Juncus arcticus balticus
Rush family (Juncaceae)
This perennial rush is 1-3' tall and unbranched. The central stem is
1-3 mm. across, medium green, glabrous, and terete. Basal leaves at the
base of the stem have been reduced to sheaths. These sheaths are ½–6"
long, glabrous, and reddish or brown; they are often partially buried
by sand or soil. The central stem terminates in a panicle of solitary
spikelets and a spathe that looks like a continuation of the stem. This
spathe is 2-16" long, 1-2 mm. across, medium green, glabrous, and
terete. The panicle of spikelets has ascending branchlets (or rays)
that are ¼–6"
long; they are filiform and often slightly curved or sinuous. These
branchlets usually subdivide into secondary branchlets that have one to
several solitary spikelets on short filiform pedicels. There are 5-50
spikelets per panicle. Individual spikelets are 3-5 mm. long,
consisting of 3 chaffy petals, 3 chaffy sepals, 6 stamens, and a pistil
with a style that divides into 3 sinuous stigmas.
The petals and sepals
are about the same length and lanceolate in shape; they are
green-veined in the middle (later becoming brown), while their margins
are membranous. The elongated anthers are pale yellow; they are about
twice as long as their filaments. Underneath the spikelets, there are
usually a few chaffy scales that are lanceolate to ovate in shape. The
blooming period occurs from late spring to early summer, lasting about
1-2 weeks. The flowers of the spikelets are cross-pollinated by the
wind. Afterwards, these flowers are replaced by seed capsules that are
about the same length or slightly longer than the sepals and petals;
these capsules are lanceoloid in shape and become brown at maturity.
The capsules divide into 3 parts to release their tiny seeds later
during the summer. Mature seeds are 0.5–1 mm. in length, brown,
ellipsoid and somewhat compressed in shape; they are small and light
enough to be blown about by the wind. The shallow root system is
long-rhizomatous and fibrous. Colonies of clonal plants often develop
from the rhizomes. Sometimes these clonal plants form lines along the
Cultivation: The preference is full sun, wet to
conditions (including shallow water), and sandy soil. Plants can be
propagated by division of the long rhizomes. Dry
conditions and shade are poorly tolerated. However, this plant is very
Range & Habitat:
The native Baltic Rush is
largely restricted to NE Illinois, where it is uncommon (see Distribution Map).
Outside of the
state, this rush has a large range that extends from the Atlantic coast
(including New England & Canada) to the Pacific coast. Some
varieties or subspecies of this rush also occur in Europe and Mexico.
In Illinois, habitats include sandy pannes along Lake Michigan, borders
of sandy ponds, interdunal swales along Lake Michigan, sand bars and
gravel bars along rivers, and sandy ditches along railroads. In
Illinois, the Baltic Rush is usually found in high quality natural
areas. Outside of the state, this rush also occurs in brackish marshes
and alkaline wetlands.
Faunal Associations: Insects that feed on
Baltic Rush (Juncus arcticus balticus) and other
rushes (Juncus spp.)
include such species as Spharagemon collare
(Mottled Sand Grasshopper),
the aquatic leaf beetle Plateumaris pusilla,
stem-boring larvae of some
Cerodontha spp. (Agromyzid flies), the seed bugs Cymodema
breviceps and Cymus angustatus, the
aphids Rhopalosiphum nymphaeae
and Prociphilus corrugatans, and Livia
maculipennis (Rush Psyllid). The
larvae of such moths as Archanara subflava (Yellow
Sedge Borer), Bactra
verutana (Javelin Moth), and Chilo forbesellus
(Crambid moth sp.) also
feed on rushes (see Brust et al., 2008; Clark et al., 2004; Spencer
& Steyskal, 1986; Hoffman, 1996; Blackman & Eastop,
1917; Harms & Grodowitz, 2009; Miller, 1987). Some vertebrate
animals feed on Baltic Rush and other rushes. The seed capsules
are eaten by such waterfowl as the Green-winged Teal, Blue-winged Teal,
Mallard, Northern Pintail, Gadwall, American Wigeon, Northern Shoveler,
Redhead, Ruddy Duck, American Coot, and Canada Goose (Hauser, 2005).
Muskrats feed on the rhizomes and bases of these plants, while hoofed
mammalian herbivores eat the coarse foliage sparingly. Dense
stands of Baltic Rush and similar plants provide nesting habitat for
ducks and other wetland birds; the Yellow Rail uses the stems of Baltic
Rush in the construction of its nests. Dense stands of Baltic Rush and
similar plants provide protective cover in wetlands for small birds and
of wildlife. (Hauser, 2005).
Photographic Location: Near a sandy pond along
Lake Michigan at Illinois Beach State Park in NE Illinois.
Among rushes (Juncus spp.),
Baltic Rush is fairly
easy to identify
because its panicle of spikelets appears to be produced laterally near
the middle of its stem. In reality, this inflorescence is produced from
the apex of
the stem, while a stem-like spathe rises above it. The only other rush
with this characteristic is Soft Rush (Juncus effusus).
rush can be distinguished from Baltic Rush by its densely clustered
stems, which have a rosette-like appearance. In addition, the spikelets
of Soft Rush are less elongated in shape than those of Baltic Rush. The
Baltic Rush has an unstable taxonomic history that continues to the
present time. For example, the ITIS refers to this rush as Juncus
balticus littoralis, the USDA refers to this rush as Juncus
littoralis, and eFloras refers to this rush as Juncus
balticus. The last scientific name has been adopted here.
varieties or subspecies of this rush exist, but they do not occur in
Illinois. Another common name of this species is Lake Shore Rush.