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.
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.
Juncus tenuis is a cosmopolitan rush species that has a broad, almost worldwide presence; for example, in North America it occurs in all fifty states of the USA and all Canadian provinces save for Nunavit and Yukon. Also known by the common name of Path rush, it is present along many man-made as well as animal runway paths, since the sticky seeds are often dispersed by clinging to mammals.
This perennial herb grows in tufts that reach up to 40 centimeters in height. Flowers present in the form of terminal panicles. The flowering season is typically June and July.
In general Path rush appears to prefer disturbed habitats, which may explain its broad distribution; Besides path verges, it is found in open woodlands, gravelly seeps, pastures, abandoned fields and other barren waste areas. It is also tolerant of a wide range of soil types, and is much more adapted to compacted soils than most plants.
The Path Rush is one of the more common Juncus spp., but it is rather small in size and inconspicuous. Many different forms of the Path Rush have been described that freely intergrade. Other similar rushes include Juncus interior (Inland Rush) and Juncus dudleyi (Dudley's Rush), although these latter two species are usually larger in size. These rushes can be distinguished by examining the apex of their basal sheaths. The Path Rush has an auriculate sheath with a pair of lanceolate extensions that are membranous and fragile. The sheath of the Inland Rush has a pair of short auricles that are soft and rounded, while the sheath of Dudley's Rush has a pair of short auricles that are hard (cartilaginous) and rounded.