1. Juncus L. (rush)
Plants sometimes with rhizomes and/or tubers, the aboveground growth caespitose
or spaced along the rhizome. Aerial stems usually erect or ascending, usually
unbranched below the inflorescence. Leaves glabrous, the leaf blades flat,
tubular, or folded longitudinally with boat-shaped tips, the basal leaves
usually few, sometimes reduced to bladeless sheaths, the leaves of the aerial
stems absent or few, the sheaths open. Inflorescences panicles or sometimes
reduced to racemes, usually with 1 or more leaflike or stemlike bracts at the
base, the individual flowers single, in small clusters, or in dense, headlike
clusters. Flowers in some species subtended by 2 small, triangular to ovate
bracts, in addition to the single bracts scattered through the inflorescence.
Sepals and petals similar to one another or sometimes the sepals slightly
longer, lanceolate to ovate, erect or with the acute to attenuate (rarely
obtuse) tips somewhat spreading, green or straw-colored to brown, usually
firm-textured with scarious margins. Stamens 3 or 6. Fruits shorter than or
longer than the perianth, obovoid to linear-attenuate, straw-colored to brown
(sometimes black or nearly so in J. gerardii). Seeds usually numerous,
0.3–2.0 mm long, ellipsoid to ovoid, yellow or brown, lacking a caruncle
(caplike appendage), but in some species with one or both ends tapered into
short or long, tail-like appendages, the surfaces variously pitted or
honeycombed. About 225 species, worldwide, but most diverse from temperate
regions to the Arctic.
The species of Juncus can be difficult to determine. Keying sterile or
flowering specimens is sometimes impossible, because in most species the mature
capsules provide characters critical to species determination. To correctly
identify a specimen, it is important to observe whether the individual flowers
are closely subtended by a pair of short bracts, as opposed to the scattered
small bracts in the inflorescences of other species groups.
The rushes are important components of many prairie and wetland communities.
Most of the species are good for erosion control in some situations, and
several species are effective colonizers of disturbed habitats. The seeds and
rootstocks provide food for diverse wildlife species, and the aboveground
portions are good forage for livestock and native grazing mammals.
Individuals of some species, particularly J. torreyi, produce aberrant
inflorescences in which most of the flowers in each cluster are replaced by
longer, green, leaflike structures. These gall-like growths are produced in
response to parasitism by small insects, particularly members of the Homopteran
genus of jumping plant lice, Livia Latreille.