Usually perennial grasses, with flat or involute leaf-blades, and the inflorescence composed of open or contracted and sometimes spike-like panicles. Spikelets 3-many-flowered, the flowers perfect or the upper ones staminate. Scales 5-many, membranous, sometimes firmer, the 2 lower empty, keeled, obtuse to acuminate, usually shorter than the rest, sometimes longer; flowering scales 3-nerved, the midnerve or all the nerves excurrent, the mid-nerve and the lateral nerves or the margins pilose, the apex entire or shortly 2-toothed, the teeth obtuse to acute, the callus short and obtuse; palet shorter than the scale, compressed, 2-keeled. Stamens 3. Styles short, distinct. Stigmas plumose. [Latin, in reference to the teeth of the flowering scales.]

Species about 30, natives chiefly of temperate regions. Type species: Poa coerulescens Michx.

1. Tridens Flava (L.) Hitchc. Tall Red-Top

Fig. 561

Poa flava L. Sp. PI. 68. 1753.

Poa seslerioides Michx. Fl. Bor. Am. 1: 68. 1803. Tricuspis seslerioides Torr. Fl. N. Y. 2: 463. 1843. Sieglingia seslerioides Scribn. Mem. Torr. Club 5: 48. 1894. Tridens flava Hitchc. Rhodora, 8: 210. 1906.

Culms 2°-5° tall, erect, often viscid above. Sheaths sometimes villous at the summit, equalling or shorter than the internodes; ligule a ring of very short hairs; blades 4'-1° long or more, 3"-6" wide, flat, attenuate into a long tip, smooth beneath, scabrous above; panicle 6'-18' long, the branches finally ascending or spreading, the lower 4'-10' long, usually dividing above the middle; spikelets 4-8-flowered, 3"-4" long, purple; joints of the rachilla short; empty scales glabrous, obtuse, generally slightly 2-toothed; flowering scales oval, the nerves pilose, ex-current as short points.

In fields, Massachusetts and New York to Kansas, south to Florida and Texas. July-Sept.

2. Tridens Stricta (Nutt.) Nash. Narrow Three-Toothed Grass

Fig. 562

Windsoria stricta Nutt. Trans. Am. Phil. Soc. (II.) 5:

147. 1833-37. Tricuspis stricta A. Gray, Proc. Phila. Acad. 1862: 335.

1863. Sieglingia stricta Kuntze, Rev. Gen. PI. 789. 1891. Tridens stricta Nash, in Small, Fl. SE. U. S. 143. 1903.

Culms 1 1/2°-4° tall, erect. Sheaths shorter than the internodes; ligule a ring of short hairs; blades 6'-1° long or more, flat, long-acuminate, smooth beneath, scabrous above; spike-like panicle 5'-12' in length, the branches appressed, the lower 1'-2' long; spike-lets 4-10-flowered, 2"-3" long, the joints of the rachilla very short; lower scales usually about two-thirds as long as the spikelet, rarely extending beyond the flowering scales, acute, glabrous; flowering scales ovate, the nerves pilose for more than half their length, the middle and often the lateral excur-rent as short points.

Moist soil, Missouri and Kansas to Mississippi and Texas. July-Oct.

3. Tridens Elongata (Buckley) Nash. Long-Panicled Three-Toothed Grass

Fig. 563

Uralepis elongata Buckley, Proc. Phila. Acad. Sci.

1862: 89. 1863. Sieglingia elongata Nash, in Britt. & Br. 111. Fl. 3:

504. 1898. Tricuspis elongata Nash, Britt. Man. 127. 1901. Tridens elongata Nash, in Small, PI. SE. U. S. 143.

1903.

Culms 1°-3° tall, tufted, erect, rough. Sheaths rough, longer than the internodes, a ring of hairs at the apex, the lower sheaths usually sparingly papillose-pilose; blades rough, usually involute when dry, 3'-10' long, 1"-2" wide; panicle narrow, 5'-10' long, 1/2 wide, its branches erect, 1 1/2' or less long; spikelets 10-12-flowered, 4 1/2"-6" long, the empty scales scabrous, hispidulous on the midnerve, the first 1-nerved, the second 3-nerved; flowering scales about 3" long, obtuse at the scabrous apex, 3-nerved, the lateral nerves vanishing at or below the apex, the midnerve usually excurrent in a short point, all the nerves pilose below the middle.

Prairies, Missouri to Colorado, Arizona and Texas. June-Aug.