, Pd, Mt (GA, NC,
SC, VA): roadsides, disturbed areas, glades; common. July-October. NH west to NE, south to FL and TX. [= HC; = Tridens
flavus var. flavus – RAB, C, FNA, K; = Triodia flava (Linnaeus) Smyth – F, G; < Triodia flava (Linnaeus) Smyth – S (also see
Tridens chapmanii); < Tridens flavus – W]
Tridens strictus (Nuttall) Nash, Spike Triodia, Longspike Fluffgrass, Longspike Tridens. Cp (GA, NC, SC, VA), Pd (GA,
SC, VA): sandhills, moist pine savannas, roadsides; rare (NC Rare, VA Rare). August-October. S. VA south to AL, west to TX,
north in the interior to IL and KS. It is possible that this grass is introduced only north and east of GA (thus in our entire area).
Rhoads & Klein (1993) report an old specimen from w. PA. [= RAB, FNA, GW, HC, K; = Triodia stricta (Nuttall) Bentham ex
Vasey – F, G, S]
Triplasis Palisot de Beauvois (Sandgrass)
A genus of 2 species, of eastern and central North America south through Mexico to Costa Rica. References: Hatch in FNA
(2003a).
Identification notes: The foliage of both of our species has a sour taste.
1 Lemma awn 4.5-8 mm long; culm internodes appressed pilose or puberulent; perennial......................................T. americana
1 Lemma awn 0.5-1.5 mm long; culm internodes glabrous to minutely scaberulous; annual (or rarely perennial) .......................
......................................................................................................................................................... T. purpurea var. purpurea
Triplasis americana Palisot de Beauvois, Southern Sandgrass. Cp (GA, NC, SC): open sandy areas; common. August-
October. A Southeastern Coastal Plain endemic: NC south to FL, west to e. LA. [= RAB, FNA, HC, K, S]
Triplasis purpurea (Walter) Chapman var. purpurea, Purple Sandgrass. Cp (GA, NC, SC, VA): dunes, maritime dry
grasslands, open sandy areas; common. September-October. NH south to FL, and west to TX, along the coast; also around the
Great Lakes, and in central United States. Var. caribensis R.W. Pohl is in the New World tropics. [= FNA; < T. purpurea –
RAB, C, F, G, HC, K; > T. intermedia Nash – S; > T. purpurea – S]
Tripsacum Linnaeus (Gamma Grass)
A genus of about 12 species, tropical and subtropical American. References: Barkworth in FNA (2003a); DeWet, Harlan, &
Brink (1982)=Z.