This perennial rush is 4-24" tall, often forming tufted plants.
The erect to ascending stems are mostly medium green (sometimes reddish
at their bases), glabrous, terete, and hollow. About 2-5 alternate
leaves occur along each stem; they are 1½-5" long and up to 1.5 mm.
across. The leaves are erect, ascending, or recurved; they are sheathed
at their bases. The leaf blades are mostly medium green, glabrous, and
linear-filiform in shape; they are terete to slightly flattened. The
leaf blade interiors are hollow with occasional crosswalls (septa).
Each stem terminates in an inflorescence consisting of an irregular
panicle of clustered flowers; this inflorescence is 1½-6" long and up
to one-half as much across, consisting of 3-30 clusters of flowers.
The branches of the inflorescence (or rays) are straight, stiff, and
variable in length; they are medium green, glabrous, and terete. Each
branch terminates in a cluster of 3-18 flowers spanning 5-15 mm.
across; at the base of each floral cluster, there are insignificant
chaffy bracts. Each flower consists of 6 tepals (3 outer and 3 inner
tepals) of about equal size and a 3-celled pistil with 3
stigmata. The stigmata are fuzzy white, while the anthers are pale
yellow. The persistent tepals are 2-3 mm. long and lanceolate to ovate
in shape with acute tips; they are greenish and sepaloid in appearance
while the flowers bloom, becoming reddish brown to dark brown shortly
The blooming period occurs during mid- to late summer for
about 2-3 weeks for a colony of plants. The flowers are
cross-pollinated by the wind. Shortly afterwards, the seed capsules
develop, becoming reddish brown to dark brown at maturity. The seed
capsules are 3-4 mm. long, ellipsoid, and 3-angled in shape; they have
short beaks at their apices that are relatively conspicuous.
Eventually, individual seed capsules divide into 3 parts, releasing
their tiny seeds. These seeds are up to 0.5 mm. in length, pale brown,
ellipsoid, and somewhat flattened in shape; their tips usually have
tiny appendages, but they are not winged. The tiny seeds can be carried
aloft by the wind or float to new areas on water. The root system is
fibrous and rhizomatous, occasionally forming clonal offsets.
The preference is full sun, wet to moist conditions, and calcareous
soil containing sand, clay, or a combination of the two. Occasional
inundation by shallow water is tolerated. This small
rush is not competitive with larger ground flora on fertile soil. It is
Range & Habitat:
The Jointed Rush has been found
in Cook County, Illinois, where it is rare (see Distribution
rush may be native to the state, or it could be adventive from outside
of the state. This rush is native to some areas of Eurasia, North
and North America. Habitats include margins of streams and
lakes, sandy ditches, sandy swales, sandy pannes, poorly drained areas
along railroads, and poorly drained areas of bicycle paths. This rush
often colonizes disturbed wetlands that are relatively open
Various insects feed on rushes (Juncus spp.
These species include the seed bugs Cymodema breviceps
, the leafhopper Macrosteles potoria
the root-feeding aphid Prociphilus
(Rush Psyllid), larvae of the
introduced sawfly Eutomostethus
, and stem-boring larvae of
two moths (Archanara
). The small
size, coarse foliage, and tiny seeds of this rush limit its usefulness
to vertebrate animals, although there is some evidence that the
rhizomes and crowns of wetland rushes are eaten by the muskrat,
while a dabbling duck, Anas
(Green-Winged Teal), feeds on their
seedheads. The tiny seeds of Jointed Rush may be transported to
new areas by the muddy feet and feathers of waterfowl, the muddy shoes
of humans, and the tire treads of bikes.
A poorly drained area of a bicycle path at the Indiana Dunes National
Lakeshore in NW Indiana, where there was a thin layer of sand above a
hard layer of gravel and clay.
This small rush to easy
to overlook and it is very similar in appearance to the Northern Green
). There is some evidence that the
Northern Green Rush is one of the parents of the polyploid Jointed Rush
These two species can be distinguished by the
shapes of their seed capsules: the seed capsule apices of Jointed Rush
are more tapered and pointed than those of Northern Green Rush. In
addition, the inner tepals of Jointed Rush have acute tips, while those
of Northern Green Rush usually have blunt tips. There is a tendency for
the inflorescence of Jointed Rush to be more divergent and less
elongated than the inflorescence of the latter rush, but there is some
overlap in the form of inflorescences between these two species.