Thread Rush

Herbs, perennial, 0.2--3.5 dm. Rhizomes widely creeping, sparingly branched, 1.5--2 mm diam., nodes closely set. Culms terete, 1 mm diam. Cataphylls several. Leaves: blade absent. Inflorescences 3--10(--12)-flowered, loosely congested, 1--2 cm; primary bract terete, nearly equaling to much longer than culm. Flowers pedicellate; bracteoles broadly ovate, tepals light brown or green, lanceolate, 2.5--4.2 mm; inner series loosely subtending capsule at maturity, slightly shorter, margins scarious; stamens 6, filaments 0.5--0.9 mm, anthers 0.5--0.7 mm; style 0.2 mm. Capsules tan, 3-locular, nearly globose, 2.5--3  x 1.8--2.1 mm, shorter than perianth. Seeds amber, 0.5--0.6 mm, not tailed. 2n = 40, 70, 80, 84.

Plants perennial. Rhizome internodes short. Stems 7--15 cm × ca. 1 mm. Cataphylls usually 2, closely embracing stem, yellow, chestnut brown, or reddish brown, sheathlike, 1.5--5 cm; leaf blade reduced to an awnlike rudiment. Inflorescences pseudolateral, dense or lax, 3--6(--10)-flowered; involucral bract erect, seemingly a continuation of stem, terete, (0.3--)1--1.5 × as long as stem, apex sharply acute. Flowers pedicellate. Bracteoles 2, broadly ovate, apex obtuse. Perianth segments greenish, straw-colored with age, lanceolate, unequal to subequal; outer segments 2.6--5 × ca. 1 mm; inner segments ca. 2.5 × 1 mm. Stamens 6, ca. 2/3 as long as inner perianth segments; filaments ca. 1.1 mm; anthers oblong, 0.5--0.6 mm. Ovary obliquely ovoid, 3-loculed. Style very short or inconspicuous. Capsule yellowish green to pale brown, trigonous ovoid to trigonous globose, subequaling or longer than perianth, 3-septate, apex obtuse to acuminate, mucronate. Seeds pale chestnut brown, obliquely ovoid, ca. 0.5 mm. Fl. Aug, fr. Sep. 2 n = 84.

Greenland; St. Pierre and Miquelon; Alta., B.C., Man., Nfld. and Labr., N.B., N.S., N.W.T., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Colo., Idaho, Maine, Mass., Mich., Minn., Mont., Nebr., N.H., N.J., N.Y., Oreg., Pa., Utah, Vt., Wash., W.Va., Wis., Wyo.; Eurasia; Atlantic Islands (Iceland).

Heilongjiang, Jilin, Liaoning, Xinjiang [Japan; Europe, North America].

Flowering and fruiting summer.

Usually sandy, moist or wet soil along stream banks, pools, lakes or in meadow depressions, rarely in bogs, frequently hidden by larger vegetation; 0--3000m.

River valleys, near water; ca. 2500 m.

Juncus filiformis, called the thread rush, is a species of flowering plant in the genus Juncus, with a circumboreal distribution. It has been introduced to South Georgia Island. It is typically found in wetlands, on the borders of lakes and streams.