Herbs, perennial, rhizomatous, 0.5--5 dm. Rhizomes 2--4 mm diam., not swollen. Culms erect, terete, 1--3 mm diam., smooth. Cataphylls 0--1, straw-colored or maroon, apex acute. Leaves: basal 0--2, cauline 1--2(--5); auricles 0.5--1.2 mm, apex rounded, scarious; blade green to straw-colored, terete, 1.5--12 cm ?x 0.5--1.1 mm. Inflorescences terminal panicles of 5--25 heads, 3--11 cm, branches erect to ascending; primary bract erect; heads 2--10-flowered, obpyramidal, usually with some flowers short-pedicellateled, 2--6 mm in diam. Flowers: tepals greenish to straw-colored, lanceolate to oblong; outer tepals 1.8--3 mm, apex obtuse, mucronate; inner tepals 1.6--2.7 mm, apex obtuse; stamens 6, anthers 1/2 filament length. Capsules equaling perianth to usually exserted, chestnut brown to straw-colored, imperfectly 3-locular, oblong to oblong-ovoid, 2.3--3.5 mm, apex obtuse, valves separating at dehiscence. Seeds oblong to ovoid, 0.5--0.7 mm, not tailed. 2n = 40.
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Much like no. 38 [Juncus articulatus L.], avg a little smaller, mostly 0.5–3 dm; infl slender, 5–15 cm, less than half as wide, its branches ± closely ascending or erect; tep mostly 1.5–2.5 mm, the sep obtuse or rounded but sometimes minutely apiculate, the pet a little shorter, generally broadly rounded at the tip; fr obtuse or rounded to the stylar apiculation; 2n=40, 80. Wet meadows and sandy or gravelly shores; circumboreal, s. in our range to Pa., Ind., and Mo. (J. alpinus) The name J. alpinoarticulatus ssp. americanus (Farw.) Hämet-Ahti has been proposed to cover most of the American plants, together with those from Kamchatka and easternmost Siberia, but the taxonomy and nomenclature are complex. The hybrid with no. 38 is J. ×alpiniformis Fernald; that with no. 30. is J. ×stuckeyi M. Reinking.
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