Slender Rush

Juncus tenuis occurs throughout North America. It is particularly abundant in northeastern United States and eastern Canada, although infrequent in the south and west.

Through the use of isozyme electrophoresis, hybridization can be demonstrated between various members of the Juncus tenuis complex, including Juncus tenuis, J. anthelatus, J. interior, J. secundus, and J. dichotomus (R. E. Brooks, unpubl.). Juncus ××oronensis is thought to be a hybrid between J. tenuis and J. vaseyi in the northeast.

Herbs, perennial, tufted, 1.5--5 dm. Rhizomes densely branching. Culms few--20. Leaves basal, (1--)2--3; auricles 2--5 mm, apex acute, membranous; blade flat, 3--12 cm x 0.5--1 mm, margins entire. Inflorescences 5--40-flowered, borne congested or branch internodes ca. as long as tepals, ssomewhat loose, 1--5 cm; primary bract usually longer than inflorescence. Flowers: bracteoles 2; tepals greenish, lanceolate, 3.3--4.4 mm; outer and inner series nearly equal; stamens 6, filaments 0.5--0.9 mm, anthers 0.1--0.2 mm; style 0.1--0.2 mm. Capsules tan or light brown, 1-locular to pseudo-3-locular, ellipsoid, (3.3--)3.8--4.7 x (1.1--)1.3--1.7 mm, nearly equal to tepals. Seeds tan, ellipsoid to lunate, (0.52--)5.5--0.65(--0.7) mm, not tailed. 2n = 80.

Plants perennial, tufted. Stems 10--40 cm ( 0.6--1.2 mm, rigid to weak. Leaves basal; leaf sheath auricles obtuse, 2--4 mm, margin scarious to broadly so; leaf blade flat, 4--23 cm ( 0.5--1.8 mm, margin often involute. Inflorescences terminal panicles, 3--7 cm, usually lax, 6--40-flowered, rarely flowers in a few clusters; involucral bracts 2, leaflike, 4--18 cm. Bracteoles 2. Perianth segments greenish, lanceolate, 3.5--4 ( ca. 1 mm, subequal or outer ones somewhat longer than inner, margin white scarious, apex long tapered to a sharp point. Stamens 6; filaments ca. 1.2 mm; anthers ca. 0.8 mm. Style shorter than ovary; stigmas ca. 1.6 mm. Capsule trigonous ovoid, shorter than to rarely equaling perianth, apex truncate and shortly mucronate to obtuse. Seeds reddish brown, 0.4--0.5 mm, appendaged; appendage white, short. Fl. Jun--Jul, fr. Aug--Sep. 2 n = 30, 32, 84.

Heilongjiang, Henan, Jiangxi, Shandong, Taiwan, Zhejiang [India, Japan, Korea; Europe, North America].

Riversides, streamsides, wet grasslands; ca. 400 m.

Flowering spring--early summer. Exposed or shaded sites in soils ranging from sandy to clayey under moist or drier conditions, oftentimes these sites naturally or otherwise disturbed (e.g., game or human trails); Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; introduced worldwide.

Juncus bicornis Michaux; J. bicornis var. williamsii (Fernald) Victorin; J. macer Gray; J. macer forma williamsii (Fernald) F. J. Hermann; J. macer var. williamsii (Fernald) Fernald; J. tenuis var. bicornis (Michaux) E. Meyer; J. tenuis var. multicornis E. Meyer; J. tenuis var. williamsii Fernald

Juncus leptocladus Hayata; J. macer Gray.