(Addendum) 13a. E. álbida, Torr. Like n. 12 and 13 in habit, somewhat stouter; spikelet dense, ellipsoidal or oblong, 1–4´´ long, acutish, with pale obtuse scales; achene very small, triangular-obovate, very smooth, with a broadly triangular tubercle upon a narrow base, shorter than or exceeding the reddish bristles.—Salt marshes, Northampton Co., Va. (Canby), and south to Fla. and Tex.
[+][+] Bristles 2–4, shorter than the achene, slender and fragile, or none.
14. E. ténuis, Schultes. Culms almost capillary, erect from running rootstocks, 4-angular and flattish (1° high), the sides concave; spikelet elliptical, acutish, 20–30-flowered (3´´ long); scales ovate, obtuse, chestnut-purple with a broad scarious margin and green keel; achene obovate, roughish-wrinkled, crowned with a small depressed tubercle, persistent after the fall of the scales; bristles ½ as long as the achene or none.—N. Scotia to N. C., Minn., and Mo. June.
15. E. compréssa, Sullivant. Culms flat, striate, tufted, erect (1–2° high); spikelet ovate-oblong, or at length lanceolate, 20–30-flowered (4–7´´ long); scales lanceolate-ovate, acute, dark purple with broad white pellucid margins and summit; achene yellowish, obovate-pear-shaped, obtusely triangular, wrinkled, crowned with a small conical and pointed tubercle; bristles 1–4, very slender, fragile, shorter than or equalling the achene (sometimes none or a single rudiment).—Wet places, N. Y. and Ont. to Minn. and Mo.
16. E. melanocárpa, Torr. Culms flattened, grooved, wiry, erect (9–18´ high); spikelet cylindrical-ovoid or oblong, thick, obtuse, densely many-flowered (3–6´´ long); scales closely many-ranked, roundish-ovate, very obtuse, brownish with broad scarious margins; achene smooth, obovate-top-shaped, obtusely triangular, the broad summit entirely covered like a lid by the flat depressed tubercle, which is raised in the centre into a short abrupt triangular point; bristles often obsolete; achene soon blackish.—Wet sand, Mass. to Fla.
17. E. tricostàta, Torr. Culms flattish (1–2° high); spikelet soon cylindrical, densely many-flowered (6–9´´ long), thickish; scales ovate, very obtuse, rusty brown, with broad scarious margins; achene obovate, with 3 prominent thickened angles, minutely rough-wrinkled, crowned with a short-conical acute tubercle; bristles none.—N. J. to Fla.
18. E. Wólfii, Gray. Culms slender (1° high), from very small creeping rhizomes, 2-edged; spikelet ovate-oblong, acute; scales ovate-oblong, obtuse, scarious, pale purple; achene pyriform, shining, with 9 nearly equidistant obtuse ribs and transverse wrinkles between them; tubercle depressed, truncate, more or less apiculate; bristles not seen.—Wet prairies, N. Iowa and S. Minn.
§ 4. Spikelet more or less flattened, thicker than the slender or capillary culm, few–many-flowered; the thin membranaceous scales somewhat 2–3-ranked; style 3-cleft; bristles of the perianth 3–6, fragile or fugacious. Small or delicate species, differing from the last division chiefly in the flattish spikelets.
[*] Tubercle contracted at its junction with the achene.
19. E. aciculàris, R. Br. Culms finely capillary (2–8´ long), more or less 4-angular; spikelet 3–9-flowered; scales ovate-oblong, rather obtuse (greenish with purple sides); achene obovate-oblong, with 3-ribbed angles and 2–3 times as many smaller intermediate ribs, also transversely striate, longer than the 3–4 very fugacious bristles; tubercle conical-triangular.—Muddy shores, across the continent. (Eu., Asia.)