BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juncus roemerianus | Black Rush 



GENERAL BOTANICAL CHARACTERISTICS : 
Black rush is a tufted, coarse and rigid, rhizomatous, perennial
grasslike herb.  It tolerates a wide range of environments, which
greatly affects its density and growth habit.  Where soil water salinity
is low, black rush is often very robust, with leaves reaching over 7
feet (2.1 m) in height, while in hypersaline areas the plants are
dwarfed, often less than 1 foot (0.3 m) tall [5].  Both tall and short
stature plants occur in most salt marshes, with the tallest plants
occurring near open water (low soil salinity) and the shortest near land
(high soil salinity because of longer and more frequent periods of
exposure) [25].  Conversely, plant density increases farther inland.  In
northwest Florida, stem density and height varied with elevation as
follows [25]:
                         
                         low marsh       upper marsh      high marsh
                        (deep water)                    (shallow water)

density (shoots/m2)        1660             2097             4719
live shoot density          885              993             1692   
dead shoot density          776             1164             3029

mean height (inches/cm)   40/102           35/88             31/78

Rhizomes average about 0.35 inch (9 mm) in diameter, and are primarily
located within 4 inches (10 cm) of the soil surface [5,28].  


RAUNKIAER LIFE FORM : 
   Geophyte
   Helophyte


REGENERATION PROCESSES : 
Black rush reproduces both sexually and asexually.  Existing stands are
maintained through vigorous rhizome growth, while new stands are
established via seed dispersal and seedling establishment.  Black rush
reproduction biology presented below is summarized from Eleuterius
[3,6].

Seed production and dispersal:  Two flowering types occur in black rush.
Plants produce either perfect flowers only, or pistillate flowers only.
Pistillate-flowered plants produce more and higher viability seeds than
perfect-flowered plants.  Seeds from a single inflorescence are shed
simultaneously.

Germination and seedling establishment:  Black rush seeds are highly
viable.  In Mississippi, germination averaged about 75 percent and 60
percent for seeds from pistillate and perfect flowers, respectively.
Seeds remain viable for more than 1 year and may germinate any time
germination requirements for moisture and light are met.  The seeds are
light dependent; thus few seedlings occur on muddy sediments where seeds
are easily covered.  Sandy, wet, vegetation-free substrates provide the
best germination sites because seeds are not easily covered, and if they
are covered, sufficient light for germination is able to penetrate the
thin sand covering.  In fact black rush seedlings are almost always
restricted to barren, sandy areas.  They are almost never found in
established black rush stands or other marsh types.  Germination
decreases with increasing salinity, and is inhibited by salinities above
15 parts per thousand.  In Mississippi, germination which leads to
successful plant establishment occurs from November to April.  Spring
and summer germinants are less likely to survive because surface
sediments dry during the summer and fall resulting in seedling death.


SITE CHARACTERISTICS : 
Black rush inhabits coastal tidal marshes and may extend as far as 10 to
15 miles inland along river estuaries [6].  It typically occurs in
nearly pure stands, forming a distinct vegetation zone that may be
several hundred yards to several miles wide [25].  This zone usually
encompasses a narrow elevational range.  In Mississippi, the black rush
zone covered an elevational range of only 0.7 feet (0.2 m), from 1.7 to
2.4 feet (0.54-0.75 m) above mean low water [6,25].

Salinity:  Black rush tolerates a wide range of salinities.  It has a
greater tolerance to salt than most plants inhabiting brackish or saline
marshes.  High-salinity soils tend to favor black rush by removing less
salt-tolerant competitors.  Under laboratory conditions, it grows best
in freshwater, but its natural inland distribution is limited by low
salinity.  Along Mississippi coastal rivers, black rush is replaced
inland by sawgrass or tree-covered swamp as salinity decreases.  Growth
in freshwater habitats may be restricted by soil organisms which feed on
black rush rhizomes [6].

Soil:  Black rush grows on a wide variety of soil types, ranging from
almost pure sand to fine silt and clay mixtures.  It grows in highly
organic soils, including peat.  In black rush stands in Mississippi,
soil pH ranged from 4.5 to 7.0 [6].  


SUCCESSIONAL STATUS : 
Obligate Climax Species

Black rush is considered a climax species [4].


SEASONAL DEVELOPMENT : 
In contrast with associated marsh plants which have a single annual
flush of growth, black rush produces new shoots and leaves throughout
the year [7].  Flowering in several states is as follows [3,21]:

southern Florida - March
southeastern Louisiana - March and April
Mississippi - late January to May, peak in March
North Carolina - January to June

Related categories for Species: Juncus roemerianus | Black Rush