Description: This native plant is a summer annual about
2-10" tall. Each plant produces a single culm or a tuft of culms. Each culm is
green, hairless, round in cross-section (terete), and unbranched. The leaves
are reduced to a single sheath at the base of the culm; there are no leaf
blades. This sheath is brown and rough-textured; there is often a single tooth
along its upper rim. The culm terminates in a small flowerhead up to ½"
long and a little less across. This flowerhead is ovoid in shape and consists
of many scales that are appressed together. These scales are whitish green to
brown, oval to ovate, and slightly convex along the outer surface; their
margins are often brown and papery. Behind each fertile scale, there is a
single flower with a bipartite style. The blooming period occurs during the
summer. Each flower produces a single achene about 1 mm. long and a little less
across. This achene is more or less brown, obovate in shape, and slightly
flattened along its length. At the apex of each achene, there is a flattened
tubercle with a short slender beak that corresponds to the base of the style.
This tubercle is nearly as broad as the achene. Each achene is usually
surrounded by several fine bristles that originate from the achene's base;
these bristles are about the same length as the achene (a 10x hand lens is
useful in observing these bristles and other characteristics of the achene).
The root system is fibrous. This plant spreads by reseeding itself and it often
forms colonies.
Cultivation: The
preference is full sun and wet conditions; shallow water is readily tolerated.
This plant can flourish in different kinds of soil, including those that are
sandy, gravelly, or mucky. It doesn't tolerate much competition from Typha
spp. (Cattails) and other tall wetland species.
Range & Habitat: Blunt Spike Rush is occasional
to locally common throughout most of Illinois; it is less common or absent in
the north central region. Habitats include marshes, fens, gravelly seeps,
interdunal flats, sedge meadows, low-lying areas along lakes and rivers,
drainage ditches, and poorly drained fields. In urban areas, Blunt Spike Rush
is occasionally found in disturbed grassy wetlands that are subjected to
occasional mowing from local landowners.
Faunal Associations: Various insects feed on the
foliage of Eleocharis spp. (Spike Rushes), including several
Limotettix spp. (Leafhoppers), the caterpillars of Cisseps
fulvicollis (Yellow-Collared Scape Moth), and the caterpillars of
Oarisma poweshiek (Poweshiek Skipperling). This latter species is
uncommon. The seedheads of Spike Rushes are eaten by dabbler ducks, rails, and
other wetland birds (see Wetland Bird Table for a listing of these species).
Canada Geese and Muskrats eat both the culms and seedheads. Dense stands of
Spike Rushes provide cover for frogs and abundant perching sites for
damselflies and dragonflies.
Photographic
Location: A grassy drainage ditch that was occasionally mowed over
by a local landowner in Champaign, Illinois. Usually, this practice destroys
most wetland species, but Blunt Spike Rush was able to thrive because of the
reduced competition from taller plants.
Comments: This is one of the shorter Eleocharis
spp. (Spike Rushes). To many people, Spike Rushes look like grass, but they
are actually sedges that consist of individual culms with a single scaly
flowerhead on top. As the common name suggests, the flowerhead of Blunt Spike
Rush is more blunt on top than those of many other Spike Rushes. Each of its
achenes has a tubercle that is unusually flat and broad and there are several
fine bristles surrounding the achene (usually about 6). Other Spike Rushes have
tubercles that are more narrow and conical, or their achenes lack bristles.
Mohlenbrock (1976/2001) describes 3 varieties of Blunt Spike Rush that occur in
Illinois; only var. obtusa is described here. The typical variety
(var. ovata) has a more conical tubercle on its achenes, while var.
detonsa has oblongoid flowerheads. Another scientific name for Blunt Spike
Rush is Eleocharis obtusa.