[++] Stamens 6.
19. J. articulàtus, L. Stems ascending or erect (9–15´ high), tufted from a short creeping rootstock, with 1 or 2 slender leaves; panicle short, spreading, the crowded heads 3–8-flowered; flowers brown, rarely pale (1¼–1½´´ long); sepals lance-oblong, acute or mucronate, or the 3 inner obtuse and a little longer, shorter than the ovate-oblong acute or abruptly mucronate-pointed incompletely 3-celled commonly deep chestnut-brown shining capsule; anthers as long as the filaments; ovary attenuate into a short style; seeds (less than {1/3}´´ long) obovate, attenuate below, abruptly pointed above.—Wet grounds, Newf. to Del., west to western N. Y. and Mich. (Eu.)
20. J. alpìnus, Villars, var. insígnis, Fries. Stems erect (9–18´ high) from a creeping rootstock, with 1 or 2 slender leaves; panicle meagre, with erect branches bearing distant greenish or light-brown heads, each of 3–6 flowers (1¼–1½´´ long); sepals oblong, obtuse, the outer mucronate or cuspidate and usually longer than the rounded inner ones, as long as or shorter than the obtuse short-pointed incompletely 3-celled light-brown capsule; anthers as long as the filaments; style short; seeds ({1/3}´´ or more in length) spindle-shaped.—Wet sandy banks, L. Champlain, Cayuga Lake, along the Great Lakes, and far west and northward. (Eu.)
21. J. militàris, Bigel. Stem stout (2–4° high) from a thick creeping rootstock, bearing a solitary stout erect leaf (½–3½° long) below the middle, which overtops the crowded and rather contracted panicle; heads numerous, 5–12- (rarely 25-) flowered; flowers brownish (1½´´ long); sepals lanceolate, the outer awl-pointed, as long as the ovate-oblong triangular taper-beaked 1-celled capsule; anthers longer than the filaments; ovary attenuate into a slender style; seeds (¼–{1/3}´´ long) globose-obovate, obtuse, abruptly pointed.—In bogs and streams, Maine to Md. Sometimes producing, in flowing water, numberless capillary submersed leaves, 2–3° long, from the rootstock.
[++][++] Stamens 3.
22. J. acuminàtus, Michx. Stems tufted, erect, slender (1–2° long), bearing about 2 leaves and a very loose spreading panicle; heads rather few and large, 5–many-flowered, greenish, at length straw-colored or darker; sepals lance-awl-shaped, sharp-pointed, equal (1½–2´´ long), as long as the triangular-prismatic short-pointed 1-celled straw-colored or light brown capsule; anthers a little shorter than the filaments; style almost none; seeds small ({1/5}–{1/4}´´ long), acute at both ends, ribbed-reticulated.—N. Eng. to Ga., Minn. and Tex. May, June. Very variable. Heads often proliferous in autumn.
Var. débilis, Engelm. Stems slender (9–18´ high); heads green, 3–6-flowered, in a loose panicle; flowers smaller (1¼–1½´´ long); capsule longer than the sepals.—Wet sandy soil, N. J. to S. C., west to Ohio, Mo., and Miss. Stem sometimes decumbent and rooting.
Var. robústus, Engelm. Stems stout, tall (2–4° high), bearing numerous 5–8-flowered light-brown heads in a large much-branched panicle; flowers small (1–1{1/5}´´ long); ovoid capsule scarcely longer than the sepals.—Deep swamps, Ill. to Mo. and La.
[+][+][+] Heads few, crowded, of numerous flowers.
[++] Stamens 3; stem rigid from a thick white horizontal rootstock.